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Intercept Geometry – Part VIII: Intercept Progression & Lead Collision [P-825/02]

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The second half of the P-825/02 covers a variety of advanced procedures and techniques. Discussing all of them will be way too long, so this article and the next are a brief overview of a limited set of those concepts. In particular, this article covers the Intercept Progression and the Lead Collision.
Intercept Geometry: Table of Contents

In Short

This article applies the notions and the definitions discussed before to scenarios of increasing complexity, adding more concepts and eventually providing a more structured and concrete application.
At the end of Part IX, everything discussed so far will be used to introduce the Advanced Intercepts, versus non-cooperative targets.

Note: most of the content of this article and the following have been discussed already. The second part of the P-825/02 is, in fact, a re-elaborated presentation aiming to provide more structure to the concepts. For that reason, I decided to summarize the topics as much as possible, sometimes using simple bullet lists or tables.

Intercept Progression

Now that different parts of the intercept have been refreshed and discussed (Part II: Definitions and the ensuing Part III: Lateral Separation and Target Aspect should be reviewed before proceeding), we can have a look at how the P-825/02 proposes the Intercept Progression.

Initial Phase

To clarify the goal and the flow of the Intercept Progression, better quote the documentation directly. Remember that these are IQT / Basic procedures, so the game plan is never too complex (at least at this stage):

“First of all, the term reattack refers to the breaking-off of a collision intercept after either employing a forward quarter, radar missile (“attack”) or having forgone the beyond visual range (BVR) missile shot, proceeding to displacement and executing a counterturn to arrive in the rear quarter with a second shot opportunity (“reattack”). The pursuit intercept is executed in the same way as the reattack except it is done entirely in PLS, holding the radar lock (STT) until just before the rear quarter shot.”

CNATRA P-825/2; p.85

The initial phase of the intercept sees the RIO using the information provided by the GCI to determine the Target Aspect and calculate the collision course. Once the collision course has been established and verified, the aircrew will make a contact call. If the CB is not established, CCC (Collision Course Correction) is required. The CCC procedure can be stopped due to timeline (see next Phase).

Mid Phase

This phase is dedicated to planning and observation.
At 15nm, the AREO report starts, essential to help the pilot to visualize the intercept. The RIO continues to monitor the collision. Two miles before the DT (Displacement Turn) range (10nm or 12nm), the Target Aspect value should be finalized. The RIO also has the task to appropriately describe the displacement point and counterturn fitting the gameplan. Note that displacement range and displacement points are based only on Target Aspect.
2nm before DT range, CCC is chased, any drift is noted (it must be taken into account during DT and CT) and the altitude difference is analysed.
The DT is not commanded by the RIO through angles, rather using:

RIO ► Left/Right hard for Displacement

Then, to command the roll-out, the usual

RIO ► Steady Up!

Final Phase

At DT, the focus shifts from proper TA analysis to drift control:

  • When TA 0-15 → no inward drift can be accepted prior to passing 180 DTG (ergo FH=BR) in the CT;
  • When TA ≥ 20 → no more LS can be gained, the bogey can be allowed to drift on the nose.

The goal is arriving in a “window” where the bogey is on the nose with 90 DTG (FFP ⟂ BFP) and the RIO should use the appropriate commands during the turn to keep the bogey as close as possible to the nose.

Radar Lock

Ideally, radar lock should be obtained before rolling out in the RQ. The suggested criteria for locking up the bandit are:

  1. Through the 90 DTG position;
  2. Hard turn or less;
  3. Drift stabilized;
  4. Good spotlight.

“Passing the dot”

When VC < 100 kts, the control of the intercept can be passed to the pilot.
The criteria for this step:

  1. Bandit locked (STT);
  2. In range (½ to 1½ nm);
  3. Pitch ±8° (dot inside the ASE circle);
  4. Azimuth ±8° (dot inside the ASE circle);
  5. VC between 0 and 100 kts;
  6. Drift stabilized;
  7. Hard turn or less.

Intercept Sequence

The last paragraph of the Intercept Progression discussed in the P-825/05 is quite interesting (p. 88):

“[..] the weapons officer must manage the dual tasks of stabilizing and controlling a very dynamic situation while physically manipulating the radar. These tasks are delineated below. The left-hand column represents the actions required to control the geometry while the right-hand column lists the tasks associated with operating the radar and making the necessary commentary. It should be re-emphasized that a logical, disciplined approach is the only way to satisfactorily control the numerous variables of the airborne intercept.“

CNATRA P-825/2; p.88

I am reporting the aforementioned table in its entirety.

