Intercept Geometry – Part V: DT, CT, Timeline [P-825/17]

Intercept Geometry: Table of Contents

Part I: Introduction
Part II: Definitions
Part III: Target Aspect & Lateral Separation
Part IV: Modern Gameplans (P-825/17)
Part V: P-825/17: DT, CT, Timeline
Part VI: Modern Intercept Demo Videos (P-825/17)
Part VII: 2000s Intercepts (P-825/02)
Part VIII: Intercept Progression & Lead Collision (P-825/02)
Part IX: “Unknown Procedures” & Fleet Conversions p1 (P-825/02)
Part X: Fleet Conversions p2 & Advanced Intercepts (P-825/02)
Part XII: In-Depth Timeline (from “Picture” to “Crank”)
Part XIII: In-Depth Timeline (continuation: FOX 3/1/2)

The Gameplans discussed in the fourth part of this series guide the fighter from an initial position, relative to the bandit, where its Target Aspect generally between 0 and 60, down to the last Gate at 10nm, where ideally 40,000 ft of Lateral Separation are achieved.
This article introduces the last step, namely the turn from the last Gate to the Rear Quarter of the bandit: the Counterturn (CT); on top of a contingency manoeuvre used to generate or remove LS in case the fighter was not able to meet the usual goal of 40k ft of LS at 10nm. This manoeuvre is the Displacement Turn.

Displacement Turn: the much-needed turning room

The Displacement Turn (DT) is a contingency manoeuvre in case the goal of 40k LS at 10nm is not achieved. Failing to meet the 40k LS goal leads to the non-ideal situation where the fighter may lack the manoeuvring space to re-orient itself behind the target. This situation may, since the LS may be even zero, cause an unaware bandit may become aware of the fighter. It can also make a tasked VID difficult or cause a merge to start in a less favourable position.

The Displacement Turn is a technique not used any more besides correcting a situation that should not happen in the first place. The DT sets three main objectives:

To create LS ideally close to 40k to enable the standard counter turn;
To ensure that radar contact is maintained through the manoeuvre, down to the employment;
To ensure that the fighter remains in control of the bandit TA at the intercept.

The Rule of 40

The so-called “Rule of 40” is used to measure the correction required to generate enough LS.

Target Aspect	LS at 10nm	Displacement ATA (40ATA Cold-TA)
0	0K	40 ATA, either side
10 L/R	10K	30 ATA L/R
20 L/R	20K	20 ATA L/R
30 L/R	30K	10 ATA L/R
40 L/R	40K	0 ATA
50 L/R	50K	10 ATA L/R

It is named “Rule of 40” because ideally, when co-speed and co-altitude and at 10nm, to have 40,000ft of LS, ATA = TA (but opposite in sign) and both should be equal to 40.
The idea is simple: add the difference between the “goal TA” (40) and the current TA to the ATA in the opposite direction, in order to generate room for the turn.

In other terms, the DT is a hard manoeuvre that uses “Cut Away” or “Cut Into” depending on the TA, to generate a quantity of LS sufficient to enable the turn into the bandit’s 6 o’clock.

For example, with TA = 30, LS = 30,000 rather than 40k. Therefore, turning to have 10 ATA (towards the cold side, so away from the target), should generate enough room to allow the Conversion.

Another example, with TA = 10, LS = 10,000. The fighter needs to generate an additional 30,000 of LS by turning to place the target at 30 ATA cold.
Realistically, the Lateral Separation generated is about 25,000 ft, starting from 0 TA and coming nose-on at 5nm.

This procedure sets the maximum ATA to 40 to ensure that the bandit is constantly inside the radar scanned volume even if it begins to manoeuvre. In theory, the maximum generated LS can be greater by placing the bandit at the radar gimbal limits (~ ±65°). Although this is possible, it is also not advisable: if the targets turns, it can leave the volume scanned by the AWG-9.

Last Step: Counterturn

The gameplans described in Part IV end at the usual goal of 40k ft of LS at 10nm. The last step is the manoeuvre that places the fighter in the Rear Quarter (RQ / Stern) of the bandit: the Counterturn.
This manoeuvre is somewhat similar to the precedent Gameplans executed in BVR as it follows a number of Gates to guide the fighter into its final positioning.

Note: this part is quite concise, so I opted to quote the P-825/17 directly when appropriate, rather than summarizing an already on-point dissertation.

10nm Gate
At 10nm with 40k LS and 40TA, V_C should be approximately 530. The fighter turns to Pure Pursuit and, if the 40k of LS goal is met, it should roll out behind the bandit at a distance between 0.5 to 1.5 nm, In LAR for a SRM employment.
The closer the fighter is to the final position (bandit’s RQ), the harder the turn becomes.
5nm Gate
The fighter is still nose-on, TA increases as range decreases. At 5nm there should be approximately 60 TA and 500 V_C. The turn should be hard and nose-on.
4nm Gate
Same trend as at 5nm, but the TA should be close to 70 and V_C to 450.
3nm Gate
The manouevre continues with the fighter still nose-on. TA should be close to 80 and V_C to 400.
2nm, 90TA, 90 DTG Gate
The fighter is now crossing the perpendicular to the bandit (FFP ⊥ BFP), therefore TA = 90 and V_C close to 300. The turn becomes harder and the nose-on setup is unchanged.
1.5nm, 150TA Gate
Now the fighter is In LAR for SRM employment. If the contact is classified as hostile, the fighter should employ.
The fighter starts a counter-roll, exiting the hard turn towards wing-level.
1nm, Wing Level, 180TA Gate
The fighter should be now at 6 o’clock of the target, at 1nm, plus 1,000ft of lookup (VD will be discussed later).
This is the ideal outcome of the intercept.

