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Falcon Targeting or Unraveling the Sensor of Interest (SOI) Mystery

Note: Please click on the smaller images within this article to view the full screenshots.

It was an easy target to see--the skeletal remains of several trucks in the center of a large plowed out circle on the Navy Dare bombing range. The last time I had tried using a Maverick missile on an F-16 was from an "A" model in Kunsan Air Base. A lot had changed in the "C" model F-16 (as I was about to find out). I decided to use the Boresight mode for the first few passes since I remembered it best from the F-16A. Along with being a simple point-and-shoot mode, Boresight was also very similar to the A-7's Maverick modes. I had just left the A-7 a few months before and still had some Corsair muscle memory that I had to work through.

Anyway, the first few passes were uneventful so I thought I would move on to the Slave mode. For this pass, I selected Steerpoint 9 (which was the center of the target truck array) and then went out 10 miles to get a good radar look at the target. The trucks didn't really stand out on the radar using DBS 2, but the circle around the target was easy to see so I placed my cursors in the middle of the circle and pressed in. At about 4 miles from the target, the trucks started to become visible in the Maverick video so I went to Expand in the Maverick MFD. I was now about 3 miles out, and in the Expand mode I could clearly see the target. I casually started to slew the cursor over the trucks to lock on and... the target disappeared. Just like that it was gone from the MFD. I was completely confused and starting to get concerned since the range to the target was closing fast. Since I slewed the cursors to the right and caused this problem, I decided to slew to the left and try to solve it. The target trucks passed through the MFD at the speed of stink and again were gone--this time out the other side of the scope. "This drill is getting me nowhere fast," I thought so I pulled off the target and decided to figure it all out later. Well, to get right to the point, I repeated the same mistake one more time before I really figured out that I had an SOI (Sensor of Interest) problem. I finally realized that the SOI was still in the left MFD where I had the Ground Map radar called up. I was slewing the radar cursors and not the Maverick tracking gate. Since the slew rates for the radar cursors are much greater than the slew rates for the Maverick, it was near impossible to get the target locked up in the MFD.

Well, virtually all F-16 pilots have their own SOI nightmare stories to tell. This Falcon Facts article will attempt to clear up the mystery surrounding the F-16 SOI implementation. First things first, though: let's start by discussing just what SOI or Sensor of Interest is. SOI is simply the sensor or weapons system that currently has priority. The following sensors or weapons can be the SOI:

  • Air-to-air radar
  • Air-to-ground radar
  • Maverick
  • Targeting pod (for laser-guided GBU bombs)
  • HTS (HARM Targeting System)
  • HUD

Why does the F-16 (and other modern fighters) have a Sensor of Interest? The answer is very simple, but the implementation of SOI is not. SOI is necessary because you can have more then one weapons system or sensor called up at one time. Notice that as you fly along in Falcon 4.0 and change to an air-to-ground weapon such as the Maverick, your radar changes automatically to an air-to-ground mode. The pilot, however, can change the radar back to air-to-air with the Maverick still called up in the MFD. In this case, which system are you using to point? That is what SOI implementation is all about: automatically providing the pilot the control over the correct weapon system.

How does the SOI move? Well, the SOI is automated which is both good and bad news for the fighter pilot. The good news is that it will generally be where you need it to be automatically. The bad news is that this automatic system can be befuddling. Both in the F-16 and in Falcon 4.0, I have had the SOI zing around the cockpit like a ricocheting bullet leaving me with my situation awareness down around my ankles. This article will try to track the elusive SOI in various modes and provide you some academic background.

The SOI moves between three basic locations: the radar (either air-to-air or air-to-ground), the HUD or a weapon mode. The weapon modes that can be the SOI are the targeting pod, the Maverick or the HTS. Remember only one location (radar, HUD or weapon mode) can be the SOI.

Well let's simplify things even more with a few SOI rules:

Whenever the HTS mode is called up, the SOI is always in the HTS MFD and cannot be moved.

