Preventable Midair Collisions Since 26 June 1997 Request Denied for
Notice of Proposed Rulemaking (NPRM) 28996
Altimeter-Compass Cruising Altitude Rule (ACCAR)

Collision
Date

Lives
Lost

Approximate
Location
(links to source text)

Colliding Aircraft
(links to discussion of
relevance to ACCAR)

September 13, 1997

33

65 miles west of Namibia

U.S. Air Force C-141 Starlifter 
German Tupelov 154

October 7, 1997

3

Robbins, North Carolina

Aircraft: Beech 35-C33A: N2050W 
Piper PA-32-260: N3940W

February 11, 1998

1

Morgan Hill, California

Aircraft: Beech J35: N8343D 
Boeing CH-47D: ARNG/A>

July 16, 1998

2

Burley, Idaho

Grumman-Schweizer G-164B: N6649K 
Rockwell S-2R: N5036X

October 5, 1998

1

Vermilion 331, GM

Bell 407: N403PH 
Aerospatiale AS-355-F1: N5792H

November 18, 1998

22

Southern Gulf of Mexico

Two Petroleos Mexicanos (Pemex) helicopters

November 07, 1999

0

Longmont, CO

Cessna 150E: N6158T
Cessna TU206F: N8758Q

November 17, 1999

0

Seattle, WA

Bell 206L-3: N206AC
Bell 206B: N5735A

February 15, 2000

0

Parkertown, OH

Piper PA-28-236: N8264G
Cessna 172M: N1742V

May 25, 2000

2

Noble, OK

Cessna 152: N45973
Cessna 182L: N974SR

August 09, 2000

11

Burlington TWP., NJ

Piper PA-31 NAVAJO: N27944
Piper PA-44 SEMINOLE: N2225G

November 16, 2000

1

Bradenton, FL

Lockheed-Martin F-16CG: USAF
Cessna 172N: N73829

November 26, 2000

1

Katy, TX

Cessna 172N: N6521D
Cessna 150E: N3588J

February 6, 2001

2

Platter, OK

Cessna 152: N114SS
Cessna 172P: N96621

February 15, 2001

4

Long Beach, CA

Cessna 152: N68763
Cessna 172N: N4686G

June 02, 2001

2

Anguilla, MS

Air Tractor 502B: N257LA
Cessna 188B: N731KG

June 20, 2001

1

Uxbridge, Canada

Cessna 170B: C-GKGG
Robinson R-22: C-FFFM

July 1, 2002

71

Uberlingen, Baden-Wurttemberg, Germany

Bashkirian Airlines Tupolev Tu-154
DHL European Air Transport Boeing 757

October 27, 2002

2

Coral Springs, FL

Cessna 172M: N9840V
Cessna 172N: N6101F

January 24, 2003

5

Denver, CO

Piper PA-31T: N360LL
Cessna 172P: N52241

June 17, 2003

5

Deerfield Beach, Florida

Cessna 172N: N4903F
Cessna 182Q: N759XA

August 22, 2003

3

Lake Elmo, MN

Cessna 172S: N53033
Piper PA-28-181: N38416

April 09, 2004

0

New Munster, WI

Cessna 172M: N73213
Cessna 182S: N355BD

May 16, 2004

1

Tenino, WA

Cessna 170B, registration: N3510D
Cessna 210J, registration: N3329S

August 07, 2004

2

Kinnelon, NJ

Cessna A150L: N6186F
Piper PA28-140: N95314

August 22, 2004

3

Malibu, CA

Bellanca 7ECA: N53879
Pollard & Huntley Thorp T-18: N7618T

January 18, 2005

1

Hollister, OK

Cessna T-37B: 66-8003
Air Tractor AT-502B: N8526M

July 14, 2005

0

Bonita, LA

Ayres S2R-T34: N61220
Ayres S2R-T15: N3098R

November 05, 2005

1

Pohatcong, NJ

Cessna 172A: N7467T
Joseph E. Crosby Zodiac CH 601HDS: N6384E

February 08, 2006

3

El Cajon, CA

Cessna 172RG: N9531B
Cessna 182Q: N759KE

April 23, 2006

5

Chugiak, AK

Cessna 170B: N4488B
Cessna 172: N5049A

September 29, 2006

154

State of Mato Grosso, Brazil
(120 miles east of Peixoto de Azevedo)

Boeing 737-800 SFP: PR-GTD
Embraer E135 Legacy: N600XL

Total number of lives unnecessarily lost so far since denied request
for ACCAR NPRM 28996 is now equal to 342.

Web site collection of historical documents about ACCAR.

"U.S. Aviation Regulations Increase Probability of Midair Collisions"
by Robert Patlovany, Risk Analysis, Vol. 17, No. 2, April 1997

"Climb and Maintain What?"
by Robert Patlovany, Aviation Safety, December 1998, pages 8-10,
resulting in;
"Cruisin' for Bruisin'" (Unicom, or Letters to the Editor), February 1999, pages 27-28

"Head-On Doesn't Have to Be," Aviation Safety, March 2003, Unicom, pages 27-28.

"A Linear Altitude Rule for Safer and More Efficient Enroute Air Traffic [PDF download]"
by Russ A. Paielli, Air Traffic Control Quarterly, Vol. 8, No. 3, Fall 2000,

Perform your own midair collision counting analysis with Java applet version of 1997 Basica program.

E-mail comments or questions welcome at: rpatlovany((_AT_))rocketmail((_DOT_))com

Source

NTSB Identification: N.A., September 13, 1997
Aircraft: U.S. Air Force C-141 Starlifter
Aircraft: German Tupelov 154
Injuries: 33 Fatal

HISTORY OF FLIGHT

"Air Force faults Germans in crash," The Denver Post, 3/31/98, page 7A.

U.S. Air Force investigators have concluded that a German military plane was flying at the wrong altitude off the coast of Africa on September 13, 1997, when it collided with a U.S. military C-141, killing all 33 people on the planes, defense officials said Monday.

A report holds the crew of the German Tupolev 154 chiefly responsible for the late-afternoon crash at 35,000 feet over the Atlantic about 65 nautical miles west of Namibia. But the report also cites air traffic controllers in Luanda, Angola, and the "convoluted" routing of air traffic control messages through a complicated regional communications system as "substantially contributing" factors.

"U.S., Germany spar over redresses," The Denver Post, 4/25/98, page 3A, by Matthew L. Wald, The New York Times

The surviving relatives of the Germans killed in the cable car accident in Italy were getting close to receiving compensation from the United States, until the issue of the crew killed in an Air Force C-141 Starlifter five months earlier delayed the action.

Twenty people on the cable car, including seven Germans, were killed when a low-flying Marine Corps jet hit the ski gondola's support cable on Feb. 3, 1998. Last month the Senate voted a payment of $40 million, or $2 million per victim.

By a grim happenstance, five months before the gondola accident, on Sept. 13, 1997, an Air Force Starlifter and a Luftwaffe plane collided 35,000 feet over the South Atlantic off Namibia. On March 31, 1998, the German government said in a report that the German crew were at fault, because they were flying their Tupelov 154 eastward at an altitude reserved for westbound traffic.

The crashes were five months and 3,000 miles apart, but they are linked now because in late March, Sen. Charles Robb, D-Va., attached an amendment to a catch-all spending bill to provide $2 million for each victim of the accident in Italy. Two days later, Sen. Strom Thurmond, R-S.C., approached Robb with new language that would bar payment to the German families--but not the families from Belgium, Poland, or Italy--until the German government settled the claims of the American families.

The Senate did not vote on that suggestion, but Robb accepted it, and it is now part of the package that House and Senate Negotiators are considering as they iron out their other differences.

"If the U.S. Senate does not look out for the interests of the American servicemen and women, who will?" Thurmond said.

German ambassador Juergen Chrobog responded: "I do not think it is helpful to link compensation issues. Nor is it customary in light of the close cooperation of our two countries within the NATO alliance."

Back to Top

ACCAR Relevance

The fact is that in USA airspace alone, over 400 human errors are committed every year by either air traffic controllers or pilots. Accounting for errors on an international scale, there are probably tens of thousand of these regularly occurring breakdowns in performance. Every one of these errors reduces or eliminates midair collision safety. In Namibian airspace, where TCAS (a ground-computer-based safety system for independently and automatically warning pilots of danger) simply does not have such ground-based support, one human error can easily guarantee a midair collision between the best, most accurate, and experienced international pilots proudly maintaining their assigned or assumed non random formula cruising altitudes. Given that occasionally unexpected and undesired human errors must be expected, the German crew's error was foreseen in the comprehensive technical analysis of the midair collision process in Risk Analysis. All the wasted lives and expensive hardware could have almost certainly been saved if the international aviation safety community had been notified of the Risk Analysis conclusions and recommendations for fixing the problem. The Risk Analysis articles explain why with even one of the two air crews using ACCAR, over 75% of the probability of the Namibian collision would have been eliminated.

It seems that the German government was too hasty in accepting all of the blame for this tragic and easily avoidable accident. Safety professionals in every industry know that all safety systems, wherever possible, must be designed as if human error is expected. In contrast to this conventional wisdom for most industries, the cruising altitude rules in the aviation industry for over the last 30 years have been specifically designed to maximize the probability of a midair collision after a single human error, such as the one committed by the Tupelov 154 pilot.

Back to Top


Source

NTSB Identification: MIA98FA007A/MIA98FA007B, Tuesday, October 07, 1997 in ROBBINS, NC
Aircraft: Beech 35-C33A, registration: N2050W
Aircraft: Piper PA-32-260, registration: N3940W
Injuries: 3 Fatal

HISTORY OF FLIGHT: The pilot of Beech 35, N2050W, phoned the Leesburg Automated Flight Service Station (AFSS) to file a round trip IFR flight plan, but the briefing specialist inadvertently inputted the departure time as 1130 UTC instead of 1530 UTC (1130 local). The Beech flight departed VFR, and the pilot attempted to obtain an IFR clearance, but the controller advised him that there was no IFR flight plan in the system. The pilot advised the controller that he would proceed VFR. While en route, the Beech was on a north-northwesterly course, when it began to converge with Piper PA-32, N3940W, that was on a east-northeasterly course at about the same altitude. At about that time, the Beech pilot contacted an ATC facility and stated that his flight was level at 5,500 feet. He was given a discrete transponder code to squawk, and the pilot complied. The controller immediately advised the pilot that traffic was off to his left, but there was no acknowledgement. Both airplanes crashed into a rural area. An investigation revealed the nose landing gear of the Piper collided with the left wing tip of the Beech. Review of the FAR's revealed that while flying VFR between 180 and 359 degrees magnetic course, above 3,000 feet above ground level (agl), the pilot should fly at even thousand feet altitudes plus 500 feet. VFR flight between 0 and 179 degrees, above 3,000 feet agl, should be at odd thousands plus 500 feet. The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
failure of the pilots in both aircraft to see-and-avoid each other's airplane (inadequate visual lookout), and failure of the Beech pilot to operate his airplane at a correct Visual Flight Rules (VFR) cruising altitude for his route of flight.

Back to Top


Narrative by NTSB (autopsy results deleted)

HISTORY OF FLIGHT

On October 7, 1997, about 1337 eastern daylight time, a Beech 35-C33A, N2050W, and a Piper PA-32-260, N3940W, both registered to separate private individuals, collided in flight near Robbins, North Carolina. Visual meteorological conditions prevailed at the time and an IFR flight plan was filed for the 14 CFR 91 personal flight for the Beech airplane. No flight plan was filed for the business flight of the Piper airplane, also operating in accordance with 14 CFR 91. Both airplanes were destroyed and the private-rated pilot, the sole occupant of the Beech airplane was fatally injured. The private-rated pilot and one passenger in the Piper airplane were also fatally injured. A power line was damaged. The Beech flight originated about 1300, from the Marion County Airport, near Marion, South Carolina. The Piper flight originated about 1315, from the Wilgrove Air Park, Charlotte, North Carolina.

According to a voice tape from the Greensboro, North Carolina, Approach Control facility, the pilot of the Beech airplane contacted the facility and stated that his flight was located 10 miles north of the Sandhills VOR on the 355-degree radial level 5,500 feet, VFR to the Blue Ridge Airport, Martinsville, Virginia. The pilot was advised to squawk 0101 on his transponder, which the pilot acknowledged. The controller stated that the flight was radar identified and traffic was close off his left side at 5,500 feet. There was no further contact from the pilot of the Beech airplane. There was no ATC contact with the pilot of the Piper airplane.

Witnesses near the accident site reported hearing a loud sound, then observed parts falling. None of the witnesses reported seeing the airplanes before the collision. Wreckage from both airplanes was scattered over a 1/3 mile rural populated area.

 Review of recorded radar data pertaining to the flight of the Beech airplane revealed that at 1336.09, the first discrete transponder code 0101 was indicated and the reported altitude was 5,300 feet. There were six other radar hits and the reported altitude for all was 5,300 feet. The last radar target was located at N35 degrees 28 minutes.32 and W 079 degrees 37 minutes.34. Discrete radar data was not obtained for the Piper airplane which was emitting a code signal of 1200. A radar target displaying the 1200 code at 1337.10, was located at N35 degrees 28 minutes.32 and W079 degrees 37 minutes.43. The altitude reported was 5,400 feet.

COMMUNICATIONS

Review of communications with the pilot of the Beech airplane and the Leesburg Automated Flight Service Station (AFSS) located in Leesburg, Virginia, revealed that between 0612-0618 local time (1012-1018 UTC), the pilot received a weather briefing and filed two IFR flight plans. The first for a flight from the Blue Ridge Airport in Martinsville, Virginia, to the Marion County Airport in Marion, South Carolina. The proposed time of departure was 0800 local (1200 UTC). The second flight was for the return flight with a proposed departure time of 1130 local (1530 UTC). The planned altitude of the return flight was 6,000 feet and the route of flight was to the Sandhills VORTAC then to the destination airport. The proposed time of departure indicated in the FAA system pertaining to the flight plan for the return flight was 1130 UTC (0730 local). Review of recorded communications with the Florence, South Carolina, approach control facility pertaining to the Beech airplane revealed that after departure, the pilot contacted the facility and advised the controller that an IFR flight plan had been filed to his destination airport. The controller advised the pilot that there was no flight plan stored for the flight and asked the pilot his flight plan route. The pilot advised the controller "ok sir ah don't bother with * it's such a nice day i'll go vfr i won't worry about it i appreciate your help." The controller acknowledged this.

ADDITIONAL DATA/INFORMATION

Review of the flight planning for the route of flight of the Beech airplane as proposed in the IFR flight plan revealed that the magnetic heading from the Sandhills VORTAC to the destination airport was about 355 degrees magnetic. Additionally, the destination airport was located about 35.1 nautical miles and 004 degrees magnetic from the Greensboro VORTAC. Located in the wreckage of the Beech airplane was an RNAV computer which indicated about 359 in the bearing window and about 36 in the distance window and was selected to the en route position. According to the manufacturer, in part in the en route mode, the user selects waypoints that are offset from a VORTAC. The DME indicator indicates the distance from the selected waypoint.

Review of the Federal Aviation Regulations pertaining to VFR altitudes to be flown in cruise flight when operating below 18,000 feet mean sea level and flying above 3,000 feet agl revealed that when flying on a magnetic course of 180 degrees through 359 degrees, the altitude to be flown is any even thousand foot altitude plus 500 feet (such as 4,500, 6,500, or 8,500).

Back to Top

ACCAR Relevance

The Altimeter-Compass Cruising Altitude Rule (ACCAR) would have given these aircraft about 200 ft of vertical separation, whether the Beech had picked a heading of either 355 or 004. With the hemispherical cruising altitude rule of Federal Aviation Regulation (FAR) 91.159 , the Beech pilot was flipping a coin (in his choice of navigation transmitter radials to follow to his destination) between needing to be on a coinciding altitude option for a heading of 004, or on a "safe" altitude option for a heading of 355. Philosophically speaking, a cruising altitude rule that makes 1000 ft of legal difference for 9 degrees in course difference is not very mathematically consistent with the hard physics of the midair collision process described in the Risk Analysis article. Obviously, the Air Traffic Control (ATC) warning of proximity to another aircraft was inadequate (as allowed by FARs) for preventing the collision. Controllers are almost never required to issue warnings to enroute Visual Flight Rules (VFR) aircraft in Visual Meteorological Conditions (VMC). To their credit, many controllers issue many advisory warnings to VFR pilots when time is available. Individual controllers really do care. However, the ATC system accepts absolutely no responsibility for enroute VMC collisions if even one of the pilots was following a VFR flight plan. Instrument Flight Plan (IFR) pilots on IFR flight plans are 100% responsible for avoiding collisions with VFR traffic in VMC. The full responsibility for a midair collision goes to ATC only when both aircraft are piloted in Instrument Meteorological Conditions (IMC) exactly per ATC instructions and FARs.

In any case, it looks like both aircraft were cruising VFR, and all three victims probably would have survived if the pilots had been using ACCAR as accurately as they were apparently using the 91.159 easterly altitude.

The Risk Analysis article destroying the presumed (but unsupported) safety basis of the hemispherical cruising altitude rules was in the April 1997 issue, which reached members of the Society for Risk Analysis very late in June 1997. The petition for NPRM 28996 was dated and mailed on June 26, 1997. The letter from the Federal Aviation Administration (FAA) denying NPRM 28996 a fair review was dated September 19, 1997. The Robbins midair collision occurred October 7, 1997. One FAR says that the FAA Administrator has the authority to change an FAR in an emergency without the delay of a formal NPRM review and comment period. In the nuclear power and nuclear weapons industries (unlike the aviation industry), the discovery of a technical error in any document establishing a safety basis for routine operations always requires an immediate response with some kind of documented corrective action. This response is in the form of either: (1) a formal, documented justification for continued operations (specifying temporary compensatory actions and a long-term corrective action plan), or (2) an immediate shutdown of all operations compromised by the technical error pending reestablishment of the safety margins compromised by the technical error. The aviation regulating FAA apparently differs from the nuclear regulating NRC and DOE in this respect. The FAA Administrator had at most about three months following the petition to prevent this collision. Considering the timing, only an Administrator's emergency revision of FARs 91.159 and 91.179 would have been prompt enough to avoid the Robbins collision. The Robbins collision certainly qualifies as one that could have been easily avoided given the information that was available over 30 years ago in the Air Facts (950 kb download, Adobe PDF format) article from February 1968. This article advocated ACCAR in the fourth of a series of non technical, common sense articles bemoaning the logical inconsistencies in the hemispherical cruising altitude rules ("Automatic Altitude & Heading Separation", by Leighton H. Collins [father of Richard Collins, Editor-at-Large for Flying]).

Back to Top


Source

NTSB LAX98FA086A, LAX98FA086B, Wednesday, February 11, 1998 in MORGAN HILL, CA
Aircraft: Beech J35, registration: N8343D
Aircraft: Boeing CH-47D, registration: ARNG
Injuries: 1 Fatal, 4 Uninjured.

HISTORY OF FLIGHT

On February 11, 1998, at 1525 hours Pacific standard time, a Beech J35, N8343D, collided with a California Army National Guard Boeing CH-47D, S/N 91-0234, the lead ship of a two helicopter formation flight near Morgan Hill, California. The lead and trail aircraft were using the call signs Schooner 14 and Schooner 44 respectively. The Beech was destroyed and the pilot, the sole occupant, received fatal injuries. The Boeing sustained substantial damage; however, neither the pilot, copilot, nor the two flight engineers onboard were injured. The Beech was being operated as a personal flight by its owner/pilot, while the Boeing was being operated as a military flight by the California Army National Guard when the accident occurred. The Beech originated at 1510 from the Reid-Hillview of Santa Clara County airport in San Jose, California. The Boeing originated from the Monterey Peninsula airport, in Monterey, California, at 1505. Visual meteorological conditions prevailed at the time. The Boeing aircraft had a VFR flight plan on file, the Beech had none on file. The helicopter formation was on a northerly heading at 2,500 feet msl when the westbound Beech J35 collided with the lead ship. On impact with the right rear section of the Boeing fuselage, the right wing of the Beech separated and the aircraft made an uncontrolled descent. The pilot of the Boeing made a precautionary, run-on landing and then performed an emergency shutdown. The pilot of the Boeing was flight following with San Francisco Bay TRACON at the time, but had not received any VFR traffic advisories before the collision occurred. The pilot of the Beech was not currently communicating with any FAA air traffic control (ATC) facility. The crew in the Boeing all stated that they did not see the Beech at any time before the collision. Some of the crewmembers on the second Boeing in the formation reported first seeing the Beech approach their formation from the right about 3 to 5 seconds before the collision occurred. They stated that neither aircraft made in any changes in heading or altitude before the collision. Visual meteorological conditions prevailed with a 20-mile visibility and scattered clouds at 3,000 feet.

Back to Top

ACCAR Relevance

On February 11, 1998, the first helicopter of a two helicopter military formation flight headed northbound collided with a westbound civilian aircraft at 2500 ft msl near Morgan Hill, California (see attached NTSB summary report above). The four surviving members of the leading military crew reported that they never say the civilian aircraft prior to the moment of impact, while the crew of the uninvolved trailing helicopter reported detecting the collision threat only 3 to 5 seconds prior to impact. This is exactly the kind of collision scenario that the Risk Analysis paper modeled as having an unnecessarily high probability under current regulations. Recall that aircraft below 3000 agl are not required to obey the hemispherical formula altitudes. Many pilots falsely assume that the hemispherical cruising altitude rules legally required only above 3000 ft agl must also be safer below 3000 ft agl than the random altitudes legally allowed only down low, based on the absolutely true assumption that collision probabilities are not in any way influenced by altitude above ground. The false part of the assumption is understandably common to any pilot who has not read the mathematically rigorous Risk Analysis explanation that at all altitudes, random cruising altitudes are at least four times safer than strict compliance with the cruising altitude rules. If the FAA had advised pilots of the ACCAR recommendations and admitted to its erroneous regulatory history in a timely manner, the Morgan Hill aircraft would have had about 250 ft of vertical clearance when their paths crossed.

One of three anonymous expert peer reviewers for the Risk Analysis article admitted to using the technically flawed hemispherical cruising altitude rules below 3000 ft agl, where such conformance is not required (and not wise). The reviewer was understandably acting on his blind faith acceptance of FAA infallibility in formulating safety regulations. If a similar blind faith was adopted by the westbound civilian at 2500 ft msl (even 1000s + 500 for westbound pilots), while the northbound formation flight was most likely ever so slightly westbound with unquestioning faith in the hemispherical formula, then an easily avoidable disaster would have been encouraged. The less that 5 seconds of visible threat warning reported only by the trailing crew is exactly the kind of scenario predicted by Equation 5 of the Risk Analysis article as a most likely outcome for encounters between aircraft with even the most vigilant and conscientious professional pilots. The Equation 5 discussion explains exactly why it is impossible for pilots to guarantee their own safety using FAA regulations and midair collision safety recommendations. Equation 5, considered with Figures 1 and 2 of the article, explains why ACCAR is a far better alternative than what the FAA orders pilots to use at higher altitudes. In summary, a 5-second visible closing time experienced by a pilot with a 20-second scan cycle results in a 25% probability of detecting a collision threat before impact.