Note: Target Aspect and Slant Range are proportional.

The DDD on the left shows the fighter placing the bandit on collision (Gameplan for High TA; 35°-45°).
At 10 nm, the fighter turns to Pure Pursuit and the bandit is maintained at the centre of the radar scan volume until the completion of the manoeuvre.

Correcting the Counterturn

Matching the Gates described in the CT documentation is not always simple and when they are not closely followed there is a chance of overshooting. P-825/17 shows a table with relations between Range, TA and V_C and suggests committing it to memory. Be aware of the fact that such a table may not be applicable directly to the F-14 and DCS and that the aircraft speeds may change (doctrine assumes a co-speed intercept), resulting in a different V_C, especially at the entry point at 10nm.
Nevertheless, memorizing the trend is important, as it is important to converge to the suggested TA and V_C as the range decreases. At shorter ranges and high TA, in fact, Δ_V becomes relative.

Correcting the Counterturn

Counterturn assessment checklist

Quoting P-825/17, p9-3, fig. 9-1:

Essentially, the CT assessment can be boiled down to:

Assess Range and TA during the CT and compare it to the checkpoints;

Compare V_C to Range and check TA;

If V_C is higher than called for at range, the CT is hot;

If VC is lower than checkpoint at range, the CT is cold.

Example: VC is 450 kts at beyond 5 NM, the CT is COLD

The corrective action is to pull 20-30 degrees of lead;

“Lead him” to pilot;

Conversely, if approaching 5 NM and VC is much higher than 500 kts, the CT is HOT; “Lag him” to cool off.

Range	TA (Ideal)	V_C (Approximate)
10	40	580
7	50	530
5	60	500
4	70	450
3	80	400
2	90	300
1.5	150 (Fox-2)	150
1.0	180 (Ideal)	0

Counterturn: TA vs Vc plotted on a chart

The idea is to evaluate if the V_C matches the table above and Heat Up (be more aggressive, increasing the ATA) or Cool Off (induce drift to unload the closure, max 20ATA) if required.
The process is intuitive, to Heat Up the target should be place at 20-30 ATA Hot, therefore increasing the turn towards the target, switching temporary from Pure to Lead. Vice versa, to Cool Off, the correction is in the opposite direction (from Pure to Lag). The problem in both cases is to avoid overcorrections, especially when Cooling Off, or the risk is lagging too much behind the bandit.

The most important Gate at this stage is the 2nm, 90 DTG, quoting the P-825/17:

as meeting this goal means rolling out behind the target, In LAR for SRM employment;

the 300 V_C check reminds to remove the speed advantage;

this is the last occasion to turn from Pure pursuit to Lead, past this point the fighter cannot generate an energy sustaining turn rate sufficient to pull lead;

this is the final opportunity to use the geometry to solve range and VC issues; after this point, the intercept is a tail chase.

Point #3 is more related to the aircraft subject of the documentation (T-45 Goshawk). The F-14 is more performing in most circumstances, so it can still pull off hard turns although this is not the point: the point is following a procedure and orderly execute the CT to avoid distracting corrections and bleeding energy / overshooting, which can possibly expose the fighter to unnecessary risks.

Counterturn post Displacement Turn
If the Counterturn starts after a Displacement Turn, the initial setup (40k ft of LS) may not be as accurate. In this scenario, the Gates defined for the Counterturn can be used to monitor and adjust the manoeuvre.

Intercept Progression and Timeline

The intercept resulting in the stern conversion turn follows the same skeleton as the BVR Timeline (an accurate analysis of the Timeline is beyond the scope of this article, but it is planned so, for the moment, the older study will do).
The following is a short overview of the intercept progression and timeline.

Committing

The Picture is the first, pre-commit, step, it can be provided by the Controller post check-in or requested by the Leader.

Knight 1-1 [Aft] ► Darkstar, Knight 1-1, request picture
Darkstar ► Spectre 1-1, Darkstar, single group, Mary 11 22 33 thousand, tracking South, hostile.

Post-commit, after sanitization, commit criteria checked and the control switched to Tactical (Bullseye → BRAA), the section turns towards the bandit (Point and Assess).

Notes: both tactical control and Point and Assess help the RIO to evaluate the Geometry as ATA = 0, so TA = BR → FH, as discussed previously. During the intercept, the RIO can use the accurate information from the controller to almost instantly calculate the TA by using BR → BB.

