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)
- The “Unknown Procedures” are guidelines to follow in case the fighter lacks info or has poor SA (such as no radar contact).
- The Fleet Conversion Procedures are applied when the CC is dropped and the goal switches to a FQ missile employment.
The topics presented in this and the next part of the Intercept Geometry study are hardly applicable to DCS directly. However, they all have something to teach or show, such as a different approach to a scenario, how different concepts and agencies are linked together or provide a quick look at how to deal with a non-cooperative target.
In some cases, the similarities with the procedures used 20 years later are very noticeable.
Usually, the intercept starts from the Bullseye call from the Controller: it can be vague (e.g. cardinal point from the Bullseye) or precise (e.g. magnetic bearing from the Bullseye). No matter the level of detail, it should be enough for the fighter to point its sensors towards the indicated area and spot the bogey.
Post commit, the true correlation comes when the fighter acquires and gives contact call with precise digital Bullseye or BRA format. If satisfied, the Controller can then provide declaration information.
In real life, especially as we move backwards in terms of technology and procedures, this is not always the case and the information provided may be incomplete. The “Unknown Procedures” cover how to perform an intercept when the BH is unknown (due jamming and electronic countermeasures, for example).
Unknown Intercept Procedures
The documentation describes the procedures as:
“[…] an exercise in drift control, scope interpretation, and target aspect analysis.”
By the end of this short discussion you will probably agree with this definition!
The principles on which the procedures are based on are:
- CB = ½ Cut, in co-speed scenario;
- a bogey on collision will not drift;
- if a bogey is not on collision it will drift away at a predictable rate, based on range and degrees off the CB;
- as the range decreases, the degrees a bogey is off CB and the drift both increase.
Unknown Procedures Workflow
- Starting point: Unknown
The first step is determining the initial fighter heading when the bogey is on the nose, based on the AIC/GCI information. If the target is passed via Bullseye reference, then the fighter should roughly correlate, find the target with the radar and place it on the nose.
Once Steady Up with the bandit on the nose, the FH is unchanged until post step #2.
- Drift Analysis
Emphasis is put on the most important factor of this type of intercept: the DOP (Direction of Passage), since it is the basic information needed to perform a reattack.
Once the fighter is wings level, the RIO analyses the drift for 2-4 nm. If the target drifts right, then there is Right TA and the DOP is left-to-right and vice versa. If there is no drift, the TA is close to zero and the fighter should maintain the heading.Drift Analysis from GCI, Determining DOP
If at 25nm no radar contact is established, the fighter can request to switch to BRA (“Go Tactical” or “Go BRA for <own callsign>”). The controller should call the drift according to his radar scope, this allows to calculate the DOP. If the drift on the scope (when steady) is discordant with the GCI, make corrections according to the radar scope.
- Countering the Drift
Countering the drift is the next step of the analysis. Determine the DOP, then turn into the drift to counter it and place the bogey on the 30° opposite the direction of drift (e.g. right drift goes to 30L ATA). Wait for the next drift assessment.
- Estimating Cut, TA and BH
These parameters are estimated after displacing the bogey to 30ATA, making a BRA call and assuming the bogey is on CB. Since the Cut is 2 * ATA (remember that when co-speed, CB = Cut / 2), is now easy to estimate BH (useful if contact is lost during the CT).
These are estimates and require confirmation (i.e. no subsequent drift).
- Reanalyse Drift and Make Further CCC’s
The drift is monitored until no drift is observed (Remember that any drift = no CB):
- Inward drift (→ fighter’s nose) = actual TA > estimated. Counter by displacing outwards 20°;
- Outward drift (← fighter’s nose) = actual TA < estimated. Counter by displacing inwards 10°.
The reason why CounterIN > CounterOUT is simple: ensure that the TA does not get too large ( > 45TA), so that an AIM-7 shot is not lost.
Whenever possible the RIO should try to determine the BH by, once steady HDG, rounding the FH to the closest 10°. Then add or subtract the Cut that is now assumed to determine the estimated BR. From the BR, the BH is immediate. The initial estimation may be off by a lot but following estimations should be more precise and the error should be within 20°.
Example I: No radar contact for Initial / Secondary Corrections
The following example is taken “as it is” from the P-825/02, p 124.