Back to Top


Source

NTSB Identification: SEA98LA138A, SEA98LA138B, Thursday, July 16, 1998 in BURLEY, ID
Aircraft: Rockwell S-2R, registration: N5036X
Aircraft: Grumman-Schweizer G-164B, registration: N6649K
Injuries: 2 Fatal

HISTORY OF FLIGHT: On July 16, 1998, approximately 0800 mountain daylight time, a Rockwell S-2R agricultural aircraft, N5036X, registered to Kinney Aviation Inc. (d/b/a Farm Dusters) of Missoula, Montana, and a Grumman-Schweizer G-164B agricultural aircraft, N6649K, registered to Farm Flite Inc. of Burley, Idaho, collided in flight approximately 12 miles northwest of Burley, Idaho. Both aircraft subsequently impacted terrain. Both aircraft were substantially damaged, and the commercial pilot-in-command of each aircraft was fatally injured. Preliminary information indicated that at the time of the collision, both aircraft were operating under 14 CFR 91, with N6649K loaded and heading to a job site and N5036X empty and returning from a job site. Visual meteorological conditions (clear skies and 30 miles visibility) were reported at Burley at 0748, and neither aircraft had filed a flight plan. Evidence developed during on-scene investigation indicated that at the time of the collision, the S-2R was heading generally northeast and the G-164B was heading generally southeast. U.S. Naval Observatory astronomical data indicated that at Burley at 0800 on July 16, the azimuth of the sun was 076.9 degrees true, at an altitude of 17.6 degrees.

Back to Top

ACCAR Relevance

On July 16, 1998, near Burley, Idaho, two crop duster pilots died when their aircraft collided in an accident that could easily have been prevented if both pilots had known and followed NPRM recommendations for using ACCAR to minimize midair collision risk at all altitudes. At first, it may seem impossible that the FAA could have prevented what was probably a low altitude collision by fixing regulations that are only applicable to higher altitude operations. After all, the two crop duster pilots were almost certainly not required to use the technically flawed hemispherical cruising altitude regulations at their most likely collision altitude. Crop dusters observed cruising between runway and chemical application site very seldom fly higher than 3000 ft agl where the defective cruising altitude rules actually do apply. However, if the doomed pilots had known about and used ACCAR as a result of a reasonable FAA response to the request for an NPRM, then these two pilots would have harmlessly crossed paths with about 250 ft of vertical separation. Based on observations of many rural crop duster flights, the doomed crop dusters were most likely flying less than a few hundred feet over the highest obstructions when they collided. It is most important to recognize that if very many fly very close to the ground (or very close to any non-random common altitude), a lot of available level cruising airspace volume is being wasted for systematically avoiding midair collisions.

Back to Top


Source

NTSB Identification: FTW99FA001A, FTW99FA001B, Monday, October 05, 1998 in VERMILION 331
Aircraft: Bell 407, registration: N403PH
Aircraft: Aerospatiale AS-355-F1, registration: N5792H
Injuries: 1 Fatal, 1 Minor

HISTORY OF FLIGHT: On October 5, 1998, approximately 0908 central daylight time, a Bell 407 helicopter, N403PH, registered to National Leasing Corporation, Louisville, Kentucky and operated by Petroleum Helicopters Incorporated (PHI), Lafayette, Louisiana, collided in flight with N5792H, an Aerospatiale AS-355-F1 helicopter, registered to and operated by Tex-Air Helicopters Incorporated, Houston, Texas. Both aircraft were operating over open ocean water in the Gulf of Mexico, approximately 115 miles south of the White Lake VORTAC. The pilot of N403PH executed a forced auto-rotation landing into the water. The disposition of N5792H after the collision is unknown. N403PH was destroyed (collision, water landing, and recovery damage inclusive) and N5792H was not recovered. The commercial pilot of N403PH sustained minor injuries, and the commercial pilot ofN5792H was fatally injured. There were no passengers onboard either helicopter. Visual meteorological conditions prevailed and respective company flight plans were filed for each of the Title 14 CFR Part 91 positioning flights. N403PH departed from oil platform, Vermilion 331, and was en route westbound to another platform, East Cameron 321A. N5792H departed Cameron, Louisiana, and was enroute southeast bound to oil platform, Vermilion 370. According to the surviving pilot of N403PH, he was flying at 1,000 feet AGL, on a westerly bearing, when he "heard" another aircraft. He then saw a helicopter [N5792H] between his "three-thirty and four o'clock" position, seemingly to be in a "hard right turn." He then initiated a "hard" left turn away from the other helicopter. Immediately afterwards, he noticed that the lower right portion of his helicopter's nose section was missing along with both of the tail rotor control pedals. He entered an autorotation, and landed in the water with the skid mounted float system deployed. The helicopter stayed upright for about "thirty" seconds, and as it rolled over, the pilot exited through the pilot side cabin door. Rescuers arrived via helicopters and a boat. The helicopter was retrieved and the pilot was rescued from the water. One of the rescue helicopter pilots reported that he thought he saw N5792H in the water briefly before it sank. He also stated that he spotted an "empty" life raft in the vicinity. During rescue operations, the fatally injured pilot of N5792H was found floating in the water. The only portions of N5792H that were found were two small sections of the landing gear (skid) assembly, both floats (deflated), and three pieces of under belly fuselage skin. N403PH (Bell 407) and the aforementioned portions of N5792H (Aerospatiale AS-355-F1) were recovered and transported to a PHI facility in Lafayette, Louisiana, for examination by the NTSB. The lower right section of the nose assembly and tail rotor pedals of N403PH were missing and adjacent fuselage skin was found crushed and deformed. Mostly all of the helicopter was intact (excluding collision and recovery damage) with the exception of the aft portion of the tail boom and tail rotor assembly, which was not recovered.

Back to Top

ACCAR Relevance

On October 5, 1998, two helicopters collided at 1000 ft agl/msl over the open ocean of the Gulf of Mexico off the Louisiana coast, most likely while in level cruising flight. A very natural and common human tendency for operators of all kinds of equipment from aircraft to automobiles is to make the measurement feedback needle point to a cardinal value. Left to themselves, pilots, being human, tend to pick cruising altitudes like 1000 ft, 2000 ft, 3000 ft, etc., the same as automobile drivers tended to stabilize on 50 mph, 60 mph, 70 mph, etc., throughout most of automotive history. After the hated 55-mph national speed limit was enacted, manufacturers converted to speedometer scales with numbered increments of 35 mph, 45 mph, 55 mph, etc., in the hope of improving compliance with energy conservation regulations through human factors engineering. The Risk Analysis article explains exactly why this nature human tendency increases midair collision risk through the common mode failure selection of similar non-random altitudes.

Back to Top


Source

NTSB Identification: N.A., November 18, 1998 in Southern Gulf of Mexico
Aircraft: Two Petroleos Mexicanos (Pemex) helicopters
Injuries: 22 Fatal

HISTORY OF FLIGHT:

Associated Press, The Denver Post, 11/19/1998, for Collision 11/18/98

Two helicopters crashed Wednesday morning over the southern Gulf of Mexico, killing at least 18 people, the government oil monopoly Petroleos Mexicanos reported. The accident occurred as the private helicopters were flying between two oil platforms, Pemex said in a news release. The helicopters carried a total of 22 people. Eighteen bodies have been recovered and workers were searching for the other four victims.

Back to Top

ACCAR Relevance

The November 18, 1998, midair collision with 22 fatalities under Mexican jurisdiction might have been avoided if our FAA had properly responded to midair collision safety recommendations in a timely manner back in July 1997, and then communicated the proposed improvements to FAA counterparts in other nations. The newspaper account implies that the doomed helicopters may have been cruising in level flight between offshore oil platforms at the time of their collision. The Mexican collision appears to be exactly the same accident scenario as the single fatality collision off the Louisiana coast, i.e., level cruising flight at common cardinal altitudes. Unfortunately, with no survivors and no flight data recorders, a guess about a common mode relationship between the Mexican and Louisianan offshore collisions is only speculation. Observations of coastal helicopter operations supporting offshore oil platforms along the Texas and Louisiana shorelines reveal that, as with crop duster pilots, helicopter pilots generally cruise at minimal legal altitudes where the fraction of the available maneuvering volume actually used is just as non-randomly and unnecessarily limited as with the unnecessarily thin slabs of legal cruising volume defined by the FARs at altitudes above 3000 ft. Granted, the FAA has no jurisdiction in regulating the safety of Mexican flight operations. However, much of the foreign aviation world follows the leadership of the FAA in aviation safety technology and regulations. There was plenty of time from the initial request for NPRM 28996 until the Mexican collision to have make the necessary changes to save 22 lives.

Back to Top


Source

NTSB Identification: DEN00LA016A, DEN00LA016B; Accident occurred Sunday, November 07, 1999 in LONGMONT, CO
Aircraft: Cessna 150E, N6158T
Aircraft: Cessna TU206F, N8758Q
Injuries: 3 Uninjured

HISTORY OF FLIGHT: N6158T and N8758Q were both maneuvering 3 miles southwest of the airport at 6,100 feet msl while waiting for a break in traffic at the airport. The pilot of N6158T observed N8758Q to his right with their flight paths converging. He banked to the left, and the two aircraft then made contact. Both aircraft landed at the airport without further incident. N8758Q sustained minor wingtip damage; however, a rib in the left wingtip of N6158T was bent. According to FAR Part 91.113 (b), 'When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft.' Subpart (d) states, 'When aircraft of the same category are converging at approximately the same altitude (except head-on, or nearly so), the aircraft to the other's right has the right-of-way.'

The National Transportation Safety Board determines the probable cause(s) of this accident as follows: The pilot of N6158T's failure to follow right-of-way VFR procedures for converging aircraft and the pilot's inadequate visual lookout.

Full narrative exerpts

DEN00LA016A

On November 7, 1999, approximately 1130 mountain standard time, a Cessna 150E, N6158T, and a Cessna TU206F, N8758Q, both owned and operated by the pilots, collided in midair 3 miles southwest of Vance Brand Airport, Longmont, Colorado, while both were maneuvering. N6158T sustained substantial damage, and N8758Q received minor damage. There were no injuries to the private pilot and one passenger aboard N6158T, or to the commercial pilot and sole occupant aboard N8758Q. Visual meteorological conditions prevailed, and no flight plans were filed for either local flight being conducted under Title 14 CFR Part 91. The flights of N6158T and N8758Q originated at 1030 and 1000, respectively.

According to the pilot of N6158T, he departed the airport for a local flight, and the sky was clear with visibility greater than 20 miles. Recorded weather observations at Broomfield, the closest weather reporting facility located 15 miles to the south, confirmed that the visibility was 60 miles with clear skies. An hour later, the pilot returned to an area southwest of the airport. He circled in the area to lose altitude and "wait for a gap" in traffic to enter a left downwind for runway 29. He stated that the traffic was "fairly heavy" and the airport's CTAF (common traffic advisory frequency) was busy with traffic reports and parachute jumping activity.

He made a position report over the CTAF and stated his intention to enter the downwind for runway 29 at the midfield position. While approximately 3 miles from the airport at 6,100 feet above mean sea level (msl), he observed N8758Q to the right, "slightly above us and a little behind us, very close and closing, our flight paths converging at approximately 30 degrees." The pilot stated that he banked hard to the left, and immediately felt a "thud" as the two aircraft made contact. He then observed N8758Q to the right and slightly lower in altitude, flying to the right with no visible damage. He completed a 360 degree turn to the left, and verified that he was still able to maintain control of the aircraft and that the landing gear was still attached. He then flew a normal traffic pattern, and landed at the airport without further incident.

According to the pilot of N8758Q, the traffic pattern was congested and he was aware that skydiving activity was in progress. He proceeded west of the airport and then south. He made three 360 degree turns, then headed toward the airport heading 020 degrees. He stated that while approximately 3 to 4 miles from the airport, he "felt an impact." He continued toward the airport, and landed on runway 29 without further incident. Postaccident examination of both aircraft revealed that N8758Q sustained only minor wingtip damage; however, a rib in the left wingtip of N6158T was bent.

According to Title 14 CFR Part 91.113 (Right-of-way rules: Except water operations) of the Federal Aviation Regulations (FARs), subpart (b) states, "When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft." In addition, according to subpart (d), "When aircraft of the same category are converging at approximately the same altitude (except head-on, or nearly so), the aircraft to the other's right has the right-of-way."

In the pilot of N6158T's Pilot/Operator Aircraft Accident Report (Form 6120.1/2), he was asked what recommendation he could offer as to how the accident could have been prevented. His response was, "Watch for other traffic as if they are not looking or reporting their position, especially near busy uncontrolled airports." He further stated, "Spotting the other [air]craft further away would be a much better way to avoid the situation."

Back to Top

ACCAR Relevance



The midair collision occurred at 6100 feet, which is approximately pattern altitude for Longmont. It is good to be at pattern altitude on the downwind leg where everybody else is expected to be flying left hand rectangles around the pattern. However, the accident pilots were loitering at a common pattern altitude several miles outside of the pattern waiting for a break in the traffic density until they could enter the standard traffic pattern. If everybody outside of the pattern flying in random loitering maneuvers is at pattern altitude in random paths, there is an unnecessarily and artificially high aircraft collision target concentration encouraging midair collisions. Approaching the pattern from a somewhat higher altitude using the ACCAR formula until the last possible minute reduces collision target density until a standard pattern altitude and flight path is needed for a stabilized approach in a safely predictable approach path.

Notice that one pilot "banked hard to the left" immediately before impact. Hard banks immediately increase the collision cross sectional area vulnerable to damage. The NTSB report notes that "N8758Q sustained only minor wingtip damage; however, a rib in the left wingtip of N6158T was bent." If the banking pilot had left wings level and instead used elevator control to dive or climb, the reduced vulnerable collision area would probably have been enough to eliminate the wingtip damage inflicted on both aircraft. Ideally, pilots should leave wings pointed at the incoming threat so that the least amount of their own flying structure is exposed to the expected approach path being penetrated by the collision threat.

Back to Top


Source

NTSB Identification: SEA00FA021A, SEA00FA021B; Wednesday, November 17, 1999 in SEATTLE, WA
Aircraft: Aircraft: Bell 206L-3: N206AC
Aircraft: Bell 206B: N5735A
Injuries: 1 Minor, 2 Uninjured

HISTORY OF FLIGHT: The pilot of N5735A reported that he was transitioning the area of Lake Union (on a local electronic news gathering flight) in a south-southwesterly direction when the two aircraft collided. He stated that he simultaneously saw the other aircraft and felt the impact. After the collision, the pilot initiated a descent and landed on a nearby helipad. The pilot reported that prior to the collision he was monitoring the common traffic advisory frequency (CTAF) for Lake Union (122.90). He stated that just before transitioning the area he reported his position, altitude and heading on 122.90. The pilot of N206AC reported that he departed Boeing Field and was proceeding northbound. He stated that he had just cleared Boeing's Delta airspace and switched to Seattle Radio (122.50) when he '...experienced a loud bang and vibration in the main rotor system'. The pilot initiated a descent to a nearby helipad, and was able to land without further incident. The pilot stated he did not see the other aircraft before, or after the collision. There were no reported mechanical failures or malfunctions that may of contributed to the accident. A calculated convergence angle between the two aircraft indicated that there were no visual restrictions that would have prevented the pilot from seeing the other aircraft.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows: Adequate separation and lookout not maintained by the pilots of both aircraft.

full narrative excerpts

SEA00FA021A

On November 17, 1999 about 1210 Pacific standard time, a Bell 206L-3, N206AC, registered to and operated by Aero-Copters, Inc., as a 14CFR91 commercial flight, and a Bell 206B, N5735A, registered to WPXI, Inc. and operated by KIRO Television as a 14CFR91 commercial flight, collided in mid-air about seven miles north of Boeing Field Airport, Seattle, Washington. Visual meteorological conditions prevailed and no flight plan was filed for N5735A; however, there was a flight plan on file for N206AC. Both aircraft received substantial damage. The commercial pilot of N5735A sustained minor injuries, and his passenger was uninjured. The commercial pilot, the sole occupant of N206AC, was not injured. N206AC departed Boeing Field approximately five minutes prior to the accident with a planned destination of Vancouver, British Columbia, Canada. N5735A departed Boeing Field approximately 36 minutes prior to the accident for a local electronic news gathering flight.

In a written statement, the pilot of N5735A reported that he was transitioning the area of Lake Union in a south-southwesterly direction when the two aircraft collided. He stated that "...I simultaneously saw the other aircraft and felt the impact". The passenger of N5735A, a news photographer, stated that he "...heard a loud bang and felt the helicopter shake". After the collision the pilot determined the aircraft was still controllable and initiated a descent to a rooftop helipad located approximately a 1/2 mile from where the helicopters collided. The pilot landed the aircraft on the helipad without further incident.

After landing at the helipad, the pilot and photographer determined that the other aircraft involved in the collision was operated by Aero-Copters. They contacted Aero-Copters and learned that the other helicopter involved in the collision landed at a nearby helipad.

The pilot of N5735A reported that prior to the collision he was monitoring the common traffic advisory frequency (CTAF) for Lake Union (122.90). He also stated that just before transitioning the area he reported his position, altitude and heading on 122.90.

During a telephone interview and subsequent written statement, the pilot of N206AC reported that he departed Boeing Field, Seattle, Washington, and was proceeding northbound. He stated that he had just cleared Boeing's Delta airspace and switched to Seattle Radio (122.50) when he "...experienced a loud bang and vibration in the main rotor system". The pilot initiated a descent to a nearby helipad at the University of Washington and was able to land without further incident. The pilot reported that after landing he discovered damage to the main rotor blades and suspected that he had collided with a weather balloon.

Neither pilot reported experiencing any mechanical failures or malfunctions prior to the collision.

ADDITIONAL DATA

Preliminary radar data provided by Seattle-Tacoma Air Traffic Control Tower, Seattle, Washington, indicated that N5735A was tracking a heading of 227 degrees magnetic, with an airspeed of 70 knots and an altitude of 1,000 feet above mean sea level prior to the collision; N206AC was tracking a heading of 342 degrees magnetic with an airspeed of 118 knots and an altitude of 1,000 feet above mean sea level.

Back to Top

ACCAR Relevance

Notice that both aircraft were flying at 1000 ft MSL. Unfortunately this is a heuristically common practice in coastal areas that unintentionally concentrates aircraft collision targets in an artificially systematic way. If N5735A headed 227 degrees had been at an ACCAR altitude of 631 or 1631 feet, while the 342 degrees headed N206AC would have been at an ACCAR altitude of 950 feet, this midair collision would have been systematically prevented.

Back to Top


Source

NTSB Identification: NYC00LA081A, NYC00LA081B; Tuesday, February 15, 2000 in Parkertown, OH
Aircraft: Piper PA-28-236: N8264G
Aircraft: Cessna 172M: N1742V
Injuries: 3 Uninjured

HISTORY OF FLIGHT: A low wing Piper was in level flight at 3,700 feet, heading in a northerly direction. A high wing Cessna was climbing through 3,300 feet for a final cruise altitude of 3,500 feet. The pilot of the Piper felt a bump and the windshield broke. Assuming that he had hit a bird, the pilot returned to LPR and landed uneventfully. The pilot of the Cessna noticed a vertical fin just slightly to the right of the airplane. The Cessna impacted the Piper, and both airplanes landed uneventfully at different airports. Examination of the Piper revealed a black rubber streak that on the top of the fuselage, about 5 degrees right of centerline, and extended reward about 4 feet. The vertical stabilizer and rudder were damaged from the top rudder hinge upward. Examination of the Cessna revealed a gash in the fuselage that extended from aft of the firewall to where the wing strut met the fuselage. Pieces of metal and wires were found embedded in the gash. The right hand door was missing from the airplane. A gash and white paint transfer was observed on the nose wheel tire. Inside the cabin area of the airplane was the rudder counter weight from the Piper. The National Transportation Safety Board determines the probable cause(s) of this accident as follows: The inadequate visual lookout by the pilots of both airplanes. full narrative excerpts NYC00LA081A On February 15, 2000, about 1430 Eastern Standard Time, a Piper PA-28-236, N8264G, was substantially damaged during a midair collision with a Cessna 172M, N1742V, near Parkertown, Ohio. The 172M sustained minor damage. The certificated commercial pilot of the Piper, and the certificated commercial pilot and passenger of the Cessna were not injured. Visual meteorological conditions prevailed and no flight plans were filed for the personal flights conducted under 14 CFR Part 91. According to the pilot of the Piper, he departed the Loraine County Regional Airport (LPR), Lorain, Ohio, for a local flight. The pilot stated that while level at 3,700 feet, and heading in a northerly direction, he was "scanning" from right to left, when he felt a bump and the windshield broke. Assuming that he had hit a bird, the pilot returned to LPR and landed uneventfully. The pilot did not recall seeing the Cessna before or after the accident. According to the pilot of the Cessna, he departed from the Griffing Sandusky Airport, Sandusky, Ohio, about 1415. As the airplane was climbing through 3,300 feet for a final cruise altitude of 3,500 feet, (headed SSE) about 2 miles north of Norwalk City, Ohio, the pilot noticed a vertical fin just slightly to the right of his airplane. The pilot stated that "there was no time to take action, there was a slight uplifting and bang!" After impacting the airplane, the Cessna rolled to the left about 45-60 degrees and the pilot felt that he might not recover. The pilot rolled the wings level and looked out the left side of his airplane to see where the other airplane had gone, but saw nothing and assumed that the airplane had crashed. With the passenger door torn off of the airplane, the pilot was concerned with landing quickly, and began to fly towards the Norwalk-Huron Airport (5A1), Norwalk, Ohio. En route to 5A1, the pilot began assessing the damage to his airplane by checking the tail, working the controls, and to see if he had wheels. After determining that the airplane "felt good," the pilot elected not to land at 5A1 and continued flying to his home base, Galion Airport (GQQ), Galion, Ohio. Arriving at GQQ, the pilot flew over the airport several times for ground personnel to determine if the airplane's wheels were still intact, then landed uneventfully.

Back to Top

ACCAR Relevance



Under an ACCAR modification of this scenario, the northerly aircraft at 3700 ft would have been at 4000 ft. The SSE headed aircraft planning to cruise and FAR 91.159 altitude of 3500 ft would have leveled off at about 3400 ft. Evidently, the SSE headed aircraft overshot its intended 3500 ft cruising altitude to hit the northerly aircraft actually at 3700 ft. In any case, these aircraft were on a virtually head-on closing configuration, with the least possible visible time to impact. The pilots say they never saw the other aircraft, not before or after the collision; as is expected for any situation where visible time to impact is less than the time duration of the scan cycle. A northerly pilot trying to fly 91.159 altitudes is almost equally likely to be at odd or even thousand-ft plus 500-ft altitude intervals. The northerly flying pilot for this accident was apparently trying imprecisely to fly an altitude as if his cruise heading was at least slightly east.