SOI always in the HTS displayThis means that your HTS display takes complete control of the SOI. When you slew the cursors in the HTS display, the cursors in your radar display will not move. The SOI is in the HTS and will stay there. Figure 1 shows the HTS display with GM (Ground Map) radar called up.

If you have CCIP, CCRP or DTOS called up, the SOI stays in the radar.

In a Defensive Counter Air mission you job is to protect the AWACS or some other HVA (High Value Asset) from air attack. You do not have the same flexibility flying DCA as you do on a Sweep mission because mission success is tied to the survival of the asset. A DCA mission will have a route of flight as shown in Figure 1.

Whenever you enter the CCIP, CCRP or DTOS bombing modes, the SOI is the radar. This makes sense, but the CCRP mechanization can cause you problems. Although CCRP is primarily a radar bombing mode, it can also be used to drop bombs visually. In fact, in the CCRP training mission, you can look up in the HUD at the target and slew your TD (Target Designator) box over the target.TD box over the target in CCRP

This can lead to problems because the SOI stays in the radar. This means you have radar slew rates, even though in some cases you are slewing the TD box visually. Since radar slew rates are too high to use for HUD slewing, you need to be careful when slewing your HUD symbology in CCRP.

All we have left to discuss are the HUD and two of the weapons modes (since we already talked about the HTS). The two weapons modes left are the Maverick and the targeting pod. The good news is that both of these systems are very similar as far as SOI mechanization is concerned. The bad news is that the SOI mech for the Maverick and targeting pod is more complex. Let's start with the Maverick.

Maverick in the Boresight modeWith the Maverick, the SOI is either in the radar, the HUD or the weapon. The Maverick has two different modes: boresight and slave. When the Maverick is in Boresight mode, the SOI is in the HUD until the first designate (zero key on the numeric keypad). Remember when you designate the first time with the Maverick in the Boresight mode, you ground stabilize the Maverick. Two things happen at this point. The first thing is that the field of view for the Maverick or targeting pod gets tied to a specific spot on the ground (hence the term "ground stabilized"). The second thing that happens is the SOI switches from the HUD to the weapon MFD.

Where is the SOI when the Maverick is in the slave mode? The answer is "It depends." It depends on if your air-to-ground radar is locked on or not--which brings me to another SOI fact.

When the Maverick is in Slave mode, the SOI starts in the air-to-ground radar. When you attempt to designate (zero key on the numeric keypad), then the SOI moves to the Maverick MFD. The SOI stays on the Maverick display unless you break lock (by pressing the period key on the numeric keypad).

Figures 4 and 5 show before and after air-to-ground radar lock-on. You can see how the SOI moves from the radar to the weapon after the radar is locked on the target.

GM radar in the sweep mode To recap Maverick SOI, in the Boresight mode, the SOI stays in the HUD until the first designate (zero key on the numeric keypad). The SOI then moves to the weapon display on the MFD. If the Maverick is in Slave mode, the SOI is the radar until you designate with the air-to-ground radar. The SOI then moves to the MFD Maverick display.

The targeting pod works exactly the same way as the Maverick. The only small exception is that you cannot slew the targeting box in the HUD when you have the targeting pod in the Boresight mode (as you can with the Maverick in the Boresight mode). This is only a minor point, and you do not need to have a cranium meltdown at this point in the unlikely event that you have been able to understand this article so far. Just think of SOI mechanization working the same way for both the Maverick and the targeting pod.GM radar locked on

Well, that's about it for SOI. I know this subject is complex so I have intentionally shied away from it. In fact, I only started writing this article after I saw just how darn hard it is to make crossword puzzles. I'm sure not going to try that crossword puzzle stuff again unless I get No. 19 to do most of the work. Anyway, back to SOI. The only sure-fire way you are going learn this material is to go over it a few times and then fly it. I know it would help if I could get a nice treat to come out of your computer every time you did it right, but we haven't figured out a way to incorporate that in real F-16 training yet either. When we do, you will see a revolution in fighter pilot ability. Anyway, until next time... fly hard, shoot straight.

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