Intercept Geometry – Part I: Introduction

Intercept Geometry: Table of Contents

Looking Back before Leaping Forward

This is the last series of articles about Air to Air employment, at least for the moment. It has been a long journey, started a year and a half ago with the deep-dive into the F-14 avionics then the Timeline, with a glance at the transition into WVR (later I will conclude that series with the basic concepts of BFM from the point of view of the Radar Intercept Officer).

I used a bottom-up rather than a top-down approach for a number of reasons. The most important are:

  • knowledge progression: rather than introduce the Intercept and then open wide parenthesis to discuss the many topics, starting instead from the avionics and then move up to the procedures gives more tangible and immediate results;
  • pragmatism: consider the Timeline for example. From the targeting down to the merge, it can be used in any environment, even less simulative ones, as a means of coordinating and structuring an engagement. A complete intercept instead? It is definitely more limited and may require a more simplified approach.

The time spent on the corollary topics, such as how the avionics work and the meaning of the information displayed, makes the Intercept Geometry a much simpler topic to understand and put into practice.

Out of curiosity, I counted the words used in the articles covering concepts strictly related to the Intercept Geometry. The total, excluding this article and this series, is over 17,000. It has indeed been a long journey.

Intercept Geometry: Reference Documentation and Resources

Some resources I used:

  • The familiar CNATRA P-825, rev 02-2017. This is a fairly recent review of the P-825. The drawback is that it uses several “toys” not present in our old F-14A/B (and F-4, as I fully intend to port as much as possible to this majestic aircraft).
  • Strike Fighter Intercept, id est CNATRA P-825 rev. 05-2002. This older version is much closer, in terms of directly applicable procedures, to our favourite aircraft.
  • Syllabi of F-4 Phantom II, F-8 Crusader and other aircraft: declassified documents, sometimes unfortunately incomplete but incredible interesting and useful to understand the evolution of the doctrine through the decades. The “make it work with what you have” approach of those syllabi helps to better understand aspects of the geometry often not considered when a computer is doing most of the job.
  • Several papers and publications: on the internet a plethora of documents and studies are available to the public, such as discussions about the decisional process or material for air intercept training.

The Big Gap

Most of the declassified sources are basic training / IQT level, so they cover the basics and the simplest scenarios (id est co-speed, co-altitude intercept) for the most part, whereas in DCS this is hardly the case. On top of that, older techniques, such as the Beam intercept, are not covered either (although for different reasons). For completeness’ sake, I tried to include some paragraphs about those cases, on top of an overview of the most complex scenarios.

Related Articles

Definitions and concepts related to the Intercept Geometry are spread all over this website. I plan to mention them as they are discussed in this series but if you want to have a head-start, the following are some articles related to the Intercept Geometry:

  1. TID Part I: Ground Stab mode;
  2. TID Part II: Aircraft Stab mode;
  3. BVR Part I: Sanitization and Radar Mating;
  4. BVR Part II: Timeline Overview;
  5. BVR Part III: Timeline in Detail;
  6. BVR Part IV: Crew Comms;
  7. BVR, WVR & Intercept: Recurring Concepts (TA, ATA, Drift, Collision);
  8. Closure and Collision: TID “Hot” and “Cold” Sides;
  9. F-14 WVR Part I – From Beyond to Within;
  10. Determining Target Aspect: the BDHI.


As I often say, these articles are the product of my personal study of the sources mentioned above and the thorough testing of such concepts in DCS. As the documentation is freely available I doubt it is what actual front-line pilots use (besides the fact that is often outdated). Nevertheless, they are great sources of knowledge and allow us to better understand and organize that massive, confusing mess called Air Combat.

The Intercept

What is an air-to-air intercept? In the words of the P-825, is “a relative motion problem in which the weapons officer is constantly striving to control the position of the fighter in relation to the bogey aircraft.“.

If the BVR Timeline provides an organic temporal structure to the employment, the Geometry provides the spatial organization, the “how to get there”, aiming to gain a positional advantage. This is a fundamental yet often neglected aspect: new players especially have the tendency of placing a target dead-on and rush into it, without considering the next step, and the advantages of the superior positioning. Something as simple as a collision course in fact, can dramatically increase the chances of killing the target, as we have seen already in the article about the Simplified Intercept.