In contrast, under ACCAR, there would be no ambiguity for northerly pilots flight either slightly east or west of magnetic north. The northerly headed pilot would have been at about 4000 ft, and the other pilot would have been leveling off at about 3400 ft. This would have provided about 600 ft of vertical clearance, in contrast to 91.159 aircraft, which if both easterly, would have been required by law to be at exactly the same altitude in the most dangerous as possible head-on geometry.

Back to Top


Source

NTSB Identification: FTW00FA154A, FTW00FA154B; Thursday, May 25, 2000 in Noble, OK
Aircraft: Cessna 152: N45973
Aircraft: Cessna 182L: N974SR
Injuries: 2 Fatal

HISTORY OF FLIGHT: The Cessna 152 departed the airport to the southeast for the local training area to practice commercial flight maneuvers. The Cessna 182 departed the same airport approximately 9 minutes after the Cessna 152 on a cross-country flight. Radar data depicted the Cessna 182 at an altitude of 2,000 feet agl heading to the southeast. Altitude data was not available from the Cessna 152, however, radar track data depicted a figure-eight pattern. At the time of the last radar returns, the targets were about 12 nm southeast of the departure airport, and the Cessna 152 was approximately 1/4 nm southeast of the Cessna 182. The Cessna 152 was heading to the west, and the Cessna 182 was heading to the southeast. The Cessna 152 spinner tip was found imbedded in the left main landing gear attachment point of the Cessna 182. The Cessna 182 left wing strut was severed 9 inches from the fuselage attachment point. The sever was perpendicular to the length of the strut. The Cessna 182's left wing was found between the Cessna 152 and Cessna 182 wreckage. The Cessna 182's left main landing gear and the Cessna 152's propeller were not located. The National Transportation Safety Board determines the probable cause(s) of this accident as follows: the failure of both pilots to maintain visual lookout.

full narrative excerpts

FTW00FA154A

HISTORY OF FLIGHT:

On May 25, 2000, at 1812 central daylight time, a Cessna 152 single-engine airplane, N45973, and a Cessna 182L single-engine airplane, N974SR, collided in-flight near Noble, Oklahoma. The Cessna 152 was registered to and operated by Airman Flight School, Inc., of Norman, Oklahoma, and the Cessna 182 was registered to Mad Max Aerobatics, Inc., of Sadler, Texas, and operated by the pilot. The private pilot, sole occupant of the Cessna 152, and the commercial pilot, sole occupant of the Cessna 182, received fatal injuries. Both aircraft were destroyed. Visual meteorological conditions prevailed and flight plans were not filed for the 14 Code of Federal Regulations Part 91 flights. The pilot of the Cessna 152, on a local solo instructional flight, departed the University of Oklahoma Westheimer Airport (OUN), Norman, Oklahoma, approximately 1756. The pilot of the Cessna 182, on a personal cross-country flight destined for Sherman, Texas, departed OUN, approximately 1804.

According to radar data provided by the Oklahoma City Terminal Radar Approach Control (TRACON), after departure from OUN, the first radar return of the Cessna 152 was at 1756:17. At 1807:31, approximately 12 nautical miles (nm) southeast of the departure airport, the data depicted the start of a ground track resembling figure-eights. The altitude could not be determined for the Cessna 152.

After departure from OUN, the first radar return of the Cessna 182 was at 1804.59. The data depicted the airplane, with a 1200 beacon code, moving in a southeasterly direction toward its intended destination. The following table includes time and altitude for the Cessna 182:

TIME ALTITUDE (feet agl) 1804:59 1,300 1806:26 2,200 1807:31 2,100 1809:04 2,000 1810:31 2,000 1811:41 2,000

The last radar return from the Cessna 152 was at 1811:45, and the last radar return from the Cessna 182 was at 1811:41. At the time of the last radar returns, the targets were about 12 nm southeast of the departure airport, and the Cessna 152 was approximately 1/4 nm southeast of the Cessna 182. The Cessna 152 was heading to the west, and the Cessna 182 was heading to the southeast.

Back to Top

ACCAR Relevance



While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow heuristic tendencies to fly at cardinal thousand-ft altitudes, 2000 ft in this case. If ACCAR was applied in this scenario, the 182 would have been at about 2350 ft, instead of the 2000-ft altitude where the 152 was maneuvering in figure eight patterns. Obviously, the 152 maneuvers do not fit in the realm of cruising flight applicable to the ACCAR formula. However, the precision with which both pilots maintained the 2000-ft altitude during both cruise and pattern maneuvers was entirely inappropriate to the midair collision safety principle that all available airspace volume should be used to minimize collision target density. If just one of the two participants in a two-ship encounter is using ACCAR, then the benefit of altitude "randomization," is at least realized for the one aircraft so encouraged to deviate into less concentrated airspace located between the traditionally high density slabs of airspace.

Back to Top


Source

NTSB Identification: DCA00MA080A, DCA00MA080B; Wednesday, August 09, 2000 in Burlington TWP., NJ
Aircraft: Piper PA-31 NAVAJO: N27944
Piper PA-44 SEMINOLE: N2225G
Injuries: 11 Fatal

HISTORY OF FLIGHT: A Piper PA-31-350 Navajo Chieftain, N27944, operated by Patuxent Airways, Inc., Hollywood, Maryland, and a Piper PA-44-180 Seminole, N2225G, operated by Hortman Aviation Services, Inc., Philadelphia, Pennsylvania, were destroyed when they collided in flight over Burlington Township, New Jersey. The airline transport pilot, commercial pilot, and seven passengers aboard the Navajo Chieftain were killed, as were the flight instructor and the private pilot aboard the Seminole. Day visual meteorological conditions existed at the time of the accident, and both airplanes were operating under visual flight rules when the collision occurred. The flight crews of both airplanes were properly certificated and qualified in accordance with applicable Federal regulations. None of these individuals was experiencing any personal problems or rest anomalies that would have affected their performance. The airplanes had undergone the required inspections. Examination of their maintenance documents revealed that both airplanes complied with all appropriate airworthiness directives. Evidence gathered from the wreckage indicated that neither airplane had experienced an in-flight fire, bird strike, or structural or mechanical failure. Tissue samples revealed that the pilot of the Seminole had taken doxylamine sometime before the accident. (Doxylamine is a sedating antihistamine that has substantial adverse effects on performance.) However, the amount of blood available for analysis was insufficient for determining exactly when the pilot may have ingested the medication or whether his performance was impaired by the effects of doxylamine. A partial cockpit visibility study revealed that the Seminole would have been visible to the pilots in the Chieftain for at least the 60 seconds before the collision. No stereo photographs from a Seminole cockpit were available to determine precise obstruction angles. However, because of the relative viewing angle, the Chieftain would have been visible to the pilots in the Seminole for most of the last 60 seconds. The study further revealed that about 4 seconds before impact, or about .11 nm separation, the angular width of each airplane in each pilot's field of vision would have been approximately 0.5 to 0.6 degrees or about 1/4 inch apparent size at the windscreen.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
the failure of the pilots of the two airplanes to see and avoid each other and maintain proper airspace separation during visual flight rules flight.

full narrative excerpts

DCA00MA080A

On August 9, 2000, at 0752 eastern daylight time (all times in this brief are eastern daylight time based on a 24-hour clock), a Piper PA-31-350 Navajo Chieftain, N27944, operated by Patuxent Airways, Inc., and a Piper PA-44-180 Seminole, N2225G, operated by Hortman Aviation Services, Inc., collided in flight over Burlington Township, New Jersey. The captain, first officer, and seven passengers aboard the Chieftain were killed, as were the flight instructor and the certificated private pilot aboard the Seminole. Both airplanes were destroyed. The Chieftain was operating under 14 Code of Federal Regulations (CFR) Part 135 as a visual flight rules (VFR) charter flight for Department of the Navy personnel. The Seminole was operating under 14 CFR Part 91 as a local, multiengine airplane instructional flight. Day visual meteorological conditions existed at the time of the collision.

The Chieftain was en route from Trenton Mercer County Airport (TTN), Trenton, New Jersey, to Naval Air Station Patuxent River, Maryland. TTN air traffic control cleared the Chieftain for takeoff at 0746. At 0748, the tower controller cleared the crew to change to radio frequency 123.8 MHz (a Philadelphia Approach Control frequency), which the crew acknowledged. No further transmissions were heard from the airplane on any frequency. Impact and fire damage prevented investigators from determining the radio frequencies that had been selected by the Chieftain crew.

The Seminole departed Northeast Philadelphia Airport (PNE), Philadelphia, Pennsylvania, under VFR, from runway 24, at 0745. (PNE is located 14.5 nautical miles [nm] southwest of TTN.) Shortly after takeoff, the tower controller stated, "two five golf frequency change approved," and a crewmember responded, "two five golf." No further transmissions were heard from the airplane on any frequency. Investigators found that the Seminole's radio transmitter had been set to the COMM 2 ("communications radio 2") position. The COMM 1 switch was in the ON position, and the frequency was set to 121.70. The COMM 2 switch was in the TEST position, and the frequency was set to 126.90. PNE's ground control frequency was 121.70, and the tower frequency was 126.90.

According to airport personnel who talked to the Seminole's instructor pilot before takeoff, no practice instrument flight was to be accomplished. The president of Hortman Aviation stated that radar advisories were not normally requested during training flights. He also stated that company aircraft were supposed to fly with strobe lights on at all times. When advised that the Seminole was flying between 130 and 135 knots' airspeed when the accident occurred, the president stated that the airplane would not have been doing maneuvers at that time because that airspeed was too high.

The recorded radar data indicate that shortly before the collision, the Seminole was flying generally northeast, and the Chieftain was flying generally south. Both airplanes were flying at about 3,000 feet. About a minute before the collision, the Seminole started a gradual left turn toward the north-northeast. The last secondary radar return before the collision was received from the Seminole at 0752:37.68 at an altitude of 3,000 feet, less than .4 nm southwest of the Chieftain's last radar return. The only returns received after 0752:37.68 in the area surrounding the collision were primary returns that began to appear at 0752:42.35, near the last secondary returns associated with the Chieftain and Seminole. The loss of secondary returns and the appearance of a cloud of primary returns are consistent with loss of power to the transponders and the breakup of the two airplanes following the collision.

Back to Top

ACCAR Relevance



While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow heuristic tendencies to fly at cardinal thousand-ft altitudes, 3000 ft MSL in this case. If ACCAR was applied in this scenario, the Seminole would have been cruising at about 3200 ft, and the Chieftain would have been cruising at about 2500 or 3500 ft.


Source

NTSB Identification: MIA01FA028A, MIA01FA028B; Thursday, November 16, 2000 in Bradenton, FL
Aircraft: Lockheed-Martin F-16CG: USAF
Cessna 172N: N73829
Injuries: 1 Fatal, 1 Uninjured

HISTORY OF FLIGHT: A formation flight of two F-16s departed Moody Air Force Base in Valdosta, Georgia, on an IFR flight plan leading to the entry point for a low-altitude military training route located near Sarasota, Florida. The flight lead pilot was provided an air traffic control (ATC) frequency change from Miami Center to Tampa Approach. The flight was unable to establish communications with Tampa Approach because an incorrect radio frequency was given to the flight lead by Miami Center. The flight lead reestablished radio contact with Miami Center, cancelled the flight's IFR clearance, and proceeded under visual flight rules (VFR). The controller acknowledged the cancellation, advised the F-16 flight lead pilot of traffic in his vicinity, and asked the flight lead pilot if he wanted VFR flight following (a service that includes VFR radar traffic advisories on a workload-permitting basis.). The flight lead pilot declined. The Miami Center controller then informed Tampa Approach that the flight lead pilot had elected to terminate ATC services, but did not specify that there were two aircraft in the flight. Tampa Approach procedures did not require that the controllers use flight strips (which would have included the number of aircraft in the formation), so the Tampa controllers had no other information indicating that there were multiple aircraft present. Continuing their descent under VFR, the two F-16s assumed the "fighting wing" formation. This placed the accident F-16 on the left side of the lead aircraft and approximately 0.7 miles in trail. The accident F-16's transponder was inactive, as is normal for formation operations, making the aircraft significantly less conspicuous on ATC radar than it would be with an operating transponder. At an unknown point in the flight, the F-16 lead pilot's navigation system developed a position error and was indicating that the aircraft was several miles from its actual position. The pilot failed to recognize the error, and was attempting to visually locate the entry point for the training route based on the erroneous navigation data. Because of the lead pilot's loss of situational awareness, the two F-16s inadvertently descended into the Class C airspace surrounding the Sarasota, Florida airport without establishing required communications with ATC. Meanwhile, a Cessna 172 pilot departed Sarasota under VFR and contacted Tampa Approach. The Cessna pilot was instructed by the developmental controller receiving instruction to maintain 1,600 feet, turn left to a heading of 320-degrees, and to follow the shoreline. At 15:47:10, he was instructed to climb and maintain 3,500 feet. Miami Center contacted Tampa Approach at 15:47:55, and asked for the altitude of the F-16s. Although the Tampa controller was not in contact with the F-16s, he was able to locate the flight lead on the radar display and informed Miami that the flight lead was at 2,000 feet. A conflict alert between the lead F-16 and the Cessna activated 10 times between 15:47:39 and 15:48:03. The developmental controller stated that he heard an alarm, but could not recall where it was. The controller providing the instruction did not recall if he saw or heard a conflict alert, and no conflict alert was issued. There was no alert generated between the accident F-16 and the Cessna because the conflict alert system requires that both aircraft involved have operating transponders. The developmental controller informed the Cessna pilot at 15:48:09 that he had traffic off his left side, but received no response. The controllers were unaware of the position of the other (accident) F-16 in the formation flight. At 15:48:53, the lead F-16 transmitted, "Mayday, mayday." At 15:49:14, the flight lead pilot followed with, "Mayday, mayday, mayday, F-16 down." Examination of the wreckage of both airplanes determined that the accident F-16's left wing and cockpit area collided with the Cessna 172's right forward side (nose) and cabin area.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows: the failure of the F-16 flight lead pilot and F-16 accident pilot to maintain an adequate visual lookout while maneuvering. Factors contributing to the accident were: the F-16 flight lead pilot's decision to discontinue radar traffic advisory service, the F-16 flight lead pilot's failure to identify a position error in his aircraft's navigational system, the F-16 pilots subsequent inadvertent entry into class C airspace without establishing and maintaining required communications with air traffic control (ATC); and ATC's lack of awareness that there was more than one F-16 aircraft in the formation flight, which reduced the ATC controllers ability to detect and resolve the conflict that resulted in the collision.

full narrative excerpts

MIA01FA028A

On November 16, 2000, at 1548 eastern standard time, a U.S. Air Force F-16CG, operated by the 347th Wing, Air Combat Command, collided in mid air with a Cessna 172, N73829, near Bradenton, Florida. The F-16, based at Moody Air Force Base (AFB), Valdosta, Georgia, was on a low-altitude training mission. The Cessna 172, registered to Crystal Aero Group, was operating as a 14 CFR Part 91 personal flight. The airline transport (ATP)-rated Cessna pilot was killed. The F-16 pilot, who held a commercial pilot's certificate, ejected from the airplane and sustained minor injuries. Visual meteorological conditions prevailed at the time of the accident. The accident F-16 was part of a flight of two F-16s. A composite military instrument flight rules (IFR)/visual flight rules (VFR) flight plan was filed. The two F-16s departed Moody AFB at 1513. The Cessna 172 departed Sarasota Bradenton International Airport (SRQ) Sarasota, Florida, about 1541. No flight plan was filed.

The accident F-16 pilot, who was using call sign Ninja 2, stated that he was maintaining visual formation with his flight lead, call sign Ninja 1, when he saw a blur "like a sheet of white" appear in front of him. He stated that the airplane shuddered violently, and part of the canopy on the left side was broken away. The accident pilot stated that wind, smoke, and a strong electrical smell filled the cockpit. He stated that he called his flight lead several times, but could not hear a reply. Because the airplane was still controllable, he decided to try to reach MacDill AFB, and he began a right turn in that direction. He stated that his primary flight instruments were shattered and that he could not see them. He stated that the engine began to spool down and that he realized that he would not be able to make the airport. He stated that he turned the airplane left toward a wooded area away from a residential area and attempted an engine restart, which was not successful. When the airplane cleared the residential area, it started an uncommanded left roll. When the airplane went past a 90-degree bank angle, the pilot stated that he decided to eject. During his parachute descent, he observed the airplane "pancake" into the ground inverted and explode.

The flight lead stated that the two F-16s were assigned a block altitude of between 25,000 feet and 26,000 feet en route to the entry point of visual military training route (MRT) VR-1098. As the flight approached the SRQ area, Miami Air Route Traffic Control Center (ARTCC) cleared the F-16s to descend to 13,000 feet. At 1543:39, the Miami ARTCC controller instructed the flight lead to contact Tampa Terminal Radar Approach Control (TRACON) controllers. The flight lead was not successful (because he was given an incorrect frequency), and he reestablished contact with Miami ARTCC and canceled IFR. Miami ARTCC advised him of traffic at 10,000 feet, which was acquired on radar. The controller accepted the cancellation and asked the pilot if he wished to continue receiving radar traffic advisory services. The flight lead declined. According to the air traffic control (ATC) transcripts, the controller then stated, "radar service terminated, squawk VFR [transponder code 1200], frequency change approved, but before you go you have traffic ten o'clock about 15 miles northwest bound, a Beech 1900 at ten thousand [feet]." The flight then began a VFR descent to enter VR-1098. (For additional information see Air Traffic Control Group Chairman's Factual Report attachment to this report.)

The flight lead informed Ninja2 that they were going to perform a "G" check (G awareness maneuver). They accelerated to 400 knots, made a right 90-degree turn, followed by a left 90-degree turn back on course, and continued their descent below 10,000 feet. The flight lead then instructed the accident pilot to assume the "fighting wing" formation (with the wingman at the 7 o'clock position behind the flight lead). They continued to descend through 5,000 feet about 6 miles north of the entry point to VR-1098. The flight lead attempted to obtain a visual reference to the entry point. The flight lead also looked at his low-altitude en route chart to reference the class B airspace at Tampa and the class C airspace at Sarasota.

About 1547, the F-16 flight was heading south and descending through 4,300 feet on a converging course with N73829. Radar data indicated that the flight had overshot its intended entry point to VR-1098 and was several miles southwest of the MTR. The flight had also inadvertently passed through Tampa class B airspace without the required ATC clearance and was about to enter the Sarasota class C airspace without establishing communications with ATC, which is required by Federal regulations.

After continuing to descend, the flight lead looked back to the left and observed the accident F-16 slightly below him at the 7 o' clock position and about 4,000 feet to 5,000 feet behind him. The flight lead also observed a white, high-wing white airplane (the Cessna) in a 30 to 45-degree right turn. The Cessna and the accident F-16 collided in a left-to-left impact at the flight lead's 10 o' clock position, he stated. After the collision, the flight lead observed vaporizing fuel on the F-16's right side. The flight lead did not see the Cessna. The flight lead called the accident pilot and stated, "it appears you have had a mid air and are streaming fuel." There was no response. The flight lead began a left turn to keep the accident F-16 in sight. The flight lead saw the accident pilot bail out and the airplane collide with the ground. At 15:48:55, the flight lead stated, "mayday mayday." At 15:49:11, the flight leader stated, "mayday mayday mayday F sixteen down." At 15:50:00, the flight lead stated, "yes this is Ninja one we have an F sixteen down there is a light aircraft may have also gone down sir I am not sure." The collision occurred about 2,000 feet msl, about 6 miles southwest of the entry point for VR-1098.

A review of ATC transcripts of communications between N73829 and Tampa TRACON and communication between Miami ARTCC and Tampa TRACON indicated that N73829 contacted Tampa TRACON at 15:45:19 stating he was off Sarasota-Bradenton at 1,600 feet. At 15:45:23, Tampa TRACON told N73829 to maintain 1,600 feet. N73829 acknowledged the transmission at 15:45:30. At 15:46:59, Tampa TRACON informed N73829 to turn left to heading 320 and to follow the shoreline northbound. At 15:47:10, Tampa TRACON instructed N73829 to climb and maintain 3,500 feet, which was acknowledged by N73829 at 15:47:15.

The Miami ARTCC controller contacted Tampa TRACON at 15:47:55 and asked Tampa TRACON for the flight lead's altitude because he had lost radar contact with the lead F-16 (only the flight lead had his transponder activated because formation flights are handled as a single aircraft by ATC). Tampa TRACON replied at 20:48:00, stating "ahh hang on I see him down at two thousand." At 15:48:09, Tampa TRACON informed N73829 that he had traffic off his left side at 2,000 feet. N73829 did not respond.

A review of altitude data and ground track data (and airspace boundaries) determined that Tampa TRACON's intruder conflict detection software noted a conflict between the flight lead and the Cessna, and generated an aural conflict alert in the TRACON facility at 1547:39 that continued until 1548:03. The controller receiving instruction at the time of the accident told Safety Board investigators that he heard an alarm (conflict alert), but that he could not recall where it was. The controller providing instruction at the time of the accident stated that he didn't remember whether he saw an alert on his radar display or if he heard an aural conflict alert. He added that conflict alerts occur frequently, and that many were false. The conflict detection system did not account for the accident F-16, or a possible conflict, because it's transponder was in the standby mode.

Witnesses stated that they heard the sound of approaching jets. They observed the first jet flying south, followed by the second jet located to the left and slightly lower than the first. They also observed a small civilian airplane flying from west to east, perpendicular to the military jets. The second jet collided with the civilian airplane and initially continued southbound, according to witness statements. The second jet was observed to make a right turn, followed by a left turn. A parachute was observed, and the airplane was observed to enter a flat spin to the left before it disappeared from view below the trees. An explosion was heard, followed by heavy dark smoke rising above the terrain.

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow heuristic tendencies to fly at cardinal thousand-ft altitudes, 2000 ft MSL in this case. If ACCAR was applied in this scenario, the southbound F16s would have been cruising at about 1500 or 2500 ft, and the Cessna would have been cruising at about 2750 or 1750 ft. They would have most likely passed each other with about 250 ft of vertical flight path separation.

Another factor artificially increasing aircraft density was the shoreline that both pilots were following.

Back to Top

Source

NTSB Identification: FTW01FA025A, FTW01FA025B; Sunday, November 26, 2000 in Katy, TX
Aircraft: Cessna 172N: N6521D
Aircraft: Cessna 150E: N3588J
Injuries: 1 Fatal, 2 Uninjured

HISTORY OF FLIGHT: On November 26, 2000, at 1710 central standard time, two single-engine, high-wing airplanes, a Cessna 150E, N3588J, and a Cessna 172N, N6521D, collided while in cruise flight near Katy, Texas. The Cessna 172 sustained substantial damage and the Cessna 150 was destroyed. The Cessna 150 was registered to and operated by the private pilot, sole occupant, who sustained fatal injuries. The private pilot of the Cessna 172 and her one pilot-rated passenger, who was the registered owner and operator of the airplane, were not injured. Visual meteorological conditions prevailed for the flights, both of which were operating under 14 Code of Federal Regulations Part 91. Flight plans were not filed for either of the personal visual flight rules (VFR) cross-country flights. The Cessna 150 originated from the Easterwood Airport, College Station, Texas, and was destined for the Westheimer Airpark, Houston, Texas. The Cessna 172 originated from the San Antonio International Airport, San Antonio, Texas, at 1600, made an intermediate stop at the Fayette Regional Air Center, La Grange, Texas, and was destined for the Baytown Airport, Baytown, Texas.

