“Casual” Intercept: Simplified Intercept Procedure

Video

I put together a short video related to this article, as seeing the procedure from the point of view of the RIO makes it easier to understand.

Background and Context

After discussing Drift, TA, ATA and related concepts I had an interesting conversation about the possibility of using these concepts to perform an intercept, without spending a lengthy amount of time studying the Intercept Geometry. In particular, how they can help to understand and improve the performance in a BVR scenario. A pattern I noticed: new players especially have the tendency of putting the target on the nose, go pure pursuit, and chase the squirrel. This often leads, however, to the non-ideal situation of having the target drifting hard, the missile employed has to correct its trajectory and, by doing so, it bleeds a lot of energy.

So I took it as a for-fun-sort-of-personal-challenge: allowing pretty much anyone to perform an intercept using only a basic understanding of the avionics and without the complexity of the Intercept Geometry.

That’s the “inspiration” behind this simple article and related video: how to set up a collision course without diving into the details of the Intercept Geometry. So, forget the theory, we’re going full Eyeballs Mk I on this one! In case you are looking for the maths and details of notions such as Cut, DTG/HCA, LS and space management, do not worry, these topics will be discussed in details in the next chapters of this series.
Now, before getting overexcited by the perspective of not having Euclid around for once, there are some concepts that must be understood. In primis, the Drift: we know that, when the collision course is established, there is no drift. The idea is, therefore, manoeuvring until we end up with zero drift. Two displays are used to achieve this scenario: the TID, mostly in Aircraft Stabilized mode and the DDD. I profusely discussed the TID already, both mentioning how the Aircraft stabilized mode works and when I mentioned how it can be used to improve the SA just by looking at the contact’s vector.

The DDD instead is often overlooked, but it is an incredibly useful display.

The DDD to monitor Drift

The Digital Data Display is a B-scope placed above the TID. It is considered as the “raw output” of the radar. The details of this display are in the manual, so there is not much point in discussing the DDD. Nevertheless, the reason why it is mentioned here is because it is quite similar to modern attack displays when used in pulse mode as it provides a range vs azimuth view, making assessing the Drift a simple operation. For example, the contact in the image below is on a collision course as it is not drifting as the SR decreases.

Collision Steering

This is very handy function that, technically, should solve most of our issues. Unfortunately at the moment it seems inconsistent but, even when fixed and working, it has a couple of drawbacks:

  • if used in STT, this mode can alert the target of our intentions;
  • if used in TWSA, it suffers due to the number of ghost tracks that can confuse the calculation of the centroid, on top of the WCS itself that tries to include as many non-friendly contacts as possible.
  • on the other hand, when used correctly, it will absolve the RIO of having to track collision

This function can be activated by means of a dedicated button placed on the right of the TID.

Purity Obsession

Before diving into the geometry, a parenthesis about the most common “road” used to close the distance between the fighter and the target, especially by new players: Pure Pursuit.
New players especially have the tendency of using the pure pursuit almost constantly. Generally speaking, out of the three typical pursuit techniques (Lead, Pure, Lag) it is probably the one that works more often and it is simpler to set up and control: lock a target, place it in the middle of the HUD and follow it to the bitter end. But how does flying a pure pursuit impacts the intercept?

In primis it is not a cutoff. Therefore, if the target is a bomber or an AG aircraft, by the time we reach it, it may be too late as we are not placing the fighter between the hostile and its target, rather “spectating” as we get closer. It also has the tendency of placing the fighter towards a TA equal to beam or flank if the initial TA is greater than 30°-35° (the SR is another important parameter).

The “Casual” Intercept

By means of the concepts discussed so far we can come up with an incredibly simple intercept procedure that requires nothing more than a glance at the TID. Let’s start with a simple scenario, the same often used to introduce the intercept geometry (such as in the ubiquitous CNATRA P-825): the fighter and the target fly co-speed and co-altitude.
Therefore, the necessary steps are:

  1. Match altitude;
  2. Match speed;
  3. Manoeuvre to have TA = ATA;

And the objectives are:

  • Monitor drift;
  • Manoeuvre to have the Vector in TID AS pointing towards the F-14.

This allows you to fly until you “run into” the target (as per definition of collision course) or get close enough to VID or turn behind the target.
Each of the required parameters can be adjusted in just a few seconds.

Matching Altitude

This is very straightforward, the only parameter that may have an effect is the QNH (unless the intercept happens at ground level where masking or collision can be factors).

Matching Speed

Altitude and Speed can be obtained from the TID. Target’s speed can be provided by the controller (although usually by means of brevities). If GS is what you have, remember that the ECMD provides TAS and GS.

TA = ATA

When flying co-speed and co-altitude, the modules of the Target Aspect Angle and the Antenna Train Angle are equal. Thanks to the TID AS, there is no need of any calculation, what matters is where the target is presented on the TID. In fact, when the Vector points towards the F-14, the drift is null and collision course is achieved.

Example

This is not a precise intercept as my F-14 flew about 1.5nm in front of the target, as Iceman does not allow fine adjustments in terms of degrees. Nevertheless, it shows how the collision can be achieved in a very simple means even by now knowing much on the matter (so, no evaluations of TA, Cut, DGT/HCA and so on).

I highlighted the corrections. The original heading is in red, green for the first correction, light blue for the second and yellow for the final heading.

Note how the corrections were less pronounced the more I got closer to a satisfying picture on the TID. Without going a bit deeper into the intercept geometry (spoiler: CB = Cut/2) this is the simplest way to reach our objective.

Something slightly more complex. Or is it?