- The fighter, Sweep, has steadied-up on a heading of 340° after the initial GCI call of
“Gritrock, picture, single group, Bull 220-42, medium, flank east.“
- Once steady, the fighter does not have radar contact after the next GCI call and therefore commands “Gritrock go tactical for Sweep“. GCI responds with “Sweep, Gritrock, single group, BRA 326-24, medium“.
The fighter then turns to place the contact exactly on the nose (new fighter heading 326°).
- Once the fighter is steady, the next two calls are BRA 326-23 and BRA 327-22. After hearing right drift, the fighter classifies the DOP as left-to-right and counters the drift by commanding “Right hard” to place the magnetic bearing call at 30°L ATA (with a heading of 357).
- The fighter estimates a 60°L cut, 30°R TA. The weapons officer continues to analyse the drift for further corrections.
- The fighter has steadied on 357° after the initial correction.
- Subsequent GCI calls are “328° at 21 miles” (no reaction is made since this is the new starting point for subsequent drift analysis), and “329° at 20 miles“.
- Continuing to analyse the left to right drift, the weapons officer commands the fighter “Right hard” to counter the drift and place the magnetic bearing call at 50°L ATA. The turn is commenced immediately after observing any drift – drift is not quantified during secondary drift analysis.
- The fighter has steadied-up on 019° after the secondary correction.
- The weapons officer now estimates a 100L cut, 50°R TA, and BH 100°.
- The next bearing calls are “329° at 19 miles” and “328° at 17 miles.“
- After noting the outward drift, the weapons officer commands “Left hard” to place the bogey at 40°L ATA making the fighter’s heading 008°.
- The updated estimate is an 80°L cut, 40°R TA and BH 110°. Throughout the entire run, the OUI should be striving to gain contact through good search techniques.
Example II: Radar contact for Initial / Secondary Corrections
The following example is taken “as it is” from the P-825/02, p 125.
- Initial GCI call of “Gritrock, picture, single group, Bull 194-68, medium.” The fighter achieves radar contact in the turn and steadies with the contact on the nose at 237°.
- Radar contact at 29 nm, and the weapons officer analyses right-to-left drift (Scope interpretation is critical).
- Fighter commands “Left hard” to place the bogey at 30°R ATA (opposite of the direction of drift).
- The fighter has steadied 205° (due to continued bogey intercept drift in the turn) with the bogey at 30°R ATA.
- Initial estimate is 60°R cut, 30°L TA. The fighter makes a contact call, “Gritrock, Sweep, BRA 235-26, medium, declare“. GCI responds with “Sweep, Gritrock, BRA 235-26, hostile engage“.
- The contact is 33 right ATA, so the fighter commands “Easy right” to place the contact at 30 right ATA. At 23 nm, the fighter observes outward drift.
- Command “Right hard” to put the bogey at 20°R ATA and the new heading will be approximately 216°, though the angle off is more important than our exact heading.
- Updated estimate is 40°R cut, 20°L TA, and (rounding fighter heading to 220° and adding the 40 right cut to get a bogey recip of 260°) BH 080°.
- The fighter continues to counter the drift and update cut, TA, and BH estimates until no more corrections are required.
Large Target Aspect
If a correction places the bogey at 50ATA and inward drift is observed, then the TA > 50 and speed advantage must be used by the fighter to control the intercept.
Rate of Closure (VC)
High VC probably means low TA. You can verify your speed and compare it to the VC.
Unknown Procedures Chart
These charts are reported “as they are” and provide another means to visualize the procedure. Again, the purpose of this discussion is not learning to apply these procedures, rather understand how they work and which concepts are involved, to expand our understanding of the air combat in unusual and complex situations.
|Drift Direction||DOP||Move Bogey||Assume|
|Right||Left-to-Right||30°L ATA||60°L Cut|
|Left||Right-to-Left||30°R ATA||60°R Cut|
|10°||Inward||Increasing||30° ATA||60° Cut|
|20°||Inward||Increasing||40° ATA||80° Cut|
|Outward¹||Decreasing||10° ATA||20° Cut|
|30°||Inward||Increasing||50° ATA||100° Cut|
|Outward||Decreasing||20° ATA||40° Cut|
|40°||Inward||Increasing||50° ATA||100° Cut|
|Outward||Decreasing||30° ATA||60° Cut|
|50°||Inward||Increasing||50° ATA²||110° Cut (60° TA)|
|Outward||Decreasing||40° ATA||80° Cut|
|Outward||Decreasing||45° ATA||100° Cut (55°TA)|
¹ Inside 20 nm with 25º ATA or less and outward drift, bring bogey to nose to check DOP;
² Add buster.