According to the pilot and passenger of the Cessna 172, the pilot performed a touch-and-go landing at La Grange, and then departed for Baytown. After departure, the passenger fell asleep and the pilot continued flying the airplane toward Baytown. The pilot stated that the airplane was in level flight at 2,000 feet, approximately 10 miles west of the West Houston Airport, Houston, Texas, when she dialed in the common traffic advisory frequency (CTAF) for the West Houston Airport (123.05), intending to make a position report. As she prepared to make the report, she was scanning the area and noticed an airplane approaching her airplane from the left side at a 90-degree angle. She stated that the airplane was flying at an altitude slightly below her airplane's altitude. She initiated a climb and right turn and, subsequently, the two airplanes collided.

The passenger of the Cessna 172 awoke during the collision and realized that the airplane was in a "clockwise spiral." He assumed the controls and recovered the airplane from the spiral. He noted that the right wing was damaged and the right main landing gear had separated. The passenger stated that the airplane was difficult to control and "felt like it wanted to stall easily and spin to the right." He noticed that the flaps were extended 10 degrees and moved the flap handle to the retracted position. The airplane immediately entered an uncommanded right descending turn, and he extended the flaps back to the 10-degree position and regained control of the airplane. He then made a radio call on the CTAF for the West Houston Airport, declared an emergency and entered 7700 (emergency code) into the transponder. He announced his intentions to land at the West Houston Airport. The airport manager heard the distress call, cleared traffic from the area and gathered airport personnel to assist the pilots after they landed. The Cessna 172 touched down on runway 15, veered to the right, exited the runway surface, crossed a taxiway and came to rest upright on taxiway delta.

According to data extracted from a Garmin GPS 295 handheld navigational unit, which was being used by the pilots of the Cessna 172, the Cessna 172 was flying at an altitude of approximately 2,000 feet on an easterly heading. At 1709:58, the airplane entered a right turn. The airplane descended to 1,521 feet as it rolled through 270 degrees of the turn. It continued turning another 150 degrees and descended another 100 feet before leveling off. At 1711:11, the airplane entered a 180-degree turn to the right and descended to 961 feet before it began a climb. The airplane then maneuvered toward the West Houston Airport and landed at 1724:27.

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow heuristic tendencies to fly at cardinal thousand-ft altitudes, 2000 ft MSL in this case. If ACCAR was applied in this scenario, the eastbound 172 would have been cruising at about 2250 ft, and the southbound 152 would have been cruising at about 1500 or 2500 ft. By the design of ACCAR, they would have passed each other with about 250 ft of vertical flight path separation.

Note, "She stated that the airplane was flying at an altitude slightly below her airplane's altitude. She initiated a climb and right turn . . . the right wing was damaged and the right main landing gear had separated." Her right turn collision avoidance maneuver immediately increased the vulnerable cross sectional area of the 172 wing due to the right wing dropping below the ship centerline enough to reach down to the level of the 152 that was "slightly below her airplane's altitude." A far better collision avoidance strategy is to keep the wings pointed directly at the threat, thereby minimizing the vulnerable area of the wings; while pulling up only with elevator control to increase distance from a target slightly below. Had the 172 pilot not banked her right wing down into the path of the 152, her collision damage would have been greatly reduced, at least to her own right wing.

Back to Top


Source

NTSB Identification: FTW01FA058A, FTW01FA058B, Tuesday, February 06, 2001 at Platter, OK
Aircraft:Cessna 172P: N96621
Aircraft:Cessna 152: N114SS
Injuries: 2 Fatal, 2 Uninjured

HISTORY OF FLIGHT

On February 6, 2001, approximately 1745 central standard time, two single-engine, high-wing airplanes, a Cessna 152, N114SS, and a Cessna 172P, N96621, collided in-flight near Platter, Oklahoma. The Cessna 152 was destroyed when it impacted Lake Texoma. The Cessna 172 sustained substantial damage during the collision, and the pilot then executed a precautionary landing at the Sherman Municipal Airport, Sherman, Texas, without further incident. The Cessna 152 was registered to and operated by Southeastern Oklahoma State University, Durant, Oklahoma, and the Cessna 172 was registered to and operated by Summerlin Aviation Inc., Keller, Texas, doing business as Monarch Aviation Inc., of Addison, Texas. The flight instructor and student pilot in the Cessna 152 sustained fatal injuries. The private pilot of the Cessna 172 and his non-pilot rated passenger were not injured. Visual meteorological conditions prevailed, and flight plans were not filed for either flight, both of which were operating under 14 Code of Federal Regulations Part 91. The Cessna 152 originated from the Eaker Field Airport, Durant, Oklahoma, approximately 1730, and was operating as a local instructional flight. According to the University, the purpose of the flight was for the flight instructor to provide the student pilot instruction that consisted of pre-solo flight maneuvers. The Cessna 172 originated from the Addison Airport, Addison, Texas, at 1707, and was operating as a personal flight. According to the pilot of the Cessna 172, he departed from the Addison Airport to the north. He flew toward Lake Texoma and crossed over the Lake Texoma Spillway. He continued across the lake until approaching Oklahoma landfall and then turned the airplane toward the southeast. He maneuvered the airplane inbound to the Bonham Very High Frequency Omnidirectional Range (VOR) navigational facility, on a heading of 120 or 130 degrees. He stated that the visibility was clear with haze in the direction of the sun, which was setting. The airplane was in cruise flight at 3,500 feet and had just crossed the eastern shoreline of the lake when the pilot felt a "lump or thud," near the rear of the airplane. The pilot then felt air coming into the cabin from the left door and realized that the airplane required excessive right rudder to maintain directional control. He dialed 7700 (emergency code) into the airplane's transponder, declared "Mayday" on 121.5 and 122.8, and proceeded to the Sherman Municipal Airport, landing without further incident. The pilot added that he did not see the other airplane prior to, during, or following the collision. Multiple witnesses reported that between 1740 and 1750 they heard a "pop" or "bang" and looked to the sky. They observed an airplane "spiral" toward Lake Texoma and subsequently, impact the lake 50 yards offshore from the Platter Flats area (located along the eastern shoreline of the lake). One witness reported that he observed a "break in one of the wings" of the plane which impacted the lake. The witnesses also observed another airplane near the spiraling airplane; however; it maintained flight and flew out of their view. Two additional witnesses observed two airplanes, near the time of the accident, over Lake Texoma, that were maneuvering at altitudes just above the tree tops. The airplanes were executing "loops" and performing "wing rolls." Although neither of these witnesses observed the mid-air collision, one of the witnesses stated that these airplanes were not the airplanes that were involved in the mid-air collision. Radar data was obtained and reviewed. The Cessna 172 was tracked from the time of its departure from Addison to Platter. The radar data revealed that the Cessna 172 was in a descent just prior to the time the last radar image was received at 1741:21. The last radar image indicated that the Cessna 172 was at 2,900 feet over Lake Texoma. Radar coverage is not available in that area below 2,800 feet. At 1754:40, a series of primary radar targets were observed proceeding from the direction of the accident site toward the Sherman Municipal Airport. The radar data revealed that the target arrived at Sherman approximately 1800. There were no radar images or primary radar targets that could be identified as being the Cessna 152.

Back to Top

ACCAR Relevance

The Cessna 172 was cruising southeasterly at 3500 ft, an FAR 91.159 easterly formula altitude for the hemispherical cruising altitude regulations. The direction of the Cessna 152 is not listed in the accident report. No radar targets were painted for the 152 to determine its position history or direction of travel. In any case, if the 172 had been using ACCAR, it would have been at about 3350 ft and would have missed the 152 by at least 100 ft. If the 152 was maneuvering in non-cruising flight, it may have coincidentally been at 3500 ft as a simple pilot prerogative to be at any altitude while maneuvering. In that case, the pilot may have been attracted to 3500 ft as a "cardinal altitude" attraction for getting the 100-ft hand of the altimeter pointing straight down for heuristic tracking of some consistent operating point on the altimeter scale. Any such concentrations of aircraft at any fixed altitude tends to overly concentrate aircraft into unnecessarily narrow slabs of high-density airspace. The heuristics of flying level with the 100-ft hand of the altimeter at any up or down orientation for whatever reason by large numbers of pilots should be recognized universally as a risk multiplying altitude selection strategy. Random altitudes provided by ACCAR to pilot's on random headings are far superior to any heuristic selections of "100-ft-hand-up" or "100-ft-hand-down" altitudes that unnecessarily concentrate aircraft at limited numbers of cruising altitudes.

Back to Top


Source

NTSB Identification: FTW01FA058A/FTW01FA058B, Thursday, February 15, 2001 in Long Beach, CA
Aircraft: Cessna 152: N68763
Aircraft: Cessna 172N: N4686G
Injuries: 4 Fatal

HISTORY OF FLIGHT: A midair collision occurred between the Cessna 152 and a Cessna 172, which were flying between 800 and 1,000 feet above the ocean in an established student training practice area. The flight instructors and their respective students lost control of their airplanes, which descended into the ocean and sank. An eyewitness in a ship observed the airplanes seconds prior to the collision. The witness stated that "one plane appeared to bank and turn directly into the other plane." Another witness, who was airborne in a helicopter, reported that before the impact he had observed one of the airplanes performing counterclockwise orbits, like a turn about a point ground reference maneuver. This airplane had completed several circles when it collided with another airplane that was flying in a westerly direction. Neither the Cessna 152's empennage nor the Cessna 172's engine was recovered. Radar tracks for the airplanes could not be determined. The collision occurred in a near head-on trajectory, based upon the severity of the impact damage to the leading edge of the Cessna 152's right wing, the lack of impact damage in the Cessna 172's aft fuselage and empennage, the witness statements, and the locations where the airplanes were found (the Cessna 152 was west of the Cessna 172).

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

The failure of the flight crews of both airplanes to maintain adequate visual lookout for traffic.

full narrative excerpt

LAX01FA101A

On February 15, 2001, about 1540 Pacific standard time, a midair collision occurred between a Cessna 152, N68763, and a Cessna 172N, N4686G, over the Pacific Ocean about 6 nautical miles (nm) south of the Long Beach Municipal Airport, Long Beach, California. Witnesses reported that following the collision both airplanes entered uncontrolled descents, impacted the water, and sank. The airplanes were rented from and operated by the same flight school, the Long Beach Flying Club & Flight Academy, and were destroyed. In each airplane a Long Beach Flying Club certified flight instructor (CFI) and a student sustained fatal injuries. Visual meteorological conditions prevailed, and no flight plans were filed. The airplanes were operated under the provisions of 14 CFR Part 91 as instructional flights. The Cessna 152 departed from the Long Beach airport about 1513, and the Cessna 172 departed 13 minutes earlier.

At the time of the midair collision, a ship captain was located about 0.6 nm south of the entrance to the Long Beach harbor's eastern breakwater gate. The captain reported that he observed two airplanes flying about 0.3 miles south of the gate. He stated "one plane appeared to bank and turn directly into the other plane." Thereafter, they both descended into the water.

Several additional crewmembers on the ship with the captain also observed the collision. In summary, one crewmember verbally reported that the airplane flying westbound was smaller than the other airplane. Another crewmember reported that he believed one of the airplanes collided with the other airplane's tail section. After the collision, one of the airplanes spiraled out of control in an easterly direction, while the other airplane dove straight into the ocean on the west side of the channel.

An air taxi helicopter pilot, who was located near the Queen Mary, and who was departing with passengers for a southbound flight to Catalina, also observed the midair collision. The pilot reported that he observed two similar airplanes flying in the vicinity of the breakwater. One of the airplanes was performing counterclockwise orbits, like a turn about a point ground reference maneuver. This airplane had completed several circles over the same area. The other airplane was flying westbound in straight and level flight. However, the air taxi pilot indicated that he had only observed this airplane for 1 second before the impact occurred. The airplanes were between 800 and 1,000 above the ocean when they collided about 1540.

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow heuristic tendencies to fly at cardinal thousand-ft altitudes, 1000 ft MSL in this case. If ACCAR was applied in this scenario, the westbound aircraft would have been cruising at about 500 or 1500 ft, and the circling aircraft could have been cruising at any randomized altitude away from the heuristically attractive cardinal values, such as 1000 ft, 2000 ft, etc. Another factor artificially increasing aircraft density was the scenic harbor and shoreline that may have been systematically attractivng both pilots into artificially high density airsspace.

Back to Top


Source

NTSB Identification: ATL01LA063A/ATL01LA063B, Saturday, June 02, 2001 in Anguilla, MS
Aircraft: Air Tractor 502B: N257LA
Aircraft: Cessna 188B: N731KG
Injuries: 2 Fatal

HISTORY OF FLIGHT: Two agricultural airplanes, an Air Tractor 502B and a Cessna 188, collided in flight at low altitude over a field. The Cessna was working a field, and the Air Tractor was ferrying between aerial application sites when the collision occurred. Examination of both wreckage revealed that the right wing of the Cessna collided with the right elevator of the air tractor. The collision altitude was not determined. The right -a-way rule states that the airplane to the right has the right-a-way. Valium was also detected in tissue samples from the Air tractor pilot. The sun position limited the visibility of the Cessna pilot.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows: Failure of both pilots to maintain visual lookout, resulting in an in-flight collision. The air tractor pilot operated the positioning flight at an altitude below 500 feet agl. Valium was detected in the toxicological examination of the Air Tractor pilot.

full narrative excerpt

ATL01LA063A

On June 2, 2001, at 0800 central daylight time, an Air Tractor 502B, N257LA, and a Cessna 188, N731KG, collided in flight two miles north of Anguilla, Mississippi. The agricultural flights were operated by Nick's Flying Service, Inc., and Anguilla Flying Service, Inc., respectively, under the provisions of Title 14 CFR Part 137. Visual meteorological conditions prevailed at the time of the accident. Both airplanes were destroyed, and the Cessna was consumed by post-crash fire. Both commercial pilots were fatally injured. The Air Tractor departed a private airstrip at Rolling Fork, Mississippi, about 0735, and the Cessna departed a private airstrip in Anguilla, Mississippi, about 0750.

According to information recovered from Anguilla Flying Service, Inc., the Cessna had departed the private airstrip about 10 minutes before the accident, and was spraying a field adjacent to the east side of the field over which the collision occurred. The review of information from the operator revealed that the Cessna appeared to have been on a easterly heading for the initial swath run to a field about 500 feet east of the in-flight collision.

According to information recovered from Nick's Flying Service, Inc., the Air Tractor had completed an aerial application operation to a field four miles north of the accident site, and was enroute to another field miles south of the accident site. Reportedly, the Air Tractor, the Air Tractor was flying enroute at a low altitude between the two locations, and the south bound direct flight path placed the airplanes over the accident site. The altitude at which the collisions occurred was not determined, however the Cessna was operating in accordance with FAR Part 137.49 for altitude and object clearance.

The sun inclination and azimuth for the accident location was 48.8 degrees inclination at 93.2 degrees.

A review of the Federal Aviation Regulations disclosed that when converging airplanes at the same altitude, the airplane to the right has the right -a-way. The FARs further states that the minimum safe altitude over other than congested areas is 500 feet above the surface except over sparsely populated areas, and in those cases the aircraft may not operate closer that 500 feet to any person, vessel, vehicle, or structure (FAR Part 91,113, 91.119).

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow tendencies to fly at altitudes that have artificially and unnecessarily high aircraft threat concentrations. If ACCAR was applied in this scenario, the southbound cruising Air Tractor would have been at about 500 or 1500 ft, and the Cessna could have been maneuvering as expected in close proximity to the ground as needed for the aerial application maneuvers required for the job at that site. Expecting a pilot maneuvering mere feet above the ground to be simultaneously looking out for other very low altitude collision threats is not quite fair of any other pilot unnecessarily picking the same ground hugging altitude slab for routine cruising. This accident bears much similarity to the Burly, Idaho, accident July 16, 1998. Aerial applicators are frequently observed in cruise transit beween loading-refueling sites and customer fields for relatively long durations at altitudes just over treetop and powerline level. If all aerial applicators do this (as it appears they usually do), their inherent midair collision safety is not much better than high-speed boats on a lake; all flying at about the same elevation. Given the likelihood of bug splattered windshields and low angle sunshine in the early morning hours when light wind conditions are most conducive to accurate aerial application, flying in artificially high density airspace in close proximity to the ground with all of your other coworkers and competitors is quite simply a recipe for disaster. The relatively minimal cost penalty for climbing above the lake-like lowest possible cruising altitude up to the first ACCAR formula altitude is a very cheap insurance policy well worth the cost of the safety advantage provided by ACCAR.

Back to Top


Source

NTSB Identification: NYC01WA159A/NYC01WA159B, Wednesday, June 20, 2001 in Uxbridge, Canada
Aircraft: Cessna 170B: C-GKGG
Aircraft: Robinson R-22: C-FFFM
Injuries: 1 Fatal, 1 Minor

HISTORY OF FLIGHT: On June 20, 2001, about 1950 eastern daylight time, a Cessna 170B, C-GKGG, received minor damage, and a Robinson R-22 helicopter, C-FFFM, was destroyed after a midair collision near Uxbridge, Ontario, Canada. The non-certificated Canadian pilot of the Cessna received minor injuries, while the Canadian certificated commercial pilot of the Robinson was fatally injured. Visual meteorological conditions prevailed and no flight plan was filed for either aircraft. Both flights were conducted under Canadian Regulations.

According to a Transportation Safety Board of Canada investigator, the Robinson was on a positioning flight from the Lindsy Municipal Airport, Lindsy, Ontario, destined for the Buttonville Airport, Buttonville, Ontario. The Cessna had departed from a private grass strip near Sandford Sideroad, Uxbridge, about 1945, and proceeded southbound. About 800-1,000 feet above the ground, the pilot of the Cessna observed the Robinson in front of him and attempted to avoid a collision. The Cessna struck the Robinson's rotor system, and the helicopter descended to the ground, coming to rest inverted in a field on the south side of Sandford Sideroad. The Cessna pilot performed a forced landing to a field on the north side of Sandford Sideroad.

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow tendencies to fly at altitudes that have artificially and unnecessarily high aircraft threat concentrations. If ACCAR was applied in this scenario, the southbound cruising Cessna would have been at altitudes such as 1500, 2500, etc., and the Robinson headed southwest would have been at altitudes such as 1625, 2625, etc. Using ACCAR, the two flight paths would have been about 125 feet apart. Many pilots routinely fly 1000 ft above ground level for minimal terrain clearance, which is the USA FAR minimum altitude for operations in populated areas. Flying at the lowest legal limit, where many others of like mind may be, is just one more systematic way of artificially and unnecessarily increasing aircraft collision target density.

Back to Top


Source

NTSB Identification: DCA02RA047A, DCA02RA047B, Monday, July 01, 2002 in Uberlingen, Germany
Aircraft: Tupolev TU154, registration: RA-85816
Aircraft: Boeing 757-23F, registration: A9C-DHL
Injuries: 71 Fatal

HISTORY OF FLIGHT: On July 1, 2002, about 2335 local time, a Boeing 757-200, Bahrain registration A9C-DHL, operating as DHL flight 611, and a Bashkirian Airlines Tupolev TU154, Russian registration RA85816, collided in midair over Uberlingen, Germany. The two flight crewmembers onboard A9C-DHL suffered fatal injuries. Twelve crewmembers and 57 passengers onboard RA85816 also suffered fatal injuries.

By NBC’s Judy Augsburger in Moscow, Andy Eckardt in Ueberlingen, The Associated Press and Reuters contributed to this report, July 2, 2002

SWISS AIR TRAFFIC controllers said the pilot of the Tupolev 154 passenger jet carrying Russian children to a holiday in Spain from Moscow received warnings to reduce altitude before colliding with the plane operated by the courier company DHL European Air Transport. But the suggestion by the Swiss authorities infuriated Russians, especially because it came before investigators had an opportunity to analyze the aircraft flight recorders, which were recovered on Tuesday. Sergei Rudakov, A Russian aviation official, denied the pilot of the Bashkirian Airlines aircraft had caused the collision late Monday night and suggested it was perhaps the other plane’s pilot. He spoke on a report broadcast on Russia’s RTR television. Andrei Tepanyok, the airline’s director, told NBC News that the aircraft was the newest plane in the fleet, built in 1995, and was equipped with all modern systems required to fly in Europe, including anti-collision systems. Tepanyok asserted that the crew was very experienced.

RESCUE THROUGH THE NIGHT

Meantime, rescue crews in helicopters using infrared cameras worked through the night in search of bodies or survivors, and hundreds of people searched the low rolling hills around Lake Constance. The lake, bordered by Austria, Germany and Switzerland, is one of Europe’s biggest, and is a popular vacation spot. More than 800 rescue workers were spread across the 20-mile-wide crash site Tuesday. By daybreak, 12 bodies had been recovered, and investigators had located the flight data recorder from the Tu-154, as well as smoldering pieces of both aircraft. Even though none of the parts were believed to have fallen into Lake Constance, 22 boats patrolled the waters looking for wreckage. The region is on Germany’s border with Switzerland and Austria, about 135 miles south of Frankfurt. The Tu-154 was carrying a group of children and teen-agers from Bashkorstotan, a Russian republic in the southern Ural Mountains. Tuesday, Wednesday and Thursday were set aside for mourning in Bashkortostan.

Russian President Vladimir Putin sent his condolences to the relatives of the victims, and dispatched investigators and the Russian general consul in the Germany city of Bonn to the crash scene. Russian officials at the emergency situations ministry and the tour agency that helped organize the trip said eight of the children were younger than 12. Forty-four of the children were between 12 and 16 years old.

THREE REQUESTS

The DHL plane, a Boeing 757, was en route from Bahrain to Brussels, according to the company’s Web site. Swiss air traffic controllers repeatedly asked the Tu-154 pilot to lower his altitude, but he did not respond, said Ulrich Mueller, the Baden-Wuerttemberg state transport minister. The DHL plane changed course, but it was too late to avoid the crash late Monday night, Mueller said. Anton Maag, chief of the air traffic control tower in Zurich, said the air traffic controller — described as a very experienced member of staff — gave the first descent order to the Russian plane about two minutes before the collision. “This is normally sufficient,” he said. But the Russian plane only began to decrease altitude after a third request, Maag said. At the same time, the DHL plane’s automatic collision warning system inexplicably issued an order to descend, and pilots are obliged to immediately follow these instructions, Maag said.