Correlation and Declaration are fundamental to ensure that the section is “looking” at the correct Group, on top of verifying the ROE and the current declaration of the Group and the labelling.

Then the geometry is analysed, TA and LS are calculated and the Gameplan defined.

Recognizing the 40k LS Goal

Once the gameplan is set and whilst being executed, the RIO must monitor and understand when 40,000ft of Lateral Separation are achieved.
The gates mentioned in Part IV of the Intercept Geometry can be used as reference:

To capture the 40k LS goal, follow one of the following options:

the fighter turns to zero-cut (BR) after building 40k LS;
the fighter turns to zero-cut (BR) and maintains 40k LS to 10nm;
the fighter continues to reduce LS to 40k by means of collision (40 TA) until 10nm.

TA and LS should be continually assessed and the RIO should act if the plan in place is not providing the expected results.

Displacement Turn

If the goal of 40,000ft of Lateral Separation at 10nm is not met, the crew can try to introduce or remove LS before the counterturn.
The five steps to accomplish the DT are:

Determine TA;
Determine Distance from the displacement range (10nm);
Determine the ATA necessary to generate LS (displacement point);
Command the pilot to turn to the assessed displacement heading;
Once displaced, monitor the ROC Gates (discussed above in this article). When the pilot is tally, he will continue the CT visually.

The comms suggested by the documentation to instruct the pilot are:

Knight 1-1 RIO [ICS] ► “Left/Right Hard, put him XX L/R”

Then, once within 10° of the displacement point:

Knight 1-1 RIO [ICS] ► “10 to go”

Note: The pilot of the F-14 can only estimate the angles, so the RIO may want to provide the final “Steady Up” heading. There are exceptions to this rule however, as the RIO can, for example, display the steering marker to Collision rather than having it pointing to Lead.

Stern Conversion Turn

If the manoeuvre has been completed correctly, the fighter should be now in the rear quarter (RQ) of the bandit with:

1,000 ft look up (if introduced);
0.5 to 1.5 nm of range;
STT;
Tally (preferred).

Complete Timeline

The following is the complete Timeline for the Stern Conversion Turn, from the P-825/17. The same considerations outlined during the study of the BVR Timeline are applicable to this Timeline: for example, the weapon systems are different, the aircraft have different performance and the avionics of the F-14 is much older than the one considered in that document. Nevertheless, it is a good tool to organize and structure the intercept.

Stern Conversion Turn Timeline – P-825/17 7-12 (US Navy)

Demo

This is a simple demo of an intercept I put together as I figured that seeing it done may help to understand the process better. I plan to make a longer and in-depth video at some point, similarly to what I did for the BVR Timeline.

The scenario in this case is simple and results in a non co-speed intercept of a bandit, with a stern conversion turn and SRM employment.

Note: This is the actual second take of the video (I tried to pilot with the keyboard in the first, but it was rubbish..). There are a couple of imprecisions, resulting in an intercept less smooth and close to the documentation than expected. Nevertheless, since a perfect, by-the-book procedure is just a matter of trial and error, a more realistic intercept with discrepancies caused by the older avionics and minor human errors (turn not hard enough and retarded by a few seconds) could be more productive as they show the impact on the final outcome (in this scenario a further Displacement Turn to remove the excess of LS should have been executed, but I considered that monitoring the DT whilst flying would have created a lot of confusion).

Progression

The scenario starts with the bandit almost on the nose, to simulate the Commit into Point and Assess;
TA is evaluated when the bandit is dead-on (DO) as TA = BR to FH = 25R;
Close to 30nm, the gameplan is assessed:
1. First turn to BR, to let the TA build;
2. Second turn to Collision, 40ATA Hot.
The second turn is executed too late (ATA = 40, rather than 36), on top of V_F14 > V_BANDIT, resulting in a collision with TA = 50R.
The Lateral Separation at 10nm with 50TA is 50,000 ft, 10k in excess that should have been corrected during the collision phase or with a DT.
The Conversion Turn into the bandit’s RQ happens as expected: initially easy, later harder; but the Δ_V must be taken into account to avoid overshooting;
The turn allows for a perfect ID of the bandit both visually and by means of the TCS (in the video I relied only on the TCS). In this scenario the bandit is classified as Hostile and SRM are employed.

Out of the doctrine

After such a long discussion about angles, ranges and Gates, the question of the applicability of such concepts directly to DCS arises. The P-825/17 in fact is an “entry-level” training document as it does not cover any advanced scenario. Moreover, the reference airframe is not a high-performance fighter jet such as the F-14 or the F/A-18 and, on top of that, the avionics of the F-14 we have is much older than the one considered in the documentation, forcing the RIO to compute more information than expected (for instance, calculating the TA).

At the end of the day, as per any discussion relative to the doctrine or real life documentation, take away with it what fits your way of enjoying the game. If you think that the modern gameplans require too much attention or effort, then you may find the next part of the Intercept Geometry discussion interesting, since it covers the same procedures but taken from a document 20 years old, hence closer to the avionics and the capabilities of the F-14 we have in DCS.