Unknown Procedures: Conclusions
What can we take away from this very brief mention of the Unknown Procedures? Besides the “how cool is this” (or how boring, but if that’s the case, what are doing on this website? 😛 ), there are a few interesting points worth mentioning:
- The quote above, defining these procedures as “[…] an exercise in drift control, scope interpretation, and target aspect analysis.“, tells a lot about how those elements are connected, and personally, I have never seen it this way. For example, I never thought about using the BRA to estimate the drift and the DOP, both in terms of angles and rate, and use these information to correct more or less and start to take control of the intercept. I tend to be overly focus and to “tunnel-vision” on the TID and the DDD;
- If you have not noticed, the “Unknown Procedure” involve almost any skill in the RIO’s Book of Geometry. Not only that, but they show how a successful intercept is the result of the teamwork and collaboration between the RIO, the Pilot and the Controller
- Predictable and linked to the previous point, these procedures highlight once again how poor the current implementation of the AWACS is in DCS. A substantial overhaul is needed, especially if we’ll ever get the F-4 Phantom and similar aircraft
- My last observation is exquisitely procedural: point #5 and the inwards/outwards drift and relative corrections are very intriguing, if you manage to visualize the scenario. It is a situation I did not think about, and it is indeed a valuable procedure.
Fleet Conversion Procedures – Part I
Due to the length of this article I split this chapter in two sections (the documentation splits this chapter similarly). The first part covers the why and how; the second is very brief and mentions the case of a heading jinking bandit.
The Fleet Conversion procedures have been already discusses in some form in the previous parts of this series, so I will mention only some parts of them.
Let’s start by the definition of “conversion“:
The conversion is a long-range (30 nm) set-up where the bogey is taken off collision in order to manipulate the given TA.
Previously the goal was different, namely to place the bandit on a Collision Course to decrease range whilst maintaining the TA. These procedures instead allow the fighter to optimize the Target Aspect or the Lateral Separation for a particular situation.
The documentation provides a list of circumstances where TA or LS displacements are appropriate. The following is the complete list as it gives a good idea of the purpose of the Conversion procedures:
- Sun position, terrain, and other environmental considerations;
- Lack of one or the other type of missile;
- Section tactics and restrictions;
- Enemy tactics and formations;
- Position of home-base, a defended force, or the defended point;
- Requirement to visually identify the bogey.
This list immediately raises some interesting points. For example:
- Focus: be aware of the surroundings (i.e. terrain) implies not only maintaining good SA, but also avoiding the habit of going “tunnel-vision” on the display;
- Proactivity: use your knowledge to fulfil the task, not as a monolithic, rigid, checklist;
- Initiative and flexibility (e.g. lack of a missile): relying on only a type of ordnance (looking at you, 6/0/2!)
AIM-7 Sparrow Attack
Head-On / Advantages of Low TA
The AIM-7 Sparrow has the highest PK from Head-On (0° TA), which also allows for maximum range of the FOX-1. Moreover, no Lead turn is required but the lack of Lateral Separation along other factors may leave the fighter in a vulnerable position.
Forward Quarter / Disadvantages of High TA
When the TA is between 30° and 60°, the Lateral Separation is sufficient to enable a more effective Sidewinder reattack, but the PK of the AIM-7 is much lower.
Besides this aspect, other disadvantages can be noted:
- Lower VC → shorter RMAX;
- LC requires a larger turn;
- The Doppler differential between target and ground return is poor, so it can potentially be masked in the ground return;
- Greater TA and LS (→ poor position advantage) allows the bandit to penetrate much closer to the defended force;
- Chaff-type countermeasures by the bandit are more affective closer to the beam.
These considerations mean that, in a real-world situation:
[…] the fighter will most likely seek a low target aspect situation rather than accept whatever initial TA is presented. The knowledge of how to manipulate TA gives the fighter a flexible gameplan […]
The BFP is paralleled by an LS line representing the goal LS at lead. The bandit is pictured with a line radiating outwards representing the goal TA ( → the desired amount of TA at lead). The resulting representation can be broken down into four areas:
- I / II: insufficient TA, insufficient LS;
- III: sufficient LS, insufficient TA;
- IV: excessive TA and excessive LS.