At Moscow’s Domodedovo airport, Bashkirian representative Sergei Rybanov said 52 children, five adults and 12 crew were aboard the Russian plane. All flew into Moscow’s Sheretmeyevo airport on Saturday, but when they missed their connection requested that the airline organize a special flight to Barcelona. Axel Gietz, head of DHL corporate affairs in Brussels said both people aboard the cargo jet, the British pilot, Paul Phillips, and his Canadian co-pilot, Brant Campioni, were killed. Another DHL spokesman, speaking on condition of anonymity, said their aircraft was built in 1990 and purchased by his company in 1999 from British Airways, which had used it as a passenger jet. It was equipped with a traffic collision avoidance system and had been subject to regular inspections and maintenance like all the company’s planes, he said. Authorities said nobody on the ground was harmed.

THUNDER IN THE AIR

Witnesses said they heard a noise like thunder and saw a fireball erupt in the night sky, then saw large and small pieces of wreckage falling to the ground and into Lake Constance. Scattered fires were sparked in the rural area, but there were no casualties on the ground, authorities said. Dirk Diestel, 47, was changing his child’s diaper shortly before midnight when he looked up through a skylight and saw a huge fireball in the sky. “Immediately I thought that something horrible had happened,” he said. The three-engine Tu-154, first put into commercial service in 1972, is the workhorse of Russia’s domestic airlines and widely used throughout the former Soviet Union and Eastern Europe, as well as in China.

This three-engine aircraft was first put into commercial service in 1972. It is widely used in Russia and throughout the former Soviet Union. Two turbofan engines are located on either side of rear fuselage, and third is in the extreme rear fuselage with an intake at the base of the fin.

Crew of three; two pilots and flight engineer, with provisions for navigator and five cabin staff. Two passenger cabins, separated by service compartments; alternative configurations for 166 tourist-class passengers or for 134 tourist and 12 first-class passengers. Wingspan: 123 feet Length: 157 feet Fuselage diameter: 12.5 feet Max. payload: 39,680 lb Controls: Conventional and power-operated Max. Altitude: 39,000 feet Range (w/ max payload): 2,299 miles Cruising speed: 581 mph

Back to Top

ACCAR Relevance

The combination of takeoff and destination airports shows that the two aircraft were cruising level at 36,000 ft on perpendicular flight paths (Moscow to Barcelona crossing Bahrain to Brussels). Aircraft using ACCAR would have been separated by over 200 ft. Human intervention by air traffic controllers, and the pilot evasive action in response to $35,000 per aircraft collision prediction instruments, were totally ineffective at preventing the collision. While airborne collision prediction instruments ordered both pilots to take the correct evasive action, an ATC controller order contradicting a technically valid automatic TCAS instruction caused both aircraft to dive into each other. Such human failures by ATC personnel are not common.  However, they are expected, and occur at the rate of hundreds per year in USA airspace alone.

Had both aircraft been accurately obeying the ACCAR formula, there would have been no compelling need for a verbal warning from the Swiss air traffic controllers to avoid the midair collision (other than to establish a more comfortable path crossing altitude safety margin). Russ Paielli's paper (http://web.wt.net/~b1rd/RussPaielliFinalPaperFall2000AirTrafficControlQuarterly.pdf)proves that experienced airline pilots using Flight Management Systems (FMS, a computer-coupled autopilot) routinely maintain accurate enough altitudes for this assertion. Additionally, had both aircraft been obeying ACCAR, the airborne collision prediction instruments of the higher aircraft would have ordered a climb, while the instruments on the lower aircraft would have ordered a dive, increasing the safety margin at the crossing of their paths with no intervention from air traffic controllers.

This collision shares common themes with the Namibian collision September 13, 1998, between another Tu-154 and a US Air Force C141 Starlifter. Both involved at least one human error by one flight crew. Neither was prevented by the intervention of air traffic controllers. Neither was prevented by airborne collision prediction instruments. Both could have been prevented by universal adoption of ACCAR at the level of accuracy currently used by pilots following the hemispherical cruising altitude rules. In both cases, to a high degree of certainty, if only one pilot was using ACCAR, the the probability of survival would have been far greater because their flight altitude would not have been limited to very thin slabs of legal airspace, instead of the full volume of airspace allowed by ACCAR.

The German midair accident also shares a generic systematic failure mode with one that almost occurred January 31, 2001, near Yaizu NDB, off Shizuoka Prefecture, Japan (http://aviation-safety.net/database/2001/010131-3.htm). The ATC controller issued an order to a climbing aircraft to descend almost immediately before the TCAS gave a conflicting climb instruction to that same pilot. Simultaneously, TCAS was giving the other pilot an order to dive. As in Germany, both pilots were diving to avoid each other, while one had been ordered by TCAS to climb, in contradiction of the ATC order to dive. At the last moment, the pilot with conflicting climb-descent orders descended abruptly, injuring about 100 passengers and crewmembers, with a vertical clearance to the other aircraft of 20-60 meters. In any case, nothing in the ATC and TCAS system was operational to maintain flight safety. The human ATC and pilot factors were systematically designed to permit undesirable single failure actions sufficient to allow a midair collision, which would have killed 427 passengers and crewmembers, while destroying a 747-446D and a DC-10-40. While ACCAR would have had no particular significance in preventing this particular Japanese midair collision (because both aircraft were not cruising prior to the first avoidance maneuver), the systematic human failures in Japan were virtually identical to those allowing the German midair collision.

In summary, nothing in the ATC-TCAS system prevents midair collisions between cruising aircraft that could otherwise be saved by ACCAR.

Back to Top


Source

NTSB Identification: MIA03FA007A/MIA03FA007B, Sunday, October 27, 2002 in Coral Springs, FL
Aircraft:Cessna 172M, registration: N9840V
Aircraft:Cessna 172N, registration: N6101F
Injuries: 2 Fatal, 2 Uninjured

HISTORY OF FLIGHT

On October 27, 2002, about 1330 eastern standard time, a Cessna 172M, N9840V, registered to Power Systems LTD, Inc., and operated by American Flying Club Inc. as a Title 14 CFR Part 91 instructional flight, and a Cessna 172N, N6101F, registered to a private individual, and operated by Airborne Systems Inc., as a Title 14 CFR Part 91 instructional flight, collided while in cruise flight in Coral Springs, Florida,. Visual meteorological conditions prevailed, and no flight plans were filed for either flight. N9840V was destroyed, and the private-rated dual student and the commercial-rated flight instructor in N9840V received fatal injuries. N6101F incurred substantial damage, and the private-rated dual student and the commercial-rated flight instructor in N6101F received no injuries. Both flights originated from Fort Lauderdale Executive Airport, Fort Lauderdale, Florida, the same day, about 1245.

According to the dual student in N6101F, he and his flight instructor had been flying in the practice area west of Fort Lauderdale, Florida, and they had performed "8's on pylons and lazy 8's", as part of the commercial maneuvers training in pursuit of an FAA commercial pilot certificate. The student said he was the pilot flying N6101F, and they were proceeding southeast bound at an altitude of 2,000 feet, on a 120-degree magnetic bearing to the "WSBR 740 AM radio tower. As they neared the "740 tower", he said they were receiving needle fluctuations on N6101F's ADF indicator, indicative of them being very close to the tower, when all of a sudden, an airplane appeared very close, in the right corner of their airplane's windshield, having come from behind the blind spot created by their airplane's right wing. He said it looked as if the pilot of the other airplane saw them about the same time, and thinks that both he and the other pilot immediately initiated right turns in an attempt to avoid the other. The student further stated that as he initiated the right turn, the other airplane appeared to effectively travel across his airplane's wind shield from right to left, remaining just above the glare shield covering his airplane's instrument panel. He said he then felt the impact of his airplane's left wing colliding with some portion of the other airplane, and his airplane "tumbled", and entered a spin to the left. During the spin, he said he saw another airplane about 250 to 300 feet below him, and it appeared to be inverted. The instructor took control of N6101F from the student, made emergency communication transmissions to advise others of the situation, and affected an emergency landing to a dirt road paralleling the then busy Sawgrass Expressway. The other airplane in the collision, N9840V impacted a dirt road in a rock quarry in the vicinity of the Loxahatchee National Wildlife Refuge, in unincorporated Palm Beach County, and was destroyed on impact.

Back to Top

ACCAR Relevance

These two aircraft collided while in cruise flight at 2000 ft MSL in visual meteorological conditions (VMC). The hemispherical cruising altitude rules of 91.159 do not apply below 3000 ft above ground level (AGL), where random altitude cruising is legal. For human factors reasons, legal pilots below 3000 ft AGL tend to fly in cruise at non-random altitudes, typically with the 100-ft altimeter hand either straight up (usually) or straight down. This natural behavior artificially and unnecessarily concentrates aircraft in narrow bands of high-density airspace. This artificially high concentration maximizes collision probability because of the target density term in the mean free path formula. In other words, the higher the target density, the greater the collision probability (see section 4.2 of "U.S. Aviation Regulations Increase Probability of Midair Collisions", Risk Analyis: An International Journal, April 1997).

While random altitude cruising is legal below 3000 ft AGL, and while random altitude cruising is far safer than any formula altitude calculated by the hemispherical cruising altitude rules, these Florida pilots were not cruising at the far safer random altitudes. They were naturally, yet unwisely, cruising in an artificially high density, self-limited volume of airspace centered on 2000 ft, while wasting the legal volume between integer-thousand-ft levels that could have been used to minimize collision target density.

Due to the premature Federal Aviation Administration (FAA) denial of request for Notice of Proposed Rulemaking 28996, these pilots were denied the wisdom of a mathematically far superior option of cruising under the Altimeter-Compass Cruising Altitude Rule (ACCAR) modeled as RP-1000 in the April 1997 issue of Risk Analyis. As such the FAA denial of 28996 qualifies under fundamental risk analysis definitions as a root cause contributor to this accident. The FAA had peer-reviewed, documented proof from the Risk Analysis article that a far superior alternative to non-random altitude cruising was available at no cost to aircraft owners and pilots. By the time of this accident, the FAA knew, or should have known, of the corroborating conclusions of a NASA air traffic control programmer, Russ Paielli, who came to the same conclusion in his own independent peer-reviewed article published in Air Traffic Control Quarterly. The failure to take corrective action for a know safety defect or safety shortcoming places normal business corporations at great risk for financial losses in liability lawsuits. The heavy dependence of the FAA on its governmental immunity inspires it to have no interest in the concerns of NPRM 28996 because such safety issues "do not address an immediate safety concern". While the largely ground-based FAA personnel almost never have an "immediate safety concern" for the risk of a midair collision, by the time pilots are at risk of a midair collision, it is too late to tell them how their actions unwittingly contribute to an unnecessarily high midair collision probability. The "budgetary constraints" referred in this letter do not contribute to a valid defense against the moral (and for commercial corporations, the legal) obligation to correct a known safety deficiency in the information and regulations provide to pilots. If the FAA had provided this information to pilots back in 1998, then ACCAR could have been used in 2002 to avoid the Florida midair collision at no cost to the aircraft owners or pilots.

Notice in the NTSB account where the surviving student pilot reported that he had initiated a collision-avoidance right turn, and that the other aircraft apparently had also notice the threat at the last second and initiated a similar right turn. The mean free path formula has a cross-sectional area term (see section 4.2 of Risk Analyis) that mathematically multiples collision probability in proportion to the vulnerable outline or "shadow" area seen by an observer of the threatening collision. Two level head-on aircraft present the minimum cross-sectional area for damage. If either aircraft is banking in a collision avoidance maneuver such that the parallel orientation of the wings is lost, then the collision-vulnerable cross-sectional area increases greatly. Two banking aircraft can easily have three times the vulnerable overlapping area (and risk) of two aircraft with parallel wings. Two small aircraft in wings-perpendicular banking turns need to have a center-to-center offset of over 20 feet to avoid a collision. In contrast, parallel-wings aircraft may miss each other with as little center-to-center offset as eight feet to cross paths without colliding. If the lessons of the Risk Analysis article had been properly communicated to pilots by the FAA in 1998, then pilots in 2002 could have known by the mean free path formula that it is far better to use wings-parallel evasive maneuvers to reach a safe-enough eight-foot separation much sooner than the 20-foot separation required for safety in a "T"-crossing, wings-banking maneuver. Often, there isn't time to initiate a banked turn. Simply climbing assertively with a high positive acceleration, or diving with a gentle negative acceleration, results in a far better collision-avoidance strategy. (Most aircraft are designed to withstand far more upward acceleration stresses, compared to the alternative of negative "g" maneuvers.)

Back to Top


Source

NTSB Identification: DEN03MA035A/DEN03MA035B, Friday, January 24, 2003 in Denver, CO
Aircraft: Piper PA-31T, registration: N360LL
Aircraft: Cessna 172P, registration: N52241
Injuries: 5 Fatal, 6 Injured

HISTORY OF FLIGHT (Preliminary Report)

On January 24, 2003, at 1722 mountain standard time [sunset was 1710], a Cessna 172P, N52241, registered to and operated by EDB Air, Inc., of Englewood, Colorado, and a Piper PA-31T, N360LL, registered to and operated by Lee Larson Aircraft Sales of Northglenn, Colorado, collided in midair over, Denver, Colorado. The private pilot and two passengers aboard N52241 and the two commercial pilots aboard N360LL were fatally injured. Denver police reported six persons on the ground, including a 15-year old boy and a 2-year old girl, receiving minor injuries from falling debris. Visual meteorological conditions prevailed, and no flight plans had been filed by either pilot for the flights being operated under Title 14 CFR Part 91. N52241 originated at Centennial Airport at 1700 and was en route to Cheyenne, Wyoming. N360LL originated at Jeffco Airport, Broomfield, Colorado, at 1710 and was en route to Centennial Airport.

Preliminary information indicates both airplanes were operating outside of Denver's Class B airspace. At the time of the accident both aircraft were in Class E airspace. At 1710, the pilot of N360LL (Piper PA-31T) departed the Jeffco Airport while flying under visual flight rules (VFR) toward the southeast. At 1717, the pilot contacted the Denver Air Traffic Control (TRACON) and advised he was in bound to Centennial Airport. The controller assigned the pilot a beacon code of 5250 and radar identified the airplane about four miles south of the airport. The controller advised the pilot he was not receiving a Mode C transponder altitude signal and asked if he was squawking altitude. The pilot responded with "yes sir we are." The controller then requested that the pilot to verify his altitude, and the pilot advised that he was at 7,800 feet. N360LL's ground speed indicated 230 knots at this time.

At 1710 the pilot of N52241 (Cessna 172) departed the Centennial Airport VFR northbound and later contacted the Denver TRACON at 1718. The pilot advised that he was enroute to Cheyenne at 7,300 feet, and he requested clearance to fly at 8,500 feet. The controller assigned a beacon code of 5251 and radar identified the airplane 15 miles southeast of Jeffco Airport. The controller cleared the pilot to enter the Class B airspace and on course at 8,500 feet. N52241's ground speed indicated 110 knots at this time. The controller then asked the pilot of N360LL (Piper PA-31T) to say altitude. The pilot responded with 7,600 feet, and the controller issued a traffic advisory to N360LL that there was traffic at the pilot's 12 o'clock position and 1 mile, a Cessna at 7,600 feet. There was no acknowledgement from the pilot of N360LL. The collision occurred 2.5 minutes after the pilot of N360LL had contacted the Denver TRACON controller.

Witnesses said they saw the two airplanes collide head-on. One witness said N360LL made an evasive maneuver, a sharp left bank, at the last second. After the collision, N360LL entered an inverted flat spin and fell into the backyard of a residence in the 3200 block of W. 26th Ave. N52241 descended nose down and struck an unoccupied house in the 3400 block of W. Moncrieff Pl. in the Highland neighborhood. The impact ruptured a natural gas line, causing an explosion that blew out the walls of the house and collapsed a portion of the roof.

The on-scene investigation revealed the majority of N52241's wreckage was in the house. The outboard portion of N360LL's right wing, with tip tank still attached, was located in the backyard of a residence near 26th Ave. and Irving St. The horizontal stabilizer, with the right leading edge aft to the spar missing, struck a parked auto. The right engine, with attached propeller, was located in the 3100 block of W. 25th Ave. The debris path covered roughly a 24 square block area.

The Operational Factors Division (AS-30) from the NTSB Headquarters is assisting the investigation.

Final Report Summary

A Piper PA-31T "Cheyenne" and a Cessna 172P "Skyhawk" collided in midair during cruise flight at dusk and in visual meteorological conditions. The Cheyenne departed under visual flight rules (VFR) from a local airport northwest of Denver, and was proceeding direct at 7,800 feet to another local airport south of Denver. Radar indicated its ground speed was 230 knots. Its altitude encoder was transmitting intermittently. The Skyhawk departed VFR from the south airport and was en route to Cheyenne, Wyoming, at 7,300 feet. The pilot requested and was cleared to climb to 8,500 feet and penetrate class B airspace. Radar indicated its ground speed was 110 knots. The Skyhawk was flying in the suggested "VFR flyway"; the Cheyenne was not. When the controller observed the two airplanes converging, he asked the pilot of the Cheyenne for his altitude. He replied he was at 7,600 feet. The controller immediately issued a traffic advisory, but the pilot did not acknowledge. Both airplanes departed controlled flight: the Skyhawk struck a house, and the Cheyenne fell inverted into the backyard of a residence. Wreckage was scattered over a 24 square block area in west Denver. At the time of the accident, the controller was handling low altitude en route, arrival and departure traffic for both airports. Wreckage examination disclosed four slashes, consistent with propeller strikes, on top of the Cheyenne's right engine nacelle, the cabin above the right wing trailing edge, the empennage at the root of the dorsal fin, and at the tail cone. The Cheyenne was on a similar flight three days before the collision when the pilot was informed by air traffic control that the transponder was operating intermittently. According to recorded radar and voice communications from that flight, the transponder/encoder operated intermittently and the pilot was so advised. Examination of the Cheyenne's altimeter/encoder revealed a cold solder connection on pin 8 of the 15-pin altimeter connector. When the wire was resoldered to the pin, the information from the altimeters, encoder, and altitude serializer was normal.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

Both pilots' inadequate visual lookout. A contributing factor was the Cheyenne pilot operating the airplane with a known transponder deficiency.

See full narrative of the final report. Excerpts copied below:

At 1718:58, the pilot of N52241 contacted Denver Terminal Radar Control (TRACON): "Denver, Cessna Five Two Two Four One is over Denver at seven thousand, three hundred feet, with a request." The controller issued the pilot a transponder beacon code of 5251. The pilot acknowledged the instruction and requested clearance to climb to 8,500 feet, which would place the airplane in Class B airspace. He also advised he was en route to Cheyenne. [At this point, Centennial tower called the controller with a request for another aircraft's IFR departure release. The controller issued the release and assigned a departure heading of 050 degrees, then coordinated the departure with the south sector controller]. At 1720:04, the controller identified the airplane on radar when it was 15 miles southeast of Jeffco Airport, and asked the pilot to repeat his requested altitude. He repeated his request for 8,500 feet. [At this point, separation between N360LL and N52241 had closed to 2.91 miles. N52241's radar-computed ground indicated "11," or 110 knots. At about this time, the controller made a transmission to an aircraft that was on the downwind leg at Centennial Airport. He then vectored another airplane onto the NDB (nondirectional beacon) approach to Centennial Airport. The controller was also monitoring other aircraft that were getting close to a restricted area and the airport traffic area]. At 1720:16, the controller cleared N52241 to enter class B airspace and climb to 8,500 feet. Two seconds later, radar showed target separation as 1.64 miles. At 1720:22, target separation was 1.20 miles. At 1720:27, target separation was 0.80 miles.

At 1720:28, the controller asked the pilot of N360LL to report his altitude. The pilot replied, "(Unintelligible) six." The controller said, "Say again." At 1720:31, target separation had reduced to 0.29 miles. The pilot said, "Seven thousand, six hundred." At 1720:33, the controller issued the pilot a traffic advisory: "Traffic is at twelve o'clock and a mile at seventy seven hundred, a Cessna." The pilot did not acknowledge this transmission. At 1720:36, the two airplanes were 0.06 miles apart. Immediately thereafter, radar data indicated both targets had entered "coast" mode (i.e. computer-generated projection of targets' tracks and positions). At 1720:47, the controller advised N360LL that the previously reported traffic was no longer a factor and issued another advisory for traffic 4 miles away. Receiving no reply from the pilot, the controller attempted several times to contact both airplanes. The controller then contacted a traffic patrol pilot and asked him to fly over the area where radar contact was lost. Shortly thereafter, the traffic patrol pilot reported that it appeared there had been an accident. The TRACON controller initiated search and rescue procedures.

In addition to controlling IFR traffic, all commissioned radar facilities provide safety alerts, traffic advisories, and limited radar vectoring (on a workload permitting basis) to VFR aircraft. This does not relieve the VFR pilot from his responsibility of seeing and avoiding other traffic (chapter 4, section 1, paragraph 17).

According to 91.117(c) of the Federal Aviation Regulations (FAR), the speed limit for aircraft operating in the airspace underlying Class B airspace, or in a VFR corridor through such airspace, is 200 knots (230 mph).

FAR 91.215(b)(2) states that aircraft operating within 30 nautical miles (of Denver International Airport) at altitudes from the surface up to 10,000 feet msl must be equipped with an operable transponder and automatic pressure altitude reporting equipment. However, FAR 91.215(d)(1) and (2) allows the pilot to request ATC for a deviation from this requirement at any time.

Back to Top

ACCAR Relevance

Copyright©2003 Robert Patlovany


Summary:  The see-and-avoid principle was the only operational safety basis legally required for the pilot victims of the January 24 midair collision over Denver. Legally allowed head-on conflicts with closing speeds of greater than 400 knots, and with less than five seconds of pilot-visible time for detection and evasion, cannot be reliably handled by pilots using the see-and-avoid principle as long as the best-case out-the-window visual scan period takes over 20 seconds to complete. There was nothing in FAA regulations to prevent the Denver midair because the September 19, 1997, denial of a request for a Notice of Proposed Rulemaking (NPRM) No. 28996 due to "budgetary constraints" and failing to address an "immediate safety concern" [Ref. 1], ended FAA consideration of the Altimeter-Compass Cruising Altitude Rule (ACCAR)[Ref. 2]. The denied ACCAR proposal contained a valid safety basic for preventing the Denver midair collision. Since this denial, 147 easily avoidable deaths have resulted from ten midair collisions that could have been prevented with ACCAR at no cost to aircraft owners and pilots .