As for the BVR timeline, no matter the simulative level you prefer, there is always something useful to learn. A more arcade-ish environment can benefit by the better understanding of the importance of positioning. In a simulative environment instead, by for example learning more efficient techniques to execute a VID maintaining the positional advantage and following the ROE and, generally speaking, a more structured and organized engagement.


The typical and simplest intercept flows into a conversion towards the rear of the bogey with the goals of performing a VID and being in LAR for a missile employment. This intercept can easily become more complex by introducing a difference in altitude (Vertical Separation or Vertical Displacement) and can be useful even in other scenarios, for example rejoining a tanker. Naturally, if the goal is moving behind the bogey, the bogey itself should be unaware (for instance it does not have a RWR) but usually it is because the contact, at that moment in time, does not constitute a threat.

The BVR Timeline instead has the specific purpose of structuring the engagement of the hostile target, even multiple times if necessary. Why is the Geometry useful in this case? As mentioned, something as simple as the Collision Course in place of a Pure Pursuit can already dramatically increase the efficiency of almost any missile but the bar can be raised even higher, helping the crew to efficiently manoeuvre the aircraft in an a position that improves even further the PK of the missiles whilst increasing the survivability of the aircraft (imagine the effects of the crank but on a greater scale).

The Good Old Goal: Superior Situation Awareness

The intercept is often presented as a simple “fly for a certain LS and go pure“. Although it may work, this approach does not get even close to explain what happens under the hood and does not provide the RIO the tools to deal with an unexpected situation. Understanding the relations between Target Aspect, Slant Range, Antenna Train Angle, Cut, Heading Cross Angle and so on, drastically improve the Situation Awareness of the crew so, when an unexpected situation arises, the RIO has the ability to promptly interpret the information from the avionics and the AIC and deal with the situation or, in the worst case, recognize immediately the danger and turn cold.

Unfortunately, providing the notions required is not an easy task due to the lack of declassified advanced documentation, but I hope that in these articles you can find something useful and new to apply in the virtual skyes of DCS.

Topics Discussed in this Series

After a lengthy overview of the definitions, the discussion moves to the Intercept Progression. Constructs such as the LS Gameplans are introduced and the familiar BVR Timeline is updated in light of the new concepts, as the Timeline discussed here almost one year ago was extrapolated from its natural container (the geometry) to create a new, independent, tool.

As the progression changes depending on the objectives and the scenario (e.g. forward-quarter employment rather than horizontal stern conversion turn), the focus shifts towards the different approaches, and eventually all is linked together into concrete examples. The goal, as mentioned, is explaining these concepts in a simple way and provide ideas and suggestions.
Eventually, depending on how you enjoy the game, you can take from this what works for you.

Summary Preview

Note: this summary is not set in stone, and it will be updated as I progress into the documentation: some topics may eventually be grouped together in a single article or, vice versa, split into multiple parts.

This is a brief summary of the chapters composing this series about the Intercept Geometry:

Part I: Introduction;
Part II: Definitions;
Part III: Target Aspect and Lateral Separation;
Part IV-VI: Evolution of Gameplans: from the Korean War to 2020;
Part VII-IX: Practical application, BVR Timeline updated, reference gameplans for Shaw’s intercepts*.

*Note: Robert L. Shaw in his well-known book Fighter Combat: Tactics and Manoeuvring, covers a number of intercept techniques. I am still wondering if going through such procedures, defining gates and gameplans is worth or not. Feel free to give me some suggestions and pros and cons of covering those!

Covering doctrine and material from the 50s and the 60s is probably unexpected. There is a reasoning behind it:

  • In primis, because DCS is a sandbox. My favourite aircraft and role at the moment is the RIO in the F-14 A/B, flying in a setting that goes from the early 70s to the late 80s; therefore a period when automation and computers were not as predominant as they became in more recent years (the dream would be flying the F-4E or F-4J and the recent announcement from ED really broke my heart 😦 );
  • Next, because each aircraft have different avionics. The procedures used on a MFD of a modern F/A-18C cannot be ported 1:1 to an aircraft half a century older such as the F-14;
  • Lastly, simple curiosity. On top of the fact that procedures specific to an aircraft can benefit by the influence of more advanced or modern procedures.

That’s all for this introduction. Part II should be available soon. Stay tuned!


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