Search Mode Sequence
  • Check level antenna prior to first run;
  • Adjust video and gain controls for optimum scope presentation.
Range
Intercept Procedures
Radar Functions
At range
  • GCI info (BH & BB).
  • Compute BR, TA and CC.
  • Check RMI¹;
  • Confirm Cut/CC;
  • BRA upon contact.
  • Move antenna using proper search instruments;
  • Select proper range and sector scan;
  • Attempt STT.
15-10 nm
  • Check MB calls from GCI for drift that requires CCC.
  • Confirm Cut on RMI.
  • Confirm bogey on CB, make CCC if necessary;
  • Evaluate and give game-plan Concerning DT and CT;
  • Stop CCC 2nm prior to DT;
  • Begin climb / descent do 1000ft above or below bogey altitude² (with radar contact). Do not cross bogey altitude without tally!
  • Continue to move the antenna by appropriate increments (no STT);
  • Adjust video and gain if required;
  • Give AREO reports if painting bogey;
  • Move antenna to fine tune to spotlight (no STT);
  • Note bogey elevation / altitude.
10 / 8 nm
  • Displace bogey to desired ATA.
  • Execute desired CT.
8 – 1 nm
  • Execute desired CT.
  • Fine tune bogey altitude and climb or descend with tally;
  • Note range approaching 90 DTG for possible use of BUSTER³;
  • Control drift and stabilize RQ.
  • Shoot when parameters are met.
  • Give Directive commentary in CT to control drift. Spotlight or continue search as required.
  • Give abbreviated AREO.
  • Anticipate larger EL strobe movement
  • Lock bogey when lock criteria are met (if required);
  • Select Sidewinder with good STT.

¹ – Radio Magnetic Indicator.
² – VD will be discussed for all intercept techniques in a separated chapter.
³ – This indication refers to the aircraft in use in real training (T-39).

GCI Intercept Progression

Although rare in DCS, there can be occasions where the intercept has to be completed using only the information provided by the GCI. This eventuality, of course, excludes the scenario where the Controller is an AI.
Examples of those eventualities are:

  1. Radar degradation or failure;
  2. The need to suppress radar signals from the fighter that may set of the enemy’s RWR / RHAW;
  3. Electronic jamming emissions that degrade the fighter’s radar picture.

As mentioned, the scenario discussed in this chapter is a rare occasion. In primis a capable human controller is needed, moreover Point #1 is not applicable as very rarely random failures are enabled outside training (the only situation I can think of is the case of damaged induced by pulling too many Gs). Point #3, jamming, is not implemented yet outside a very basic and rudimentary form, so it is de facto a non factor at the moment of writing this article.
Point #2 instead is definitely be more applicable, but the ubiquitous datalink usually compensate for the non-XMIT radar.
Nevertheless, this is a very interesting topic, and it is worth having a look at how an intercept can be performed without the use of the radar, even in a superficial way.

Intercept Flow

  1. Collision Course

    The bandit can be placed on Collision Course independently of the status of the radar. The formula used is BR → BB → CH.
    However, the drift is not directly assessable, so the evaluation is made using the GCI calls and re-employing the same formula to correct the collision.

  2. Displacement Turn

    When the drift is stabilized, at a range that depends on the Target Aspect, the DT is executed using the methodology discussed in the normal DT.

  3. GCI Counterturn

    This last step is potentially the most complex as the normal cues of VC and intercept drift are not present. The CT should follow the pattern for the ideal curve, a function of the current Target Aspect.

  4. GCI Rear Quarter Drift Control

    The goal at this stage is to prevent the fighter wave. This is accomplished by using no more than standard turn, as post 45 DTG, and with bandit within 20° of the nose, the drift decreases rapidly.

Lead Collision Intercepts (Attack-Reattacks)

So far, a great deal of space has been occupied discussing RQ missile employment. However, the vast majority of the missiles launched are closer to the front quarter. This is even more true in DCS, as the AI sees everything, AWACS are everywhere and the ROE are often a simple Friendly vs Hostiles. However, if you are lucky enough to fly in a squadron or wing that put emphasis in realism you may be required to intercept with the purpose of VID first, rather than simply shoot a bleep on your radar screen out of the sky.
When the latter is not the case, missiles are usually employed from the FQ. A technique used to improve the odds of the missile to hit the target is discussed below and covers the employment of the AIM-7, the main missile employed by the US until the AMRAAM superseded it.

Although the documentation does not consider the scenario of an AIM-54 employed in STT, hence behaving as a SARH missile, the Lead Collision is still very much applicable and useful to preserve the energy of the missile. The only difference is the speed of the missile itself: being so fast, the angles suggested for the AIM-7 may not be the most suitable, but it is still better than employing from CC.

Factors Affecting Success

The AIM-7 is employed with the radar in STT mode, to provide the necessary continuous wave guidance to the missile. The F-14 can also employ the AIM-7 in Pulse Doppler mode, if the RIO decides so.
Factors that can improve the odds of a missile are many, the most important is the Rate Of Closure. The VC is higher when the Target Aspect is lower and this facilitates the job of the radar, as it uses Doppler frequency shift for their targeting. The VC also determines the maximum range and the probability of kill ( PK ) of the missile.