Discussion:   Federal Aviation Regulation (FAR) 91.113(b) places 100 percent of midair collision avoidance responsibility on all pilots in visual meteorological conditions (VMC), which prevailed over Denver during the twilight evening midair collision January 24, 2003. This responsibility assignment, formalized as a response to the San Diego, California midair collision September 25, 1978 and the Cerritos, California midair collision August 31, 1986, eliminated all Air Traffic Control (ATC) future responsibility for midair collisions in Visual Meteorological Conditions (VMC). This FAR was the primary reason why the pilots in the recent Denver midair collision were not required to be in radio contact with ATC personnel (even though they were) and ATC personnel were not required to provide collision alert warnings (even though they are allowed to do so under workload-permitting situations, as apparently happened less than three seconds before the moment of the Denver collision, per the final report text below). As a result there is no legal or administrative requirement that ATC personnel issue warnings to pilots soon enough that they may visually see a collision threat and avoid a midair collision. The conclusion that the pilots of the Piper were warned of head-on traffic less than three seconds before impact comes from the exerpt below from the final report. Notice that when the controller began to say traffic was a mile away at twelve o'clock, that traffic was actually about 0.2 miles away, and the impact probably occurred before the controller finished saying the warning. With a 340-knot (390-mph) closing speed, the warning began when the pilots were only 1.8 seconds away from impact. Most likely, the controller had not yet released the microphone key at the end of his warning when the aircraft had already collided.

At 1720:28, the controller asked the pilot of N360LL to report his altitude.
The pilot replied, "(Unintelligible) six." The controller said, "Say again."
At 1720:31, target separation had reduced to 0.29 miles. The pilot said, "Seven thousand, six hundred."
At 1720:33, the controller issued the pilot a traffic advisory: "Traffic is at twelve o'clock and a mile at seventy seven hundred, a Cessna." The pilot did not acknowledge this transmission.
At 1720:36, the two airplanes were 0.06 miles apart. Immediately thereafter, radar data indicated both targets had entered "coast" mode (i.e. computer-generated projection of targets' tracks and positions).

Remember that under the FARs, the pilots could have legally been in this collision geometry without ever talking to any controllers (even though they were both required to have Mode C altitude-encoding transponders, which wasn't obeyed in this case). In other words, nothing in the legal requirements was in force to prevent this collision over a highly populated area where six were injured and many homes were damaged or destroyed. The see-and-avoid principle was impossible to use to prevent this collision, or any other collisions at even higher legal closing velocities of up to 400 knots in this same airspace, as proven in Section 4.3 of "U.S. Aviation Regulations Increase Probability of Midair Collisions." The Altimeter-Compass Cruising Altitude Rule (ACCAR) could have been used to prevent the recent midair collision over Denver at any closing airspeed, even if the pilots never looked out the window. The ACCAR idea was developed over 70 years ago, and was promoted in four Air Facts articles during the 1960s [Ref 3]. The ACCAR idea was proven to be a far safer alternative to random altitude flight and to the hemispherical cruising altitude rule (FAR 91.159) in 1997 [Ref. 4]. An Air Traffic Control Quarterly article independently corroborated the fundamental findings supporting the safety basic of ACCAR in 2000 [Ref. 5].

The ACCAR idea requires that pilots spend as much time as possible, especially in high traffic areas, cruising level such that the actual magnetic heading of the aircraft matches the angle or "heading" of the 100-ft needle of the altimeter, as visualized by the pilot mentally superimposing a compass rose (or using a see-through sticker) on the altimeter cover glass. See the graphic depiction of ACCAR in Ref. 2. If all pilots cruise in this manner, all head-on midair collisions are automatically avoided by 500 feet of vertical clearance. The ACCAR idea costs aircraft owners and pilots nothing, because an operable magnetic compass and altimeter are already required by international minimum equipment regulations. Pilots need only about five minutes of thought and practice to master the ACCAR technique. Reference 4 proves that even if a pilot attempts ACCAR with large amounts of error, ACCAR flight safety is still significantly better than both random altitudes (like those of the descending Piper and climbing Cessna over Denver) and altitudes required by the hemispherical cruising altitude rules.

While ACCAR is a no-cost flight safety technique for aviators, its adoption does cost the FAA the embarrassment of having to acknowledge its failure since 1968 [Ref. 3] to incorporate the published state-of-the-art knowledge in its collision avoidance regulations and advisories. The FAA's "budgetary constraints" prevented a fair review of the request for NPRM 28996 in 1997, because ACCAR recommendations "do not address an immediate safety concern." The FAA rarely has an "immediate safety concern" with respect to midair collision safety, since its personnel are mostly safe on the ground. Consider the concern of the Piper Cheyenne and the Cessna 172 pilots in the January 24 Denver midair collision. They were legally flying head-on with a closing velocity of 340 knots, and about five seconds of time for the very best eyes in the very best weather to detect a midair collision threat. Legally, a head-on closing velocity of 500 knots is allowed by the FAA in Denver air space with no requirements for air traffic control intervention, and almost no hope of pilots visually detecting and evading such a midair collision.

The reason for this hopelessness is that visual acuity is only good enough for collision avoidance in about a 10-degree visual arc, as defined by the fovea, the most sensitive part of the human retinal. The FAA recommends that pilots visually scan each 10-degree sector near the horizon for at least one second. At best, it takes 18 seconds for a pilot to scan 180 degrees of forward airspace. For the five seconds that a fully legal 230 knot Piper Cheyenne and a 110 knot Cessna 172 might be visible to each other during a head-on approach, the probability for either pilot to detect the threat is 5/18, or 28 percent. (In contrast, for two seconds of visible time in each 10-degree forward sector, plus an instument panel scan of five seconds the detection probability is reduced to [5] / [[2][18] + 5] or 11 percent. See Secton 4.3 of Ref. 4). Simply summarized, at best there is a 72 percent probability that a Cheyenne-172 head-on collision will occur with neither pilot ever seeing the threat, even if they are focused primarily on their outside scan. (This simple calculation is mathematically strictly true only when one pilot is preoccupied with map reading, radio navigation, checklists, etc.--a frequent occurrence in any cockpit.) Remember, two aircraft may both legally fly at 200 knots directly at each other over Denver without talking to Air Traffic Control. Even with two pairs of eyes looking forwards at all times from each aircraft, a less than 3-second visible interval for a legal 400-knot head-on approach has almost no probability of being survived under the see-and-avoid principle. The ACCAR technique is a valuable tool denied to all pilots by political concerns for past liability over a long ago technical error to incorporate the physics of the mean free path formula in flight operation safety standards and regulations.

Back to Top


Source

NTSB Identification: MIA03FA124A/MIA03FA124B, Tuesday, June 17, 2003, Deerfield Beach, Florida
Aircraft: Cessna 182Q, registration: N759XA
Aircraft: Cessna 172N, registration: N4903F
Injuries: 5 Fatal

HISTORY OF FLIGHT

On June 17, 2003, about 1950 eastern daylight time, a Cessna 172N, N4903F, registered to and operated by Gulfstream Academy of Aeronautics, as a Title 14 CFR Part 91 personal flight, and a Cessna 182Q, N759XA, registered to and operated by Flying Double Eagle Inc., as a Title 14 CFR part 91 personal flight, collided while in cruise flight, about 300 yard east of the Deerfield Beach pier, Deerfield Beach, Florida. Visual meteorological conditions prevailed, and no flight plans were filed for either flight. Both airplanes were destroyed, and the private-rated pilot and two passengers on N4903F, as well as the commercial-rated pilot and one passenger on N759XA received fatal injuries. Both flights originated at Fort Lauderdale Executive Airport, Fort Lauderdale, Florida the same day. N4903F originated about 1835, and N759XA originated about 1940.

Witnesses stated that they saw both accident airplanes as they approached. They said that one airplane was proceeding from north to south, and the other airplane was proceeding from south to north. They stated that the southbound airplane was a little lower than the northbound airplane, and as they approached, a wing on the lower airplane was raised as if the pilot saw the other airplane at the last minute, and tried to turn, and the raised wing clipped a wing on the other airplane. According to the witnesses, the southbound airplane immediately descended in a spin/spiral, and impacted the water south of the Deerfield Beach pier at a near verticall angle, and the other airplane flew on a little longer, in what appeared to be a more controllable fashion, and impacted the water north of the pier.

Both airplanes impacted the surface, and settled on the bottom, in about 38 feet of water.

Back to Top

ACCAR Relevance

The hemispherical cruising altitude rules were not a factor in this midair collision. However, this collision most certainly could have been avoided by requiring ACCAR compliance at all altitudes. The technical error of believing that FARs 91.159 and 91.179 have some positive safety significance detracts from the proven necessity of replacing the risk multiplying hemispherical cruising altitude rule at any altitude with a far more universally effective linear cruising altitude rule, such as ACCAR. With ACCAR, these aircraft would have been automatically separated by 500 ft of vertical clearance. This accident shares a dangerous thread common found in witness reports from the Denver midair collision January 24, 2003, in that moments before impact, one plane was reported to suddenly bank, in a way that drastically increased the effective collision target absorption area. That is, two airplanes approaching head-on with perpendicular wings must be much further apart to avoid a collision than two aircraft with parallel wings. The Cessna 172 is 8.8 feet tall, and a Cessna 182 is 9.3 feet tall. If the two doomed aircraft had maintained a parallel-wings center-to-center vertical offset of (8.8 + 9.3)/2, or 9.1 feet, they would have passed each other without significant damage. However, if the lower southbound aircraft had a 172 wingspan of 36 feet and turned that wing perpendicular for collision avoidance, then the safe-passage center-to-center distance for vertical separation is increased to (9.3/2) + (36/2), or 22.7 feet. This ill-advised evasive maneuver is more than twice as likely to result in a midair collision as if simply maintaining the wings-parallel alignment, and using pitch control alone to increase the vertical margin of safety. This is the legacy of the hemispherical cruising altitude rule in ignoring the elementary physics of the mean free path formula as in the current regulations. Head-on collision paths are allowed (and even required) at common altitudes, and government advisories to pilots of geometric realities important to their safety are tragically inadequate.

This midair collision also contains similarities to the ones tabulated above for Burley, Vermilion, and Southern Gulf of Mexico. The usual cruising altitudes chosen by pilots in the crop dusting business are typically concentrated at the minimum safe altitude for clearing trees and power lines. This typically puts all such pilots in unnecessarily high-density airspace below 500 feet AGL. Similarly, coastal pilots wanting to avoid oil drilling platforms and highly populated beach areas tend to fly at about 1000 ft MSL or less, creating unnecessarily high density airspace at those altitudes. The ACCAR idea applied at all altitudes makes such naturally common, human-factors driven, risk-multiplying behavior illegal. In contrast, the current regulations REQUIRE risk-multiplying behavior at more that 3000 feet above the ground, while allowing unnecessarily and easily avoidable hazardous behavior closer to the ground.

Back to Top


Source

NTSB Identification: CHI03FA284A/CHI03FA284B, Friday, August 22, 2003 in Lake Elmo, MN
Aircraft: Aircraft: Cessna 172S: N53033
Aircraft: Piper PA-28-181: N38416
Injuries: 3 Fatal, 1 Serious.

HISTORY OF FLIGHT

The Cessna and Piper airplanes were destroyed when they impacted terrain after a mid-air collision. Both the Cessna and Piper aircraft were flying beneath the positively controlled Class B airspace of the Minneapolis-St. Paul International Airport. Both airplanes were operating under visual flight rules, and both airplanes were transmitting the 1200 VFR beacon code on their respective transponders. Neither airplane was required to be in radio contact with air traffic control. The student pilot in the Cessna who survived the accident reported that the CFI let him take the flight controls while they were flying straight and level. He reported that he was flying the airplane and was looking straight ahead, trying to maintain straight and level flight. He reported that the CFI put her hand on the throttle and started explaining a climb procedure. He reported that while the CFI was explaining the climb procedure, the airplane was hit by another airplane on the right side. He reported that he never saw the other airplane before the impact and that he didn't think the CFI saw it either. He reported that the CFI did not grab the controls or make any "violent maneuvers" prior to the impact. Radar data indicated that the Cessna departed Downtown St. Paul Airport (STP) at approximately 1719 to the northwest and turned right to an easterly heading, paralleling interstate highway I-94 to the east. The Cessna climbed to approximately 2,300-2,400 feet pressure altitude about 4 minutes after takeoff and remained at that altitude until impact, approximately 2 minutes later. The Cessna was traveling approximately 98 knots average ground speed during the 2 minutes prior to impact. The Piper departed South St. Paul Municipal Airport (SGS) at approximately 1719. Approximately 4 minutes after takeoff, the Piper turned to the northeast on a heading of about 027 degrees. The Piper climbed from about 1,900 feet pressure altitude to about 2,300 feet pressure altitude during the 2 minutes prior to impact. The relative bearing between the Piper and the Cessna was about 60 degrees. The radar data indicated the Piper was traveling at approximately 107 knots average ground speed during the 2 minutes prior to impact. Approximately 36 inches of the Cessna's outboard right wing structure was found lodged in the wing root of the Piper's left wing, and was located with the main wreckage of the Piper. The Piper's left wing exhibited a span-wise crease about five feet long in the lower wing skins forward of the flap. The Cessna's right wing leading edge had two distinct dents that were spaced a similar distance apart as the Piper's wing tie-down ring and jack pad. The aft left side of the Piper's fuselage in the vicinity of the registration number exhibited black, rubber-like transfer marks. The right tire from the Cessna's main landing gear had white scuff marks on the right side of the tire.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

Both pilots failed to maintain adequate visual lookout and did not maintain clearance from the other aircraft.

Full narrative excerpts:

The Cessna departed STP approximately 1719. Radar data indicated the Cessna departed to the northwest and turned right to an easterly heading. The radar track indicated that the Cessna was north of interstate highway I-94 and was paralleling the interstate to the east. The radar data indicated that the Cessna climbed to approximately 2,300-2,400 feet pressure altitude about 4 minutes after takeoff and remained at that altitude until impact approximately 2 minutes later. The radar data indicated the Cessna was traveling at approximately 98 knots average ground speed during the 2 minutes prior to impact.

The Piper departed SGS approximately 1719. Radar data indicated the Piper departed to the southwest and turned left to the east initially, and then turned to the north. Approximately 4 minutes after takeoff, the Piper turned to the northeast on a heading of about 027 degrees. The radar data indicated that between 1723:41 and 1725:32, the Piper climbed from about 1,900 feet pressure altitude to about 2,300 feet pressure altitude. During the 2 minutes prior to impact, the relative bearing between the Piper and the Cessna was about 60 degrees. The radar data indicated the Piper was traveling at approximately 107 knots average ground speed during the 2 minutes prior to impact.

Back to Top

ACCAR Relevance

The hemispherical cruising altitude rules were not a factor in this midair collision. However, this collision most certainly could have been avoided by requiring ACCAR compliance at all altitudes. With a 60 degree closing angle, these aircraft would have been cruising at altitudes 167 feet apart when their paths crossed.

Back to Top


Source

NTSB Identification: CHI04LA104A/CHI04LA104B, April 09, 2004, New Munster, WI
Aircraft: Cessna 172M, registration: N73213
Aircraft: Cessna 182S, registration: N355BD
Injuries: 2 Uninjured.

HISTORY OF FLIGHT

A Cessna 172M and a Cessna 182S both received substantial damage during a midair collision. Both airplanes landed without further incident. Visual meteorological conditions prevailed at the time of the accident. The pilot of the Cessna 172M stated that he was in level flight at 2,500 feet mean sea level when he felt and heard a thump from the rear of the airplane. After the collision, the pilot saw the Cessna 182S above, to the left, and in front of him. The pilot of the Cessna 182S stated that as he rolled out from a steep turn, he saw the Cessna 172M at his 2 o'clock position, slightly low and very close. A moment later, his landing gear struck the Cessna 172M's vertical stabilizer. Neither airplane was receiving air traffic control services. The pilot of the Cessna 182S stated that the purpose of his flight was flight proficiency with the intent to practice holding, procedure turns, and instrument approaches. The pilot of the Cessna 172M did not hold an airplane instrument rating and was receiving instruction prior to the accident flight toward an instrument ratting. The pilot of the Cessna 182S held an airplane instrument rating at the time of the accident. Neither pilot had a safety pilot aboard the accident flights.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows: Visual lookout not maintained by the pilots of both airplanes.

============full narrative excertps=============

On April 9, 2004, about 1918 central daylight time, a Cessna 172M, N73213, co-owned by the pilot, sustained substantial damage during a midair collision with a Cessna 182S, N355BD, operated by Waukegan Wings as a rental airplane, near New Munster, Wisconsin. N355BD sustained substantial damage. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flights were operating without flight plans and were not receiving air traffic control services. The private pilot of N73213 and the private rated rental pilot of N355BD were uninjured. N73213 originated from Palwaukee Municipal Airport, Wheeling, Illinois, at 1905, and N355BD originated from Waukegan Regional Airport (UGN), Waukegan, Illinois, at 1800. Both airplanes were en route to Burlington Municipal Airport (BUU), Burlington, Wisconsin.

Following the midair collision, N73213 landed at BUU and N355BD landed at UGN. Both airplanes landed without further incident.

The pilot of N73213 stated that he was en route to BUU on a heading of 340 degrees. The airplane's beacon, navigation, and taxi lights were on throughout the flight. He flew over Fox Lake and initiated a climb to about 3,000 feet mean sea level (MSL). About 15 miles from BUU, he descended to 2,500 feet MSL in order to intercept the BUU VOR and "perhaps" fly a visual BUU VOR 29 practice approach. About 9.4 miles south of BUU, while in straight and level flight, the pilot felt and heard a loud thump from the rear of his airplane. He did not see another airplane prior to the midair collision. Approximately 3 or 4 seconds after the collision, the pilot noticed another high-wing aircraft above, to the left, and in front of him. The other airplane was beginning to turn to a southbound heading.

The pilot of N355BD stated that he departed on a local proficiency flight and upon leaving UGN's airspace, he tuned to BUU's common traffic advisory frequency. About 1850, he departed from the BUU VOR at 2,500 feet MSL to an area south of Bong Air Force Base in order to avoid traffic at Westosha, Burlington, or Galt airports. About 1900, he made a clearing turn from 180 degrees to 90 degrees and the another clearing turn back to 180 degrees. The pilot stated that he did not see any air traffic during or after either clearing turn. He then performed a 45-degree steep turn to the right from 180 degrees and 2,500 feet MSL. After completing the turn, he retrimmed the airplane, and checked for traffic. He then made another 45-degree steep turn to the left at 2,440 feet MSL. He did not see any traffic while performing either turn.

He began his rollout to straight and level on a heading of about 200 degrees at 2,440 feet MSL. As he rolled out, he saw a Cessna Skyhawk at his 2 o'clock position, slightly low, on a heading of about 310 degrees, and very close. A moment later, his landing gear struck the Skyhawk's vertical stabilizer.

Back to Top

ACCAR Relevance

The hemispherical cruising altitude rules were not a direct factor in this midair collision. Both pilots were below 3000 AGL where 91.159 does not apply to VFR flight. However, both pilots were flying westerly and both were at a westerly formula altitude of 2500 ft MSL. Essentially they were both using the hemispherical formula altitudes were they are not required to do so. This artificially and unnecessarily increased their aircraft density at a formula altitude, while leaving nearby legal airspace unused for avoiding midair collisions.

This collision most certainly could have been avoided by requiring ACCAR compliance at all altitudes. ACCAR would have had the level cruising aircraft N73213 at about 2940 ft. The pilot of N355BD was maneuvering too frequently to be on any formula altitude. However, doing his maneuvering at essentially 2500 MSL placed himself at a common altitude to find other aircraft that are either flying the 91.159 formula (where not required in this case), or flying at a 500 ft altitude interval, as is a heuristically common practice amount pilots in general.

Back to Top


Source

NTSB Identification: SEA04FA083A/SEA04FA083B Sunday, May 16, 2004, Tenino, WA
Aircraft: Cessna 170B, registration: N3510D
Aircraft: : Cessna 210J, registration: N3329S
Injuries: 1 Fatal, 1 Minor

HISTORY OF FLIGHT

At 2038:10, a Cessna 170B and a Cessna 210J collided in-flight about 5 miles southeast of Tenino, Washington, at 3,000 feet mean sea level (about 2,700 feet above ground level). The Cessna 170B, flown by a private pilot, sole occupant of the airplane, was transponder equipped squawking code 1200 and emitting Mode C altitude information. The Cessna 170B had just descended from 7,500 feet msl and was leveling off at 3,000 feet on a magnetic heading of 322 degrees when the collision occurred. The pilot of the Cessna 170B, whose engine was separated from the airplane as a result of the collision, was able to maintain control of the airplane and succeeded in making a forced landing to an open field. The pilot of the Cessna 210J, also the sole occupant, was not emitting a transponder code, and therefore no altitude or other identifying information was available. However, a radar target was observed to the left and on a collision course with the Cessna 170B, and is assumed to have been the Cessna 210J; there were no other aircraft observed in the immediate vicinity. At 2036:11, the aircraft were approximately 3 1/2 nautical miles apart, the Cessna 210J oriented on a heading of north, while the Cessna 170B was on a magnetic heading of 309 degrees. At 2036:34, both aircraft were still on their respective headings, however, their lateral separation had diminished by 3/4 of a mile; the airplanes were now 2 3/4 miles apart. At 2036:58, lateral separation was reduced by 1/2 mile to 2 1/4 miles, and at 2037:22 lateral separation was further reduced to 1 1/4 miles. At 0337:46, 24 seconds prior to the collision, radar data indicates the aircraft were separated by a lateral distance of approximately 3,300 feet. Based on scratch marks and paint transfer signatures observed on both aircraft, as well as an estimated speed of the overtaking Cessna 210J being 150 knots and the GPS readout speed of the Cessna 170B of 113 knots, calculations revealed a closure speed of 41 knots, and a collision angle of 8 degrees. A calculated convergence angle of 22 degrees was determined for the Cessna 210J and 150 degrees for the Cessna 170B. It was concluded that based on the Cessna 210J's convergence angle and pilot's unobstructed forward field of vision, the Cessna 210J pilot should have been able to detect the presence of the Cessna 170B using normal visual scanning procedures consistent with visual flight rule (VFR) operations.

Back to Top

ACCAR Relevance

The hemispherical cruising altitude rules were not a direct factor in this midair collision. Both pilots were below 3000 AGL where 91.159 does not apply to VFR flight. However, both were at 3000 ft, which is an unnecessarily crowded cardinal altitude heuristically and systematically chosen by too many pilots. ACCAR would have prevented this accident. If the northerly pilot in the 210J had been at an ACCAR altitude of 3000 ft, and the 170B on a magnetic heading of 309 degrees had been at an ACCAR altitude of 2860 feet, they would have missed each other by more than 100 ft.

Back to Top



Source

NTSB Identification: NYC04FA185A/NYC04FA185B Saturday, August 07, 2004 in Kinnelon, NJ
Aircraft: Cessna A150L, registration: N6186F
Aircraft: Piper PA28-140, registration: N95314
Injuries: 2 Fatal

HISTORY OF FLIGHT

A Cessna A150L and a Piper PA28-140 collided during cruise flight while flying under day visual flight rules in visual meteorological conditions at approximately 0912:20. Radar data and data extracted from global position system receivers (GPS) found in each airplane were utilized to document the airplanes positions relative to each other. The Cessna departed from an airport (CDW) about 0905, climbed to a radar altitude of about 2,600 feet, and then flew a relatively steady northwest track until the time of the accident. The Piper departed to the south from another airport (N07), about 0909, entered a climbing right turn, and then flew a relatively steady track of 325 degrees. Initially, after the turn to the northwest, the Piper was flying ahead and below the Cessna. The Piper continued to climb on a track of 325 degrees to a maximum GPS altitude of 2,680 feet, while being overtaken by the Cessna. Both airplanes collided while in straight and level flight.

