Almost every pilot’s nightmare is practising an aircraft forced landing.

Even more so, a real forced landing. To complicate things further, there are a few alternative landing techniques a pilot may be instructed to follow.

Even though at Learn to Fly flight instructors offer impeccable pre-flight briefings and guidance throughout the flight, the prospect of undertaking this practice run is still enough to make anyone feel at least a little bit nervous.

If you, like me, find the technique involved with aircraft forced landings to be super fascinating, then I urge you to continue reading as I unpack traditional and alternative approaches.


A fundamental flaw in the traditional High/Low Key technique has been commonly taught in most civilian flying schools across the world. This technique depends on your judgement of the trajectory of the flight in order to somehow nail 1500 feet by your low key position, which is normally abeam your IAP (Initial Aiming Point) on a downwind.

highlow key technique

As a matter of fact, there are too many factors to process in order to clearly judge the altitude of our aircraft in a glide at a particular arbitrary point. It also requires the pilot to be extremely knowledgeable about surrounding terrains and the elevation of the terrain they are flying over, which sometimes can be challenging.


The Royal Air Force has developed a new Constant Aspect technique in order to combat the issues of different aircraft and the requirements for some undetermined judgements.

The principle of such aircraft forced landing technique is that it removes all the guessing of altitude and descent angle. It narrows down to one thing, which is called the “SightLine Angle” (SLA). It is the perceived angle between the IAP of your landing field and the horizon. Realistically, all you can look at during the forced landing with this technique is ONLY airspeed and the SLA.

sight line angle 1

The SLA is the “Aspect” which is part of this entire forced landing approach, and the “Constant” is basically the entire technique itself. The ultimate goal of the entire pattern is to keep your SLA constant as you approach the IAP.


The first step to fly this approach is to pick a landing field within safe gliding distance and meet the criteria set out by your instructor. Next, you can choose a sensible IAP within the first third of your landing field. This will be the “fulcrum” where your aircraft will pivot during the entire pattern, which ideally is a round pattern unlike the High/Low Key method with a rectangular pattern.

constant aspect technique

Ideally, you will join what is equivalent to a crosswind. However, depending on wind direction, it may be a direct downwind or a midfielder crosswind join into the “circuit”. It is important that your bank angle does not exceed 20 degrees during the approach. Otherwise, you may risk the SLA either increasing or losing airspeed and glide ratio due to the reduced vertical component of lift and increased drag.

If your SLA is increasing (getting too high): Deviate from best glide speed or increase spacing. If your SLA is decreasing (getting too low): decrease spacing, fly inwards.

When approaching final, you must make the turn in to directly approach your IAP. This is the time when you decide, using your knowledge of the trend of your SLA, whether you;

  • cut in short
  • fly a standard final
  • or overshoot and then turn back onto final depending on your height.

If the SLA is high, you have three options to get back onto glide path. You can use flaps, do S-turns or do a steep slip, or you can combine S-turns and steep slips if it is ridiculously high.


This technique is not only used by RAF but also being slowly accepted by flying schools around Europe and the UK.

It is recommended that everyone should practice the entire pattern all the way down into the flare and touchdown. You will find out, if you really are ridiculously high, you can still hold the slip into the flare, centralise the rudder when the aircraft sinks, and then continue to flare.

For more information about our flight training, head to our courses page.

Contributed by Learn to Fly student Howard Lau.