Lead Collision

In order to increase the VC the fighter can make the missile fly faster, fly the aircraft faster or lower the TA. The documentation covers only the last point, but the first two are both connected and intuitive.

TA manipulation is a topic already discussed, but there is a new concept to introduce: the Lead Collision. LC is a form of Pure pursuit that facilitates the missile’s job by making it fly its own Collision Course towards the target. The scenario is similar to a fast fighter vs a slower target and the geometry must be changed accordingly. In particular:

  • TA > fighter’s ATA;
  • the target is inside the CB and will drift away, resulting in the TA increasing over time;
  • the missile is on CC with the target.

The idea is manoeuvring to achieve Lead Collision right before RMAX in the quickest way possible, so that the missile will be on collision with the target at or inside RMAX.

Lead Angle Off (or Lead ATA)

Due to ΔV > 0, the intercept isosceles does not exist. This is the same situation that occurs when VF14 ≠ VTGT, a situation not covered by the documentation, but we tried to partially address it ourselves.
In this scenario, the ATA is called “lead” when the fighter is in the correct position for firing the AIM-7. The WCS will also provide the necessary steering information to the aircrew for this ATA. The crew can use the usual ASE Circle to steer to the correct position.

Symbology for PSTT and PDSTT radar modes.

Effect of LC on TA and ATA

Lead Collision implies, in co-speed scenario, that TA ≠ ATA, hence introducing drift. The Lead Angle Off is displayed by the ASE circle but, for the AIM-7, it is generally close to ½ the Target Aspect at RMAX, when 0 < TA < 47°.

The lower TA means higher VC, and therefore higher PK.
The following table shows the reference values of TA and Lead ATA:

TA STOP CCC LEAD ATA FOX-1 RNG MIN DT
0° 14 nm DA 12 nm 8 nm
5° 14 nm 2½° 12 nm 8 nm
10° 14 nm 5° 12 nm 8 nm
15° 14 nm 7½° 12 nm 8 nm
20° 14 nm 10° 12 nm 8 nm
25° 12 nm 12½° 10 nm 6 nm
30° 12 nm 15° 10 nm 6 nm
35° 12 nm 17½° 10 nm 6 nm
40° 12 nm 20° 10 nm 6 nm
45° 12 nm 22½° 10 nm 6 nm

Lead Angle & Dot Relationship

The dot in the ASE represents the correct Lead ATA or Lead Angle Off (with 3° of tolerance). The dot is six times more sensitive, so the ASE circle is +18°.
The dot is aircraft stabilized, indicating which attitude to position the nose to achieve the correct solution.
A peculiarity of the dot is an “ATA-dot” prior to Lead Range, telling the crew where to turn for collision. At Lead Range it becomes a lead computing “Steer to dot”, in order to manoeuvre the aircraft in firing parameters.

The turn to LC is usually standard if greater than 5°, otherwise it is an easy turn. Commands will be “Left/Right for lead” and “Steady Up“. In the training scenarios described by the P-825/02, when the conditions are met, is the student that hands over the control to the front seat by means of the call “Your Dot“. The pilot will then call the Fox-1 launch.
In DCS, the last part of the LC can be settled with a crew contract. Nevertheless “leaving the dot” to the pilot allows him to quickly manoeuvre the aircraft in the best position for the employment.

Conditions of Launch

The following table cover the four conditions that may exist when the target is taken to lead.

Condition Shot? Action
Target ATA within ±3° of Lead ATA & dot in circle Valid Call “Your dot” and shoot the AIM-7
Target ATA within ±3° of Lead ATA & dot out of circle Invalid
  1. Wait until min Displacement Range;
  2. If dot above or below ASE circle, call for “Nose high/low for the dot“.
Target ATA outside ±3° of Lead ATA & dot in circle Invalid Re-lead the target to get within ±3°
Target ATA outside ±3° of Lead ATA & dot outside circle Invalid Re-lead the target to get within ±3°

Sidewinder Reattack

Post Fox-1, the fighter may displace immediately and with no delays.
The reattack follows the same modus operandi described before. However, a new concept is introduced, the “Minimum Displacement Range“: if a fighter waits for the dot to drift into the ASE, the DT may be delayed until this new range. If the DT is delayed past this range, the fighter will have to compensate for the consequent “hot” approach. As a rule of thumb, over-displace 5° per 1nm of delay to cool the intercept. Then, when passing through 90 DTG, the pilot is commanded to “Select Sidewinder” and the shot can be taken using again the same criteria discussed before.
Note: the reference Minimum Displacement Range values (Min DT) are displayed in the table above, in the paragraph “Effect of LC on TA and ATA”.

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Published by Karon

Software developer, flight sims addicted since forever. I opened flyandwire.com initially as a personal repository for my Arduino articles and firmware, later to share my passions to other fellow hardware & flight enthusiasts.