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The impossible turn

What should a pilot do if they suffer a complete loss of power on take-off? This scenario is many pilots’ worst nightmare. Height equates to safety, especially in a situation where the engine has failed, so an engine failure after take-off represents one of the most challenging hazards a pilot can face.

Conventional wisdom dictates that a pilot should never attempt a 180 degree turn in this situation. During a student pilot’s training, the instructor emphasises how important it is to pick a field (or clear area) straight ahead and turn no more than 30 degrees. This gives the pilot time to establish a safe landing attitude and assuming the pilot took-off with a headwind, the landing will occur at the slowest possible forward speed. This minimises the risk of harm to the occupants.

A turn through 180 degrees back to the runway is known as the impossible turn and has unfortunately resulted in many fatal accidents in the past. The impossible turn presents many challenges and a pilot who attempts to turn back must have a solid knowledge of their aircraft’s gliding performance and a lot of practice, though it should be said that it has been achieved before.

How much height would the aircraft lose in the turn?

Without a thorough knowledge of the aircraft’s glide performance, it is highly likely that the pilot will underestimate the amount of height required to complete the turn. Assuming an aircraft suffers an engine failure at 300ft agl it would be reasonable to assume that the pilot would be surprised, so a reasonable reaction time may be four seconds. If the pilot then chooses to turn back to the runway using a standard rate turn, it would take one minute to turn through 180 degrees. At a typical glide speed of 65kts, the radius of the turn would be 2,100ft so the aircraft would be 4,200ft to one side of the runway at completion of the turn. The pilot would need to turn through another 45 degrees to point towards the runway so the total change in direction is 225 degrees. The total time elapsed at this point would be 75 seconds plus the four second reaction time. If the aircraft is descending at 1,000fpm, it would have lost 1,316ft in the time it has taken to bring the aircraft around to the runway. This would put the aircraft 1,016ft below the runway.

The impossible turn is when a pilot attempts to turn back to the runway from which they departed after suffering a loss of power.

What else can go wrong?

In the above situation, the pilot may notice part way through the turn that they will not make it