Final Rapport




  1. DC-10 route.
  2. Transcription of radiocommunications with N'Djamena.
  3. Parameters recorded by the DFDR and analysis of the abnormal values (peaks) that were found.
  4. Model showing aircraft detachment.
  5. Distribution map of the debris.
  6. Distribution map of the major parts of the main wreckage.
  7. Position of the containers inside forward cargo hold.
  8. Reconstruction of the fuselage section - main damage to the pressure hull.
  9. Glossary of the abbreviations.
  10. Photographic documents


Dc-10 Route



12.00 UT 772 N'Djamena UTA 772
  NDJ UTA 772 N'Djamena
  UT 772 Yes, we are ready to start-up to Paris.
  NDJ Roger, start up, temperature 33, dew point 22, Fox Echo 9. 7.5. and QNH 1010, the 23, report to taxi.
  UT 772 Yes, starting up, call you back to taxi UT 772. We'll take the 05 if possible.
  NDJ OK for 05, report to taxi.
  UT 772 Willdo.
  N24RM N'Djamena N 24 RM evelling at 095.
  NDJ 124RM report TMA out.
  N24RM ....
12.02 UT 772 Last wind for UT 772.
  NDJ 220 240 6 to 8 knots.
12.08 UT 772 N'Djamena UT 772 we are ready to taxi.
  NDJ 772 taxi mid-taxiway, enter and back track.
  UT 772 So, we taxi via mid-taxiway and back track 05.
  NDJ OK for 05.
12.10 NDJ 772, clearance.
  UT 772 Go ahead Sir.
  NDJ Left turn after take-off, initial climb to 280 by BOSSO.
  UT 772 Roger left turn after take-off and climb to 280 initially BOSSO UTA 772.
  NDJ Correct and report lined up to take-off.
  UT 772 I call you lined up.
12.12 UT 772 N'Djamena UTA 772 to take off.
  NDJ 772 Clear to line up and take off 240,6 knots.
  UT 772 772 taking off runway 05.
12.16 NDJ UTA 772 take-off at 13 call back for estimates.
  UT 772 Roger.
12.17 UT 772 Ready for estimates ?
  NDJ Go ahead.
  UT 772 Well BOSSO at 12.35 hrs FIR flying out at 13.10 hrs arrival at Paris Charles de Gaulle at 17.19 hrs one seven one nine, we pass level 70 climbing to 280 initially.
  NDJ Roger 772 report passing 240 to climb.
  UT 772 Affirm report passing 240 to 280.
12.22 UT 772 N'Djamena UTA 772 approaching 240 to 280
    FREQUENCY 128.1
12.23 UT 772 N'Djamena Info UT 772 good day approaching 240 to 280 initially.
  NDJ UTA 722 good day report 280.
  UT 772 Roger. Request higher.
  NDJ Yes. Giving you a traffic information, Air Zaire 002 flying from Kinshasa to Brussels is at level 310 and ENBUT point estimated at one two two five at 12.25 hrs, INISA at 12.57 hrs, it is a DC-10, you report approaching 280 for higher.
  UT 772 Ok thank you.
  NDJ You estimate BOSS at 35 correct?
  UT 772 BOSSO at 34.
  NDJ 34 Roger. For the time I have no contact, report approaching 280. |
  UT 772 Roger.
  NDJ Zaire 002 N'Djamena
  AZR 002 Right N'Djamena we are checking ENBUT at level 310 .
  NDJ Roger report INISA.
  AZR 002 Read you 002.
  NDJ UTA 772 N'Djamena
  UT 772 Yes Sir, go ahead
  NDJ Report crossing 300 to 350.
  UT 772 Roger report crossing 310 to 350.
12.27 NDJ 002 checking ENBUT at 25 to INISA.
  UT 772 Roger contact with it. OK report three one zero to three five zero.
  AZR 002 Yes, for your information Air Zaire maintaining 310.
  NDJ Wilko, thank you.
  NDJ UTA 772 N'Djamena
  UT 772 Yes I read you.
12.28 NDJ Did you check KANO FIR boundary inbound point?
  UT 772 Affirmative.
  NDJ At what time ?
  UT 772 At 25.
  NDJ 25 thank you.
  UT 772 UTA 772 crossing 310 to 350.
12.29 NDJ UTA 772 report leveling 350.
  UT 772 OK, report 350 steady .
12.32 UT 772 UTA 772 steady level 350 BOSSO within 2 minutes.
  NDJ Roger, report passing FIR.
  UT 772 Roger.
  NDJ UTA 772 N'Djamena
  NDJ UTA 772 N'Djamena
12.34 UT 772 N'Dgamena UTA 772
  NDJ 772 I request coordinates of the outbound point on FIR boundary N'Djamena
  UT 772 Confirm ?
  NDJ Coordinate of FIR outbound points.
  UT 772 All right, that will be 18.07 north 11.30 east.
  NDJ Roger report passing the FIR on 8903.
  UT 772 Wilko. Making a relay for you.
  NDJ OK, transmit thank you.
  UT 772 Well it's S.A.Z. 01 flying Zurich-N'Djamena level 410. Checked TUMMO at 7 and estimates N'Djamena at time 13.42.
  NDJ Read well read thank you very much.
  NDJ He call me back DIRKOU.
  UT 772 DIRKOU ?
  UT 772 Sierra Alpha Zulu
  N24RM N'Djamena 24 Romeo Mike.
  NDJ 24 Romeo Mike N'Djamena.
  N24RM 24 RM we'd like descend from flight level 095 to 3,500 feet.
  NDJ Roger call maintaining 3,500 feet.
  N24RM OK 24 RM.