A visibility study was conducted using the GPS position data recovered. According to the study the airplane visibility charts the pilot of the Cessna had an approximate 21 second opportunity to acquire the Piper had he been scanning down and to his right, while cruising at 2,600 feet. The Piper at this time was climbing on a southerly track from 375 to 700 feet. The pilot of the Piper had a 21 second opportunity to acquire the Cessna, if he had been scanning forward and to his left while climbing out from 725 to 975 feet and turning from a course of 190 to 250 degrees, on departure to the west. The Cessna at this time was traveling to the northwest, and level at 2,600 feet. The two airplanes continued to converge until they collided and departed from controlled flight, respectively. The airplanes were not in a position for the respective pilots to see each other during the two and a half minutes that preceded the accident. The airplanes impacted the ground about 750 feet apart, in two distinct wreckage fields.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

Both pilots inadequate visual lookout, which resulted in a midair collision.

Excerpts from full narrative

The radar and GPS data was utilized to determine the ground track and ground speed for each airplane, as well as the closure rate, relative azimuth and relative elevation between the two airplanes. A number of assumptions were required before the data could be utilized to determine if and when the pilot of one airplane could see the other, and where in the pilot's windscreen the other airplane would have appeared.

Airplane visibility charts created for the accident indicated that the pilot of the Cessna had an approximately 21-second opportunity to acquire the Piper, had he been scanning down and to his right, while cruising at 2,600 feet, and heading to the northwest. The Piper at this time was climbing on a southerly track from 375 to 700 feet. The pilot of the Piper had a 21 second opportunity to acquire the Cessna, if he had been scanning forward and to his left while climbing out from 725 to 975 feet, and turning from a course of 190 to 250 degrees, on departure to the west. The Cessna at this time was traveling to the northwest, and level at 2,600 feet. The two airplanes continued to converge until 0912:20, at which time the closure rate began to vary dramatically, consistent with a departure from controlled flight for at least one of the airplanes.

During this period, airplane airspeed dropped slightly, and aircraft bearing changed significantly, for both airplanes, from the constant steady state values they had been maintaining just prior to the upset. Data from the Cessna's GPS indicated that the airplane's groundspeed dropped from 94 mph to 39 mph and bearing changed from 330 to 313 degrees within this timeframe. Data from the Piper's GPS indicated that the airplane's groundspeed changed from 87 mph to 49 mph, and bearing changed from 325 to 298 degrees also within this timeframe. The calculations also showed that at no time after 0909:57, up until the time of collision, at 0912:20, could the pilot of either airplane see the other.

Back to Top

ACCAR Relevance

The hemispherical cruising altitude rules were not a direct factor in this midair collision. Both pilots were below 3000 AGL where 91.159 does not apply to VFR flight. However, both were cruising at 2600 ft, which is only 100 ft above a VFR hemispherical formula altitude for westerly aircraft. Under ACCAR, the Piper on a heading of 325 degrees would have been at an altitude of 2902 ft, while the Cessna heading 330 would have been at an altitude of 2916, providing 14 feet of centerline clearance. Accurately flown, ACCAR would have prevented this collision.

Keep in mind that with only a 5-degree heading difference and a 7-mph velocity difference, these aircraft were in effect flying in a gradually tightening formation in close proximity for a fairly long time before impact. The faster Cessna would have approached slowly from slightly aft and slightly behind the wing of the slower Piper. The closing speed would have been about 16 mph. A wing strut or window frame could have hidden a threat for a long time. Discounting structural blind spots, these pilots were close enough to see each other for several minutes before impact.

Notice that the NTSB report says each pilot had 21 seconds to visually acquire the other pilot at a previous time, but not during the 2.5 minutes immediately before impact. If this NTSB conclusion disavows the effectiveness of the see-and-avoid principle in the final moments before impact, then only ACCAR could have prevented this collision. The Risk Analysis article notes that if the visible time before impact is greater than the length of time of the pilots' the visual scan cycle, then it is physically impossible to guarantee that visual detection will occur. Scanning the forward 180 degrees in ten, 10-degree-angular, one-second-time increments (the maximum-angle, minimum-time intervals recommended by the FAA) takes 18 seconds. Adding the normal instrument panel scan period would have exceeded the 21 seconds available for the most visually diligent pilots to have detected each other in this collision. While ACCAR would have provided only about 14 feet of path separation, the see-and-avoid technique was declared unusable by the NTSB during the final 2.5 minutes before impact. Therefore, the cause judgment, "Both pilots inadequate visual lookout, which resulted in a midair collision," was at best unfair and not useful for preventing future collisions.


Source

NTSB Identification: LAX04FA301A/LAX04FA301B Sunday, August 22, 2004 in Malibu, CA
Aircraft: Bellanca 7ECA, registration: N53879
Pollard & Huntley Thorp T-18, registration: N7618T
Injuries: 3 Fatal

HISTORY OF FLIGHT

A Bellanca 7ECA Citabria and an experimental Thorp T-18 collided in flight during separate local area flights along the southern California shoreline. Both airplanes impacted the ocean in the area of the collision. Day visual meteorological conditions prevailed, with no visibility restrictions. Review of the recorded radar data showed the Citabria as a primary target with no mode C altitude reporting. The Thorp was identified as a secondary 1200 VFR beacon code with mode C altitude reporting. The Citabria's target radar track showed it flying south over the coastal hills until it intersected with the shoreline. At the shoreline, the Citabria's target passed in front of the Thorp's radar target and continued southbound until it was about 0.75 nautical miles (nm) offshore. The Citabria's radar target then turned left 180 degrees, heading back toward the north. The Thorp target flew along the coastline until about 8 nm northwest of the accident site. The target made a right 180-degree turn, and started to track back along the coastline. About 2 nm northwest of the collision point, the target's mode C reported an altitude of 2,400 feet msl. The target's mode C altitude radar return continued to increase in altitude until the radar track stopped. At this time, the separation between the two targets was about 0.5 nm. The radar track shows the Thorp's target continued eastbound along the coast in a slight climb, and the Citabria's target continued northbound until radar contact with the Thorp was lost at 1729:37, at an altitude of 2,900 feet msl. The radar target on the Citabria was lost at 1730:10. The radar tracks of both aircraft were approximately perpendicular in the last minutes of flight. Both aircraft impacted the water after the midair collision. The Citabria washed ashore on the beach. The Thorp impacted the water about 150 yards east of the Citabria and sank in about 20 feet of water. Both airplanes were destroyed during the collision and impact sequence with the water, and further damaged by tidal action prior to and during the recovery process. All flight control components and control surfaces for the Citabria were accounted for in the recovered wreckage. The left wing strut, which was white in color, was missing and not recovered from the ocean. An examination of the Citabria wreckage for paint transfer marks from the Thorp met with negative results. Examination of the Thorp was inhibited due to the damage to the airplane wreckage by the post accident impact with the ocean and the subsequent tidal action prior to and during the recovery process. The examination of the propeller revealed white in color paint transfers marks beginning close to the hub and extending outward toward the tip. At the tip of one of the blades there was a large gouge on the leading edge. An examination of the Thorp wreckage for paint transfer marks revealed a series of light blue paint transfers on the underside of the right horizontal stabilizer cap. The light blue paint was similar to the coloration of the Citabria. Both airplanes were operating in uncontrolled class 'G' airspace when the collision occurred. The National Transportation Safety Board determines the probable cause(s) of this accident as follows: The failure of both pilots to maintain an adequate visual lookout and their failure to see and avoid the other airplane. Full narrative excerpts: The first identified radar target for the Citabria was about 15 nautical miles (nm) north of the collision point. The Citabria radar target was a primary radar return. No altitude information was available from the radar data. The Citabria target's radar track showed it flying south on the west side of Highway 23 until it intersected with the Pacific Coast Highway. At the shoreline, the Citabria's target passed in front of the Thorp's radar target and continued southbound until it was about 0.75 nm offshore. The Citabria's radar target then turned left 180 degrees, heading back toward the north. The Thorp departed Torrance about 1700, and review of recorded radar data showed a secondary 1200 (VFR) beacon code at a mode C reported altitude of 400 feet mean sea level (msl). The target flew along the coastline until about 8 nm northwest of the accident site. The target made a right 180-degree turn, and started to track back along the coastline. About 2 nm northwest of the collision point, the target's mode C reported an altitude of 2,400 feet msl. The target's mode C altitude radar return continued to increase in altitude until the radar track stopped. The last radar return on the target was at 1729:37, at an altitude of 2,900 feet msl. At this time, the separation between the two targets was about 0.5 nm. The radar track shows the Thorp's target continued eastbound along the coast in a slight climb, and the Citabria's target continued northbound until radar contact with the Thorp was lost at 1729:37 at an altitude of 2,900 feet msl. The radar target on the Citabria was lost at 1730:10.

Back to Top

ACCAR Relevance

The hemispherical cruising altitude rules were not a factor in this midair collision. Both pilots were below 3000 AGL where 91.159 does not apply to VFR flight. Unfortunately, geographic features artificially produce high concentrations of aircraft. Scenic coastlines, rivers, highways, etc., provide attractive locations to fly. These aircraft collided from a 90-degree angle. The ACCAR formula would have provided about 250 feet of vertical separation, if it were used by all cruising aircraft at all altitudes.

Back to Top


Source

NTSB Identification: CHI05FA055A/CHI05FA055B, Tuesday, January 18, 2005 in Hollister, OK
Aircraft: Cessna T-37B: 66-8003
Air Tractor AT-502B: N8526M
Injuries: 1 Fatal, 1 Minor, 1 Uninjured

HISTORY OF FLIGHT

On January 18, 2005, approximately 1128 central standard time, a Cessna T-37B, a twin-turbojet military trainer, tail number 66-8003, operating under the call sign Cider 21, and an Air Tractor AT-502B single-engine agricultural airplane, N8526M, were destroyed following a midair collision during cruise flight near Hollister, Oklahoma. The T-37B was registered to and operated by the United States Air Force (USAF). The AT-502B was registered to a private individual and operated by a commercial pilot. The USAF flight instructor pilot was not injured and the USAF student pilot sustained minor injuries. The commercial pilot in the AT-502B was fatally injured. Visual meteorological conditions prevailed and the airplanes were operating in Class E airspace. The T-37B was in radar contact with approach control and was operating under Air Force Instructions (AFI) 11-202, Volume III. The AT-502B was operating under 14 Code of Federal Regulations Part 91 for the delivery flight, and a flight plan was not filed. The local flight for the T-37B originated from the Sheppard Air Force Base (SPS), near Wichita Falls, Texas, approximately 1022. The cross-country flight for the AT-502B originated from the Olney Municipal Airport, near Olney, Texas, approximately 1100, and was destined for Huron, South Dakota, with an intermediate fuel stop in Hutchinson, Kansas.

Full narrative excerpts

On January 18, 2005, approximately 1128 central standard time, an Air Tractor AT-502B single-engine agricultural airplane, N8526M, and a Cessna T-37B, a twin-turbojet military trainer, tail number 66-8003, operating under the call sign Cider 21, were destroyed following a midair collision during cruise flight near Hollister, Oklahoma. The AT-502B was registered to a private individual and operated by a commercial pilot. The T-37B was registered to and operated by the United States Air Force (USAF). The commercial pilot in the AT-502B was fatally injured. The USAF flight instructor pilot was not injured and the USAF student pilot sustained minor injuries. Visual meteorological conditions prevailed and the airplanes were operating in Class E airspace. The AT-502B was operating under 14 Code of Federal Regulations Part 91 for the delivery flight, and a flight plan was not filed. The T-37B was in radar contact with approach control and was operating under Air Force Instructions (AFI) 11-202, Volume III. The cross-country flight for the AT-502B originated from the Olney Municipal Airport, near Olney, Texas, approximately 1100, and was destined for Huron, South Dakota, with an intermediate fuel stop in Hutchinson, Kansas. The local flight for the T-37B originated from the Sheppard Air Force Base (SPS), near Wichita Falls, Texas, approximately 1022.

According to company personnel from an Air Tractor dealership in Arkansas, the pilot was hired to deliver the recently purchased AT-502B to the new owner in Huron, South Dakota. Company personnel at the Air Tractor factory located in Olney, Texas, reported that the AT-502B was equipped with basic visual flight rules (VFR) instruments and was not equipped with any radios or a transponder.

During an interview with the NTSB investigator-in-charge (IIC), the USAF flight instructor and student pilot reported that they were on a routine mission training flight (C2803). After a non-eventful departure from SPS, they performed two normal overhead approaches to SPS before being cleared into the Military Operations Area (MOA). After completing the series of high altitude maneuvers, the training flight received radar vectors to the RANCH intersection and then to the Frederick Municipal Airport (FDR), near Frederick, Oklahoma, which is commonly referred to by the USAF as "Hacker." As the flight descended to an altitude of 6,000 feet, the instructor noted the bottom of the overcast cloud ceiling to be between 6,000 and 6,500 feet mean sea level (msl).

After arriving at Hacker, the training flight performed a straight in no flap landing, and requested left closed traffic for practice landings. After completing a normal overhead approach and a single-engine landing, the flight proceeded to depart Hacker's airspace to the east and climbed to 5,500 feet msl.

The student pilot reported that he performed the en route portion of his checklist and contacted USAF Radar Approach Control (RAPCON) to notify them they were en route back to Sheppard Air Force Base and requested the "home plate" arrival. RAPCON advised the flight that they had radar contact, and to descend to 5,000 feet msl on a heading of 100 degrees.

The student pilot reported that after he leveled off at 5,000 feet msl at an indicated airspeed of 200 knots, the flight instructor took control of the T-37B. The student pilot stated that as the flight instructor took control of the aircraft, he scanned outside the airplane to the left, and started to look back to the right when he saw the yellow Air Tractor heading toward the right side of the T-37B. He reported, "… I saw the crop duster and it was just an immediate … it wasn't like I saw him moving, it's just like it grew and my jaw just dropped and I didn't say anything. I was just … I just said, "Sir," because I was just shocked and as soon as I said that, we just impacted and went out of control."

The instructor pilot stated that he took control of the airplane while still in the descent and he leveled the airplane at 5,000 feet msl. He reported that he briefly scanned at the student pilot's altimeter on the left side of the instrument panel (a standard practice for T-37 flight instructors). As he was turning his head back to the right, he noticed a "high visibility yellow airplane" out of the right corner of his eye, but did not have time to take evasive action.

Both pilots reported that the T-37B was level at 5,000 feet msl for about one minute or less before impact with the AT-502B. The instructor and student pilot recalled feeling a spinning sensation and rolling inverted. Both the instructor and student pilot initiated emergency egress procedures and ejected from the aircraft. The T-37B and AT-502B impacted farm fields about 3.5 nautical miles (nm) east of Hollister, Oklahoma.

AIRCRAFT INFORMATION

The Air Tractor AT-502B, serial number 502B-2570, was a low wing, tailwheel equipped, steel tubular frame design airplane with a fixed landing gear. The AT-502B was not equipped with a radio or a transponder. The Air Tractor factory representative reported that radios and transponders are typically not installed on new aircraft at the factory. He reported that new owners prefer to have the equipment installed on the airplanes with the entire avionics package that are typically purchased from an avionics shop selected by the new owner. Airplanes are not required to be equipped with a radio or transponder as long as FAR 91.215 "ATC transponder and altitude reporting equipment and use" is not violated.

AIRPORT INFORMATION

The normal controller actions following a T-37 call up off of Hacker en route to SPS are stated below:

"Once the Sheppard Arrival controller radar identifies the T-37 requesting to return to Sheppard AFB, the controller issues an altitude to maintain and easterly heading. The actual altitude and heading depend on other traffic, the runway in use, and the entry point or approach requested by the pilot. The typical altitude is 5000 feet. The controller sequences the T-37 with other traffic inbound to Sheppard AFB and separates the aircraft from other IFR aircraft. (Note: no separation is required from other VFR aircraft.) While en route to Sheppard AFB, aircraft will receive traffic advisories on any known or observed conflicting traffic based on controller workload and equipment limitations."

The procedures for handling non-squawking VFR aircraft transiting Sheppard airspace are stated below:

"Procedures for handling non-squawking VFR aircraft transiting Sheppard airspace are governed by FAA Order 7110.65. Traffic advisories are issued to aircraft Sheppard ATC is controlling based on controller workload and equipment limitations. If a controller determines that an aircraft on his/her frequency will be in conflict with any other known or observed traffic, the aircraft on the controller's frequency will receive a traffic advisory (workload permitting)."

TESTS AND RESEARCH

Radar Study

The "valid" AWACS code 4221 altitude data for the period approaching the accident indicated that the altitude of Cider 21 at 11:27:24 and 11:27:55 was about 5,500 feet MSL. At 11:28:05, the altitude was about 4,970 feet MSL. Examination of FAA and AWACS data showed no primary targets in the area of the accident site during the period of interest.

The RAPCON transcript indicated that at 11:27:50, the RAPCON controller, SPS-37AA, stated the following, "JAVIT27 Point Out approved. Traffic, CD21, 5,000, eastbound." At 11:27:57, the SPS-S2AA controller stated, "Cider 21, traffic observed." During interviews, the RAPCON controllers stated that they observed Cider 21 depicted on their radarscopes at 5,000 feet about 4nm south of Ranch, a VFR entry point for Hacker. The controllers reported that they did not observe any non-squawking primary targets displayed on their radarscopes in the airspace near the accident site.

USAF Aerospace Physiology Study

A USAF Aerospace Physiologist performed a study to determine the cockpit blind spots for each pilot based on relevant cockpit obstructions, and to determine the pilot visual acquisition/reaction time data. Based on distances and angles obtained by in-cockpit measurements, average human morphology, and measured eye to obstruction distances in normal flying positions, the following results were obtained:

The pilot's blind spot from the AT-502B left roll cage/door structure produced an eye position to obstruction angle of 49 degrees to the front edge, 56 degrees to the center, and 63 degrees to the aft edge, respectively.

The USAF instructor pilot's blind spot from the T-37B's right canopy bow produced an eye position to obstruction angle of 48 degrees to the front edge, 54 degrees to the center, and 61 degrees to the aft edge, respectively.

The USAF student pilot's blind spot from the T-37B's right canopy bow produced an eye position to obstruction angle of 73 degrees to the center (edge measurements not feasible due to cross-cockpit distances).

The total pilot reaction time was determined to be 3.7 seconds. The reaction time data is listed as follows:

Latent Reaction Time: 0.4 seconds

Stimulate retinal receptors: 0.1 second

Set up & move eye: 0.2 seconds

Foveal perception: 0.1 seconds

Recognition (0.65 - 1.5 seconds): 0.8 seconds

Decision Time (1 - 3 seconds): 2.0 seconds

Sub-total: 3.2 seconds

Movement Time: 0.5 seconds

Motor impulse: 0.1 seconds

Gross movement: 0.4 seconds

Total Reaction Time: 3.7 seconds

Based on pilot interviews and wreckage examination, the impact angle of the two airplanes was determined to be about 100 degrees. The USAF Aerospace Physiologist determined that the AT-502B's left roll cage/door structure created a blind spot that occluded the T-37B from the AT-502B's pilot's line of sight during the last 30 seconds prior to impact. He determined that the T-37B's right canopy bow did not produce a blind spot for the T-37B pilots, and that the AT-502B was not occluded during the last 30 seconds prior to impact.

ADDITIONAL INFORMATION

The distance between ONY and the impact site was about 60nm. The direct course between ONY and the impact site was 001 degrees true. The magnetic course was about 354 degrees magnetic. Due to the unavailability of recorded radar data, the actual magnetic course and the altitudes flown by the pilot of the AT-502B is unknown.

The VFR cruising altitudes are prescribed in FAR 91.159. The VFR cruising altitudes for level cruising flight for 3,000 feet above the surface and below 18,000 feet MSL are as follows:

(1) On a magnetic course of zero degrees through 179 degrees, any odd thousand foot MSL altitude +500 feet (such as 3,500, 5,500, or 7,500); or

(2) On a magnetic course of 180 degrees through 359 degrees, any even thousand foot MSL altitude +500 feet (such as 4,500, 6,500, or 8,500).

The airspace at the accident location is designated as Class E airspace. Class E airspace is defined by the Aeronautical Information Manual (AIM) as: "generally, if the airspace is not Class A, Class B, Class D, and it is controlled airspace, it is Class E airspace. No specific pilot certification or specific aircraft equipment is required to fly in Class E airspace. No separation services are provided to VFR aircraft operating in Class E airspace.

The Right-of-way rules for converging aircraft are prescribed in FAR 91.113 (d). The regulation states the following:

(d) Converging. When aircraft of the same category are converging at approximately the same altitude (except head-on, or nearly so), the aircraft to the other's right has the right-of-way.

Back to Top

ACCAR Relevance

These two aircraft collided at 5000 ft MSL in VMC conditions. The jet was near the end of its cruise phase preparing to transition to a standard VFR approach typically starting at 5000 ft MSL for this airport.

"The direct course between ONY and the impact site was 001 degrees true. The magnetic course was about 354 degrees magnetic. Due to the unavailability of recorded radar data, the actual magnetic course and the altitudes flown by the pilot of the Air Tractor AT-502B is unknown." This quotation reflects the inherent ambiguity of FARs 91.159 and 91.179 near polar headings. Obviously, a heading of 359 degrees cannot possibly be just as safe at 4500 MSL, as the level of safety using a heading of 001 degrees at 5500 MSL, as required by the FARs. In any case for VMC, the Air Tractor following 91.159 should have been at 4500 or 5500, and the eastbound jet should have been at 5500 ft. "Based on pilot interviews and wreckage examination, the impact angle of the two airplanes was determined to be about 100 degrees." In this accident, the heuristic tendency to fly at cardinal altitudes (in this case, 5000 MSL) combined with the jets expected typical approach altitude of 5000 MSL combined to put both aircraft at an artificially unnecessarily high density common altitude. If they had both been obeying 91.159, there is a 50/50 chance that the ambiguously regulated northbound Air Tractor would have been at the same 5500 MSL altitude required for easterly aircraft. In contrast, if both aircraft were flying level at ACCAR formula altitudes, then the 100 degree intercept would have separated their flight paths by 278 feet of vertical clearance.