At a glance this image is slightly confusing, until you realize is very similar to the following, although with different goal and purpose:
The four scenarios described above are dictated by the fact that the fighter can be anywhere on the bottom horizontal line (whereas in the modern discussion the fighter is already “on a side”), and therefore the amount of LS varies hugely depending on the scenario.
For more information about the Modern Gameplans discussion, based on the P-825/17, have a look here: Part IV: Modern Gameplans.
The calculation of the LS in this scenario is different from the usual formula as it is a prediction of the LS that the fighter will have at Lead range:
LS = TA * RNGLEAD
RNGLEAD is the Range at which Lead turn normally occurs. A couple of examples:
- TA = 10; Lead turn at 12 nm → LS = 12k;
- TA = 25; Lead turn at 10 nm → LS = 25k;
Also note that all TAs > 22 will equate to an LS that is equal to the TA.
Area I / II : Insufficient TA, insufficient LS
When the intercept is in Area I, the fighter wants TA on the opposite side from what is has at the start of the intercept.
Once the fighter crosses the BFP, the Area I problems turn into Area II problems. No matter where the fighter starts, the amount of LS in Area II is between 0° and the Goal. Therefore, since there is not enough LS or TA available, the fighter needs to Cut Away from the BFP, increasing the two. The Cut places the BB on the opposite side of the BR with respect to the FH.
Area III : Sufficient LS, insufficient TA
This scenario sees the fighter outside the goal LS line, but with insufficient TA to turn immediately to collision. The fighter should turn to 180° DTG heading ( = Zero Cut). This condition captures the LS but allows the Target Aspect to build.
The heading is maintained until the goal TA is satisfied, then the fighter should turn to attack heading, creating a collision intercept.
Area IV : Excessive LS, excessive TA
To solve this situation, the fighter has to turn generating a Cut Into greater than Collision, in the direction of the BFP.
After assessing the situation and determining TA and LS, the fighter employs techniques of TA manipulation very similar to the ones already discussed; using known relations such as:
- “as the range halves, the degrees off CB will double“
- on CC, “as the range halves, LS is reduced by half“
I don’t plan to cover those again, and if you are interested in the whole thing, I strongly recommend you to get a copy of the P-825/02.
Before wrapping it up, a brief review of the goals and the flow of these procedures:
- The objective is achieving an LS / TA goal, starting from 30nm, to enable a Fox-1 employment;
- The bandit is taken off CC to manipulate the TA;
- The picture is analysed and the gameplan is determined and the fighter rolls for the initial Cut;
- If the fighter is 1° off the desired goal, it has to perform a Reconversion. In other words, it has to rapidly react and manipulate the TA to satisfy the LS / TA goal.
- Post Fox-1 the fighter press on and displaces to enable a Fox-2 employment from the RQ.
Fleet Conversion (Part I): Conclusions
The Fleet Conversion procedures remind very much the moderns techniques for Lateral Separation and Target Aspect manipulation already discussed. The most glaring difference is that the 2017 documentation does not mention the Fox-1 employment, and it is entirely focused on the stern conversion turn. I guess that there are at least two reasons for that:
- The AIM-7 is being phased out (I haven’t found any reliable source, Wikipedia is vague, apparently it is still stocked but not in active use since 2018 – give me a shout if you find an official statement, please!);
- AIM-120 employment techniques are probably covered later in the doctrine, but not in the declassified, initial, documentation;
- As a sidenote, the Lead Collision intercept with AIM-7 Sparrow attach is still present in the P-825/08 (chapter 8) and it is still followed on by the AIM-9 employment.
That being said, these techniques are still critical as they help us to understand the factors that are involved in a missile employment and how the flow can evolve after the first employment (having a gameplan defined post “timeout” is critical!).
They are also still actual because in DCS, any time period or aircraft can be simulated: remember that the AIM-120 became operative quite recently (1991) and only after the major conflicts of the last century, and even after the end of the Cold War. This means that any F/A-18C and F-15C or other aircraft flying in any of those scenarios will be armed with AIM-9 and AIM-7.
As a final note, it would be interesting to understand if and how Lead Collision benefits the employment of AIM-120 and AIM-54: considering how powerful the rockets motor are compared to the AIM-7 and the fact that both can “loft” to extend their range, the impact is probably less pronounced, but I will try to answer the questions (for the Phoenix) as part of the new PK model once the mission guidance work is completed by Heatblur and Eagle Dynamics.