Even in a more casual environment, we hardly fly co-speed with the target. Imagine a scenario where the task is intercepting a bomber or some Fleet defence mission. In these cases, we will probably fly Buster, if not Gate. How do we deal with such scenarios? Simply put, exactly as we dealt with the scenario above, although the heading should be adjusted in order to compensate for the acceleration. As this procedure relies on glancing the TID, the heading can be adjusted in a matter of seconds, no Maths involved (for the moment 😛 ).

In this example the adjustments and corrections made as the F-14 was accelerating are clearly visible. Once the fighter reaches top speed, then the adjustments are less pronounced.

Note: the problem of the wrong/not updating tracks

As you probably have noticed in your usual flights, the track built in TWS is not consistent as the F-14 manoeuvres. I do not know if it is a bug or a limitation of the platform that sometimes requires a grater number of radar sweeps to update the track, but it can cause the RIO to over-correct. A simple workaround consists of deleting the track by means of the CAP and it will soon be recalculated, faster then simply turning the antenna in another direction.

Collision to Employment: Does it help?

The elephant in the room is whether this intercept satisfies the requirement of achieving a positional advantage, which usually means firing a missile with decent PK on top of other things. Let’s review the fist scenario seen above when employing an AIM-7 and an AIM-54.

AIM-54A Mk60 launched from CB at 35nm
AIM-54A Mk60 launched from CB at 45nm
AIM-7M launched from CB

The answer is… well, not amazing (the scenario flown does not help either). This method in fact does not do anything to achieve an advantage in terms of position: if you happen to have the target with TA ≤ 35° (close to hot), then the missile will be employed in “good” conditions. Otherwise, it may have to perform sustained or hard corrections, which have the tendency of bleeding off a lot of the missile’s energy (especially in the case of the AIM-54).

In fact, learning how to manipulate the Lateral Separation and obtaining spatial advantage is probably the hardest (at least initially) yet most interesting aspect of the Intercept Geometry. This does not mean that there is no simpler solution. As we did before, we can use a bit of ingenuity to correct the situation and place the aircraft in a more favourable position for missile employment.

Determining TA

In primis let’s clarify what the ideal situation is, from the point of view of the missile: the missile, in fact, performs better as the TA tends to zero as no corrections are required. On the other hand, creating a spatial offset is always recommended as manoeuvring space = options, and options are good. For the sake of this test, let’s say that we want to employ with TA close to the “Hot boundary”, therefore 30°TA, or 150°AA.
This leads to two other questions:

  1. How is the TA determined?
    There are a number of answers to this question, even Maths work but the simplest are:

  2. How can the TA be manipulated, in a simple manner?
    As for the previous question, there are a number of solutions, but the simplest is probably cranking: therefore, placing the targets on the gimbal limits (therefore in the Hot side of the TID AS) and keeping it there until the TA satisfies our requirements. This is not always applicable of course, as it depends on the scenario, but usually it works quite well and it is simple to achieve, with the benefit of maintaining SA on the target. If necessary the target can be even placed at 5-7 o’clock to further increase the impact on the TA but it can be a dangerous game as the fighter loses SA of the target.

A Solution. Sort of…

The approach just discussed is similar to the one used during the transition between BVR and WVR, but at a greater distance.
The following two examples show the AIM-54A Mk60 fired at 35nm and 45nm:

AIM-54A Mk60 launched post crank at 35nm
AIM-54A Mk60 launched post crank at 45nm

How much energy has the missile gained? Since there was little time to manoeuvre in an optimal position (and reducing the TA even more), due to the distance and speed of the target, not much. The missile hits the target whilst flying only M.3 faster. Interestingly, the missiles employed post-crank have reached the target a few seconds sooner, which is also important as the missile has to be sustained until pitbull.

The outcome can be improved by, for example, going Gate (in these examples I accelerated during the crank but decelerated prior to employment to minimize the impact of the energy on the results). Another means is having a human pilot, as Iceman turns in literally ages, wasting time and space.

Pure Pursuit: observations

Out of curiosity, I also replicated this scenario using a Pure pursuit right from the start. The outcome is definitely unexpected: I had issues as the contact was notching the AWG-9 first, then the AIM-54 as well. I also tried by means of PSTT to minimize the problem, but PSTT does not control the loft, severely impacting the performance over greater distances.

AIM-54A Mk60 launched following pure pursuit at 35nm
AIM-54A Mk60 launched following pure pursuit at 45nm
AIM-54A Mk60 launched following pure pursuit at 35nm (STT lock)

I run a couple of additional tests and the results either match the performance of the Collision (as TA tends to zero) or a straight out worse (especially as TA > 45°). It does make sense if you think about it: collision “cuts” the flight path of the target, pure follows the target but, in order to do so, it requires constant corrections as the target is constantly drifting.

This last image is the comparison between the three employments:

AIM-54A Mk60 at 35nm: “Crank” vs Collision vs Pure pursuit

Interesting, isn’t it?

Conclusion

The examples shown above of “Casual” intercept do not provide results as controlled and precise as the actual procedures. You may have noticed in fact how these approaches result into different “impact” angles every time, require numerous adjustments and do not place the fighter in the optimal conditions for a missile employment, not to mention any stern conversion turn.

However, there are some pros in this empirical way of doing the intercept. In primis it is very easy to use: just place the target’s vector towards the F-14 in TID AS and that’s pretty much it, and this was the main objective of the Challenge. Therefore, it does not require specific, lengthy and detailed study.
It also helps to improve the SA: just consider how AI hostile fighters have the tendency of placing their target on collision; now you can tell if they are placing your aircraft on collision just by glancing at the TID AS.
This procedure has also shown a very simple mean to manipulate the geometry by placing the target at the limits of the radar and accelerating.
Lastly, this is a valid alternative to the common Pure pursuit.


I hope you enjoyed this unusual article and, perhaps, learnt something new!

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