Notice also the level of detail in the report establishing the Total Reaction Time as 3.7 seconds. Notice the conclusion that the Air Tractor pilot's vision was blocked by structure during the last 30 seconds to impact, while the jet pilots' vision was not blocked in the last 30 seconds. This implies that the jet pilots were more at fault for failing to notice the Air Tractor during the final visible 30 seconds, while the Air Tractor pilot was less at fault because the Air Tractor's structure blocked the approaching threat angle of the jet from his vision during that same 30 seconds. However, a 200-knot jet closing on a 100 knot aircraft at a 100 degree angle probably won't be visible for 30 seconds. A ten-second visibility would be the most one could expect for that closing situation. This time is far shorter than the fastest possible 180 degree outside plus inside panel scan cycle of about 20 seconds, leaving about a 50% probability that one pilot could even detect the approaching threat during the 10 seconds of useful visibility. Considering the 3.7-second reaction time considered with the 10 second visible time, the see-and-avoid principal simply could not possibly be reliable for guaranteeing the safety of this path crossing geometry.

Back to Top


Source

NTSB Identification: DFW05LA182A/DFW05LA182B, Thursday, July 14, 2005 in Bonita, LA
Aircraft: Ayres S2R-T34: N61220
Ayres S2R-T15: N3098R
Injuries: 2 Uninjured

HISTORY OF FLIGHT

Two single-engine agricultural airplanes collided in flight while maneuvering. Both airplanes were of the same make, but different model and were both operated by the same operator. One aircraft, being flown by a 16,000 hour pilot, had just completed an aerial application mission and initiated a high rate of climb on a westerly heading. The second aircraft, which was being flown by a 10,337-hour pilot, was in cruise flight at 500 feet above the ground, returning to a private grass airstrip on a northerly heading. The propeller of the climbing airplane struck the right wing of the airplane in cruise flight. The pilot of the airplane in cruise banked the airplane to the left and initiated a descent to avoid the climbing airplane. The pilot of the airplane in cruise flight landed without further incident at a nearby grass airstrip, while the pilot of the climbing airplane elected to make a forced landing to a cotton field. The airplane was damaged during the forced landing. The airplanes were not in radio contact with each other at the time of the accident. The operator reported that both pilots had been on duty for at least 8 hours at the time of the collision.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows: The failure of the pilot to maintain an adequate visual lookout, which resulted in a midair collision. A contributing factor was the unsuitable terrain for a forced landing.

Full narrative exerpts

DFW05LA182A

On July 14, 2005, approximately 1630 central daylight time, a single-engine Ayres S2R-T34 agricultural airplane, N61220, and a single-engine Ayres S2R-T15 agricultural airplane, N3098R, collided in-flight while maneuvering near Bonita, Louisiana. N61220 sustained substantial damage and N3098R sustained minor damage. The two commercial rated pilots were not injured. Both aircraft were registered to and operated by McGinty Flying Service of Jones, Louisiana. Visual meteorological conditions prevailed, and flight plans were not filed for either flight. Both airplanes were operating under 14 Code of Federal Regulations Part 137 aerial application flight. N61220 originated from a private grass airstrip near Jones, Louisiana, and N3098R originated from a private grass airstrip near Bonita, Louisiana, approximately 1500.

The 16,000-hour pilot of N61220 reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that he had just completed spraying a plowed cotton field and was on an westerly heading, when he pulled the airplane to a nose high attitude of approximately 45 degrees. Upon climb out, the airplane's propeller struck the right wing of N3098R, which was crossing overhead on a northerly heading. In a subsequent telephone interview with an NTSB Investigator, the pilot stated that after the collision he, "felt the aircraft begin to vibrate" and decided to reduce power and make a forced landing to a nearby plowed cotton field. During the landing roll, the airplane struck a crop row which resulted in damage to the propeller, main landing gear and firewall.

The 10,337-hour pilot of N3098R reported in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) that the airplane was on a northerly heading at approximately 500 feet above ground level when he caught a glimpse of an airplane climbing towards him off of his right wing. The pilot then banked the airplane to the left and began to descend to try to avoid a collision. The propeller of N61220 struck the right wing of N3098R severing the aft wing spar extension. The pilot then landed without incident at a private grass airstrip near Bonita, Louisiana.

The airplanes were not in radio contact with each other at the time of the accident. The operator reported that both pilots had been on duty for over 8 hours at the time of the accident.

At 1553, the automated surface observing system (ASOS) at the Monroe Regional Airport, near Monroe, Louisiana, located approximately 28 nautical miles southwest of the accident reported wind from 170 degrees at 12 knots gusting to 16 knots, visibility 10 statute miles, few clouds at 3,800 feet, temperature 89 degrees Fahrenheit, dew point 75 degrees Fahrenheit, and a barometric pressure of 29.89 inches of Mercury.

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate the unnecessarily high aircraft density that results when pilots follow tendencies to fly at altitudes that artificially and unnecessarily increase aircraft collision threat concentrations. Many aerial application pilots routinely cruise just barely above the trees and power lines with minimal terrain clearance. If every pilot did this, the midair collision model would almost resemble high-speed boats on a lake, where any ground path coincidence would be at the same altitude. This accident shares many similarities with the aerial applicator accidents June 02, 2001, in Anguilla, MS, and July 16, 1998, in Burley, Idaho.

If ACCAR was applied in this scenario, the southbound cruising Cessna would have been at altitudes such as 1500, 2500, etc., and the Robinson headed southwest would have been at altitudes such as 1625, 2625, etc. Using ACCAR, the two flight paths would have been about 125 feet apart.

Notice that one pilot "caught a glimpse of an airplane climbing towards him off of his right wing. The pilot then banked the airplane to the left and began to descend to try to avoid a collision. The propeller of N61220 struck the right wing of N3098R severing the aft wing spar extension." This midair collision would not have been a collision if the pilot had not banked, thereby maximizing the vulnerable collision cross sectional area of his aircraft. The left bank exposed the right wing to damage that would not have occurred if the wing had been left pointed directly at the incoming collision threat. This conclusion is supported by the fact that no part of his fuselage was damaged in the collision. Having left the wing and fuselage in the same geometric plane pointed at the collision threat would have resulted in the wing and fuselage having survived unscathed together. A better collision avoidance maneuver would have been to keep the wings pointed at the threat, and just pitched down to increase the distance between the flight paths of the two aircraft.

Back to Top


Source

NTSB Identification: NYC06FA025A/NYC06FA025B, Saturday, November 05, 2005 in Pohatcong, NJ
Aircraft: Cessna 172A: N7467T
Joseph E. Crosby Zodiac CH 601HDS: N6384E
Injuries: 1 Fatal, 1 Minor HISTORY OF FLIGHT

On November 5, 2005, about 1138 eastern standard time, a Cessna 172A, N7467T, an amateur built Zodiac CH 601HDS, N6384E, were substantially damaged during a midair collision over Pohatcong, New Jersey. The certificated Private pilot flying the Zodiac, which departed Alexandria Airport (N85), Pittstown, New Jersey, was fatally injured, and the certificated private pilot flying the 172A, which departed from Van Sant Airport (9N1), Erwinna, Pennsylvania, received minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for either local flight, conducted under 14 CFR Part 91.

Witnesses stated, that both airplanes appeared to converge with each other above the Phillipsburg, New Jersey exit, on Interstate 78. Multiple "white" objects described by a witness as "leaflets" were also observed to fall from the airplanes and a large "bang" was reported.

According to the pilot of the Cessna, he was in cruise flight indicating approximately 90 mph at 1,800 feet above mean sea level over Alpha, New Jersey, heading northwest towards the Delaware River. He heard and felt "a tremendous crash" and observed a "flash of blue" out the windscreen at his 2 o'clock position. After regaining control of the airplane he was unsure of damage that may have occurred and immediately began looking for a place to land. After performing two 360-degree turns to locate a suitable emergency landing area he observed a cornfield that appeared to be of sufficient length, 1/4 mile to the northwest of the Phillipsburg exit, and executed a successful landing.

The Cessna came to rest on a magnetic heading of 316 degrees. Examination of the airplane revealed damage to the upper left portion of the cowling. Impact damage to the #6 cylinder was visible and the engine appeared to have been displaced laterally to the right. The propeller exhibited multiple chordwise scratches to the blade face near the tips along with surface scuffing along the length of the blades. Further examination revealed crush damage and buckling of the lower right cowling and paint transfer marks on the surface of the crushed area.

The left wing remained partially attached to the main wreckage by portions of the spar cap. The leading edge was separated forward of the spar, at the upper wing skin attach rivet line for about 3/4 of the span of the wing and the left fuel tank was breached. Flight control continuity was confirmed from the left aileron to the wing root area.

The fuselage area had come to rest partially inverted and was orientated on a magnetic heading of 276 degrees. The debris field was 20 feet in length. Portions of the canopy were missing. Crush damage was visible at the right wing root, upper portion of the aft fuselage, and cockpit. The firewall exhibited impact damage and the instrument panel was separated from the majority of its mounts and had been displaced into the right seat area. Approximately 4 feet of the right wing spar, stripped of its surrounding structure was found partially attached to the right wing root.

Both the horizontal stabilizer, elevator and rudder were found separated from their mounts 5 feet 9 inches aft of the fuselage, resting against the base of a tree. Control continuity was established to the rudder, and rudder control pedals.

Portions of the right wing, right fuel tank, right spar assembly, and wing skin were recovered from various locations along Interstate 78 and the surrounding area.

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate a missed opportunity for a collision that could have been avoided with ACCAR.

Each aircraft was cruising generally northwest after taking off about 10 miles from each other and intersecting after flying about 15 miles. Their departure airports were at elevations 390 and 480 ft MSL. The surviving pilot noted cruising at 1800 MSL at the time of collision. Based on departure airport elevations and the relatively short cruise length to the accident site, both pilots were approximately 1000 ft AGL over the high points in the local terrain. The closing angle based on the departure airport locations and the accident location was about 30 degrees. If both pilots had been using ACCAR, their paths would have crossed with about 80 feet of vertical clearance. If too may pilots cruise at the lowest safe altitude for terrain clearance, they will be flying in artificially high collision target concentrations. ACCAR systematically separates pilots who might otherwise congregate at similar altitudes.

Back to Top


Source

NTSB Identification: LAX06FA106A/LAX06FA106B, Wednesday, February 08, 2006 in El Cajon, CA
Cessna 172RG: N9531B
Cessna 182Q: N759KE
Injuries: 3 Fatal

HISTORY OF FLIGHT

On February 8, 2006, at 1642 Pacific standard time, a Cessna 172RG, N9531B, and a Cessna 182Q, N759KE, collided in flight approximately 3 miles south of the Gillespie Field Airport (SEE), El Cajon, California. Both aircraft were destroyed in the collision sequence and post impact fires. The certified flight instructor and pilot undergoing instruction in the Cessna 172RG and the private pilot, the sole occupant, in the Cessna 182Q, were fatally injured. The Cessna 172RG departed from Gillespie Field, at 1637 on a tower en route instrument flight rules clearance and was destined for Brown Field Municipal Airport (SDM), San Diego, California, an airport 15 miles south of Gillespie Field. The Cessna 182Q departed Gillespie Field at 1638 on a local visual flight rules flight to the Brown Field airport. Visual meteorological conditions prevailed, with a visibility of 25 miles.

Preliminary information supplied by the Federal Aviation Administration indicates that the Cessna 172RG was issued a takeoff clearance at 1638, and was subsequently handed off to the Southern California Terminal Radar Approach Control (TRACON) facility. The Cessna 182Q had been in the traffic pattern at Gillespie performing touch-and-go landings and takeoffs and departed the traffic pattern at 1638 southbound toward Brown Field. The airplanes collided about 2,300 feet mean sea level (msl) approximately 3 miles south of Gillespie.

A witness, a professional airline pilot, was sitting in his uncle's backyard on Mount Helix when he witnessed the event. He noted two airplanes were flying at an estimated 1,800 feet msl. One airplane was flying southwest bound. The other was flying east. They were both high-wing airplanes and one appeared to be larger than the other, similar in size difference between a Cessna 152 and a Cessna 172. The airplanes were in the Gillespie Field class Delta airspace when the airplane flying eastbound impacted the airplane flying southwest bound. The eastbound airplane impacted the right side of the southwest bound airplane.

Back to Top

ACCAR Relevance

The IFR 172 was only flying from Gillespie Field (387 ft) to a destination Brown Field Municipal Airport (526 ft) SDM 15 miles away, almost due south, about 183 degrees. The 182 was headed from Gillespie Field to the same destination. The collision was at 2300 MSL per FAA radar records. While both had a common destination and departure airport, the witness says one was SW bound, the other was E bound. The 172 took off at 1637 or 1638 (departed/cleared for TO--inconsistent account), the 182 left the pattern at 1638, with the 182Q leaving from pattern touch and go practice, and the 172 leaving from the runway, meeting at 1642, 4 minutes later. The higher 182, presumably faster, climbing only about 1000 ft, caught the 172 that had been slowed by its 2000 ft climb. Both were about 2000 ft AGL for about an 8-minute flight time between airports, so level flight cruise mode may have been reached by both aircraft. The 2000 AGL collision could have reasonably been avoided with the cruise mode protection offered by ACCAR, which would have provided 375 feet of vertical separation.

Both pilots might have hoped for SEE tower to provide visual separation while they were well within the usual 5-mile radius and below the 3000 AGL limits of SEE controlled airspace, with the 172 IFR pilot hoping for "as available" separation advisories from VFR traffic, plus all other IFR traffic. In the real world of Class D airspace, "all the tower is required to do is handle sequencing of arriving and departing aircraft and traffic advisories" (Runway Incursions? by Paul Bertorelli, Aviation Safety, p 7, May 2000). Pilot hopes for external separation guidance may have contributed to pilots relaxing their visual scan for threat traffic. Additionally the 172 had just been handed off to the Southern California Terminal Radar Approach Control (TRACON) facility. Therefore the 172 was still inside SEE volume on one frequency while the 182 was presumably still monitoring SEE tower on another frequency. It is possible that both pilots were preoccupied with getting ATIS for SDM, as required prior to contacting SDM tower. They may have compromised their visual scan for midair collision threats long enough to get their radios set up for the approach to a tower-controlled airport only 15 miles to the south of SEE.

Back to Top


Source

NTSB Identification: ANC06FA048A/ANC06FA048B, Sunday, April 23, 2006 in Chugiak, AK
Aircraft: Cessna 170B: N4488B
Cessna 172: N5049A
Injuries: 5 Fatal.

HISTORY OF FLIGHT

On April 23, 2006, about 1158 Alaska daylight time, a wheel-equipped Cessna 170B airplane, N4488B, and a wheel-equipped Cessna 172 airplane, N5049A, collided in midair, approximately 7 miles north-northwest of Chugiak, Alaska. Both airplanes were being operated as visual flight rules (VFR) personal flights under Title 14, CFR Part 91, in visual meteorological conditions when the accident occurred. The certificated airline transport pilot, and the three passengers aboard the Cessna 170B, sustained fatal injuries. The sole occupant of the Cessna 172, a certificated commercial pilot, also sustained fatal injures. Both airplanes were destroyed during the midair collision, uncontrolled descent, and subsequent collision with tidal mud flats. Both airplanes were based at the Birchwood Airport, Chugiak. The Cessna 170B departed from the Birchwood Airport about 1153, and a VFR flight plan was filed for the flight to Talkeetna, Alaska. The Cessna 172 departed from the Birchwood Airport at an unknown time, for a local area flight.

During on-scene interviews with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on April 23, witnesses reported that they observed the Cessna 170B traveling northbound, between 1,500 and 2,000 feet msl, and a Cessna 172 traveling in a southeasterly direction. About 30 seconds later, the witnesses described hearing a "loud explosion" which directed their attention almost directly overhead.

During a telephone conversation with the NTSB IIC on April 25, a witness who saw both airplanes just before, during, and after the collision, said that he witnessed the accident from his driveway, located about a half-mile north of the accident site. He said that as he watched the Cessna 170B fly northbound, at an estimated altitude of 2,000 feet msl, he observed the Cessna 172 traveling in an east-southeast direction, towards the Cessna 170B's left side. He said that as the airplane's flight tracks converged, and just before impact, he heard the Cessna 172's engine noise increase significantly, followed by a sharp nose-up maneuver. The witness stated that the Cessna 172 collided with the Cessna 170B's left wing, and left side of the fuselage.

According to a family member of the Cessna 172 pilot, the accident airplane had just undergone an annual inspection, and the short local area flight was the first flight after the inspection.

Back to Top

ACCAR Relevance

While this collision below 3000 ft AGL had no relevance to the hemispherical cruising altitude rules, it does demonstrate a missed opportunity for a collision that may have been avoided with ACCAR. A northbound aircraft and a southeastbound aircraft using ACCAR would miss each other by about 400 ft.

Notice that a witness described hearing the Cessna 172's engine noise increase significantly, followed by a sharp nose-up maneuver. With a nearly head-on closing rate of approximately 200 mph, the 172 pilot apparently noticed the 170B prior to impact too late to evade the collision. The "sharp nose-up maneuver" indicates the possibility that since the 172 had time to change pitch attitude enough to be noticed on the ground, then it is possible that the two aircraft might have missed each other if the "sharp nose-up maneuver" had not occurred. The change in engine sound prior to the pitch up maneuver hints at even more time during which the 172 pilot took some action on recognizing the threat. Unfortunately, a power change prior to the nose-up maneuver could not possibly have been as effective as doing the nose-up maneuver first, and then adding power.

Back to Top


Source

NTSB Identification: DCA06RA076A, DCA06RA076B Friday, September 29, 2006 120 miles east of Azevedo, Brazil, near Matupá
Aircraft: Boeing 737-800: PR-GTD
Embraer E135 Legacy: N600XL
Injuries: 5 Fatal.

HISTORY OF FLIGHT

On September 29, 2006, at approximately 1500 EDT, a Boeing 737-800 PR-GTD, operated by Gol Air, was lost in the Amazon jungle following a probable collision with N600XL, an Embraer Legacy E135, operated by Excelaire. The 737 was destroyed with 154 fatalities. The Embraer landed at Cachimbo air base with damage to the left winglet and left horizontal stabilizer. The were no injuries to the 2 crew and 5 passengers on the Embraer.

This accident is being investigated by the Brazilian CENIPA, Aeronautical Accident Prevention and Investigation Center.

"Gol Transportes Aéreos Flight 1907," Wikipedia, 18 November 2006.

The Gol 737 took off from Manaus, Brazil, destined for Rio de Janeiro, with a planned stop in Brasília. The Embraer Legacy business jet took off from São José dos Campos Regional Airport destined for Manaus. The southeast bound 737 collided with the northwest bound Legacy at FL370 (about 37,000' MSL) near Matupá. All 154 people on the 737 died. The seven people on the Legacy survived without injury. However, the left winglet and horizontal stabilizer on the Legacy were damaged. Both aircraft were recently manufactured, with a September 6, 2006, delivery of the 737 to Gol, and the new Legacy being delivered to the USA purchaser on this flight. The pilots of the Legacy reported that the TCAS system did not alert them to a traffic threat. The Legacy crew reported that at the time of collision, they had lost contact with Brasilia Air Traffic Control (ATC).

Back to Top

ACCAR Relevance

The Brazilian midair collision contained all of the most basic root cause ingredients of the German collision in 2002 and the Japanese near-hit accident in 2001. In both accidents, pilots were doing everything they were told to do by ATC, in some cases even to contradict TCAS conflict resolution instructions. The only difference is that in the Brazilian accident, the newest versions of TCAS equipment installed in both aircraft failed to provide any warning of the conflict. While the exact cause for the Brazilian TCAS failure has not yet been determined (18 November 2006), this apparent hardware failure causal factor may have been similar in result to a common contributing cause of the Denver midair collision in 2003, where a bad solder connection in the Cheyenne instruments eliminated the altitude display from Denver Center ATC consoles. Without the altitude information, automated conflict alert computer software was not able to predict the collision threat, and human intervention by the human controller in radio contact with both aircraft resulted in a verbal warning being transmitted to the Cheyenne pilot at essentially the same moment as the time of impact. In any case, Brazilian ATC failed to assign these aircraft safe flight paths, and then failed to detect the intersecting flight paths and warn the pilots in time to avoid the accident.

In the realm of a more fundamentally generic root cause analysis, the international aviation safety regulating community has failed to recognize the common cause linkage in the German collision killing 71, the Japanese accident injuring about 100 passengers (with 427 at risk), and the Namibian collision killing 33, i.e., that current regulations comprise a risk seeking system that unnecessarily concentrates cruising aircraft in artificially high density slabs of legal airspace, while wasting the illegal cruising airspace in between these legal altitudes in a way that maximizes aircraft collision target density. International regulators have failed to act on the fact that human and equipment errors are an expected, and not rare enough, part of normal flight operations. The current system allows repeat common cause accidents that could have been completely avoided with the Altimeter-Compass Cruising Altitude Rule (ACCAR), at zero cost to aircraft owners, pilots, passengers, and international regulatory agencies. They have tolerated a system with a "navigation paradox" recognized since the 1970s as rewarding random altitude poor piloting with more midair collision safety. With the fortunately rare, but expected failure of Brazilian ATC to provide safe flight path control (expected because Brazilian ATC cannot be expected to be better than Swiss or Japanese ATC), the most dedicated, skillful, experienced, professional commercial pilots accurately maintaining common altitudes ordered or allowed by ATC personnel are doomed to collide too unnecessarily often after a single mistake by ground control personnel. With apologies to alert and dedicated ATC personnel worldwide, this same system is likewise intolerant of single human failure event sequences in which one pilot makes an expected human error of flying at the wrong altitude either expected by ATC or required by the hemispherical cruising altitude rules. This single pilot failure scenario was the cause of the Namibian collision in 1997 killing 33, when the German Tupolev 154 aircrew flew accurately at the altitude reserved for opposite direction traffic, simultaneously being flown accurately by the pilot of at USA Air Force C-141 Starlifter. The failure of the international aviation safety regulating community to apply ACCAR after the above three common cause accidents has resulted in the death toll from those precursor events being more than doubled in a single repeat accident over Brazil.

The current regulatory practice requiring accurate flight at discrete cruising altitudes, when flown with zero altitude error, was proven to be about five times more dangerous than cruising flight at purely random altitudes in the 1997 Risk Analysis article by Robert Patlovany, and the independently corroborating 2000 Air Traffic Control Quarterly article by Russ Paielli. The ACCAR formula significantly improves on random altitude flight safety by systematically using all airspace volume to minimize aircraft collision target density, while automatically placing head-on traffic 500 feet apart and perpendicular traffic 250 feet apart. Contrast the ACCAR alternative with the current internationally accepted practice of deliberately flying aircraft accurately at discrete altitudes that are guaranteed to maximize collision probability after a single failure event or either human or hardware origin. The USA FAA failed to take action to eliminate the "navigation paradox" in ignoring Patlovany's recommendations supporting the ACCAR alternative in the request for a Notice of Proposed Rulemaking (NPRM), document No. FAA-2004-17079-1. After publication of the 1997 Risk Analysis proof that ACCAR has far better safety performance than the hemispherical cruising altitude rules, 342 people have died in over thirty easily avoidable midair collisions, i.e., easily avoided if ACCAR had been used for the flight safety of cruising aircraft at all altitudes.

Back to Top


Last updated November 18, 2006

1