Curves 1 (208 Kb!)

Curves 2 (195 Kb!)


A detailed study of the DFDR read-out shows that these peaks were not due to variation of the actual values during the flight but rather to de-synchronisations of the signal during read-out.

1. How a DFDR works

To explain this de-synchronisation phenomenon, it is necessary to review DFDR data acquisition and read-out. Sensors on board the aircraft enable to get various data. The data is transmitted to computers that deduce the value of a number of parameters which are characteristic of the flight.

Those parameters (in analogic form) are then coded, digitised and multiplexed by a job-oriented computer, the Flight Data Acquisition Unit (FDAU) and transmitted to the recorder itself as a sine wave form signal.

Multiplexing consists in presenting one after the other (in the form of a continuous signal) various parameters which are obtained simultaneously.

As far as the DFDR is concerned, all parameters are given in frame format, each parameter being repeated at the same place (or same "word") in each frame. The frame used by the FDAU of the DFDR is a four-second one, each frame being itself divided into four one-second sub-frames. Each sub-frame must contain 768 bits (0 or 1), i.e. sixty-four 12-bit words, and must begin by a specific word called "synch word".

At DFDR read-out, a series of computers decode the data in the reverse way they were recorded. So, after the signal is read, a computer cut it and convert it into bits and words. Then those words are demultiplexed so as to be finally translated by one more computer into actual values (the flight parameters).

During the demultiplexing operation, there is a verification of the binary signal: the demultiplexing computer searches for all the synch words (as defined above) and verifies that the number of bits between them is correct. If, for any reason, (damaged tape, bad reading, etc...) a synch word is not to be found at the right place, the computer will warn that there was de-synchronisation when that sub-cycle was concerned; in such a case, the conversion of the binary signal into actual values will be altered and the listings and graphics obtained subsequently will show abnormal values. There will be synchronisation again as soon as the computer detects two synch words that define two consecutive sub-frames, separated by the right number of bits.

2. Analysis of the de-synchronisations

Let (tf) be the last recorded second of the flight; a first de-synchronisation is noted at (tf-14 seconds). A more accurate analysis of the binary signal read at that second makes it clear that 2 bits are missing in the sub-frame (766 instead of 768 bits) and that these bits were lost at the beginning of the sub-frame (starting from the fifth word). All actual values calculated later on are therefore distorted (more than 90% of the data contained in that second are lost).

A second de-synchronisation occurs at times (tf-11s) and (tf-10s). These two seconds are de-synchronised because the computer has not found the synch word which is between the two sub-frames. Nevertheless, the analysis proves that the first 46 words (out of 64) at second (tf-11s) are consistent; so are the last 60 words at second (tf-10s). Therefore something wrong happened between the forty-seventh word of time (tf-11) and the fourth word of time (tf-10).

Finally, a last de-synchronisation occurs at time (tf-5s). During that sub-frame, the computer counted 770 bits (i.e. two additional bits). As early as the sixth word of that frame, there is inconsistent information (one additional bit at that moment). If we make the assumption that it is one bit too many, consistent data is to be found again, through manual calculation, until word '9, and then there are again abnormal values.

In this way we note that, several times along the fourteen seconds before the end of the recording, the binary signal calculated by the DFDR shows alterations that bring about a translation in actual values that is utterly wrong and in no case representative of the actions of the aircraft at these moments.

Another reading of the DFDR was made with a different tension of the tape on the playback heads. It was then noted that two out of the three de-synchronisations of the tape end had disappeared (those at times tf-14s and tf-5s). The parameters recovered for those two seconds were perfectly consistent with the rest of the flight.

De-synchronisations on one listing, partial recovery of consistent data on another ones are the proof, if needed, that these problems are due to the bad condition of the tape.

3 . Explanation of these de-synchronisations

The DFDR recovered after the accident was particularly damaged (impact evidence, rounded sides,etc). When it was opened, BEA specialists noted that the thermal insulation was damaged and, furthermore, that the outer loop of tape was severed, that it showed folds and that is had come out of the roller transport guides. We may suppose that that section of the tape was cut at the ground impact, because it was less protected, and that the tape slackened suddenly and hit mechanical parts (rollers, playback head, etc...) The signal on the tape may have then be damaged; this deterioration of the sinusoidal signal may have led to a defective binary transcription.

This DFDR works in such a way that the last recorded seconds are precisely located between one of the erasing heads and the corresponding far left roller. Between those two points, the tape Ad about 30 cm long. Since the tape recording speed is 0.43 in./s the last twenty-seven seconds, or so, are on this section.

To investigate that problem, BEA carried out an extensive analysis of the end of the original tape . The use of a detector material on that tape section made the following apparent :

The beginning of the detected blank space precisely corresponds to the end of the flight recording . 5.2 cm before, ( i .e . a 4. 7 s. recording), an important folding enables an explanation of the de-synchronisation found at time ( tf-5s ) on the first listing. Then, 11.1 cm before the end of the flight (i.e. a 10.2s recording),, the tape was cut, which is an indubitable explanation to the de-synchronisation between times (tf-10s) and (tf-11s). Lastly, 15 cm before the end of the flight (13.7s), the fact that the tape was slightly creased also explains the de-synchronisation at time (tf-14s) in the first listing.


Model showing aircraft detachment


Distribution map of the debris


Distribution map of the major parts of main wreckage (Referenced C Appendix 4)

1 Lower fuselage skin
2 No 3 engine turbine compressor and cowl parts
3 Lower fuselage, fuel components
4 Drip No 9
5 Upside down right wing
6 Drip No 7
7 Engine cowls and pod
8 Slat part
9 Not engine component
10 Not engine drive
11 Fuel indicator
12 Main landing gear part
13 Cowls
14 Gear truck
15 Central landing gear door
16 Fuel tank
17 No 3 engine case and fan
18 Electric generator
19 No 3 engine component
20 Central landing gear door
21 No 1 engine turbine and combustion chamber
22 Wheels
23 Slat part
24 Main landing gear part
25 Gear truck
26 Landing gear box
27 Landing gear part
28 No l engine fan and compressor
29 Left wing tip
30 Upside down left wing
31 Landing gear doors
33 CVR
34 Part of aft fuselage from cargo hold level
35 Stabilizer component
36 Part of fuselage, tail cone, APU
37 Aft cargo hold floor
38 Stabilizer: central section and left part
39 Hydraulic tank


Position of the containers inside the forward cargo hold


a. Reconstruction of the fuselage section
(Reference B Appendix 4)
b-A. Reconstruction of the fuselage section
(Reference B Appendix 4)
b-B. Reconstruction of the fuselage section
(Reference B Appendix 4)
c-A. Belly aperture
(Reference B Appendix 4)
c-B. Belly aperture
(Reference B Appendix 4)
d-A. Reconstruction of container 7044 RK
(Reference B Appendix 4)
d-B. Location of container 7044 RK floor on cargo hold floor
(Reference B Appendix 4)



APUAuxiliary Power Unit
BEABureau Enquetes-Accidents
CEATCentre d'essais aéronautique de Toulouse (Toulouse Aeronautic Test Center).
CSSCertificat de sécurité sauvetage (Safety and rescue certificate)
CVRCockpit Voice Recorder
DFDRDigital Flight Data Recorder
DGACDirection Générale de l'Aviation Civile (Directorate General for Civil Aviation)
DNADirection de la navigation aérienne (Air Navigation Directorate)
FAAFederal Aviation Administration
FDAUFlight Data Acquisition Unit
FIRFlight Information Region
ICAOInternational Civil Aviation Organization
KSSUKLM-Swissair-SAS-UTA Group
NTSBNational Transportation Safety Board
RKAir Afrique designator
SIGMETSignificant Meteorological chart
SELCALSelective Calling
UTUTA designator
UTCUniversal Time Coordinated


1. Forward section (Appendix 4, referenced A)
2. Reassembled elements of fragmented section (Appendix 4, referenced B)
3. Main wreckage fire area (Appendix 4, referenced C)
4. Scattered elements Right stabilizer (Appendix 4, referenced D)
4. Scattered elements No.2 engine: air intake central section with fin (Appendix 4, referenced D)
5. Scattered elements No.1 engine air intake (Appendix 4, referenced D)
6. Evidences Metallic impact in wooden box cover
7. Evidences Torn clothes with holes

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Copyright © 1996-98 Harro Ranter/Aviation Safety Web Pages; Updated 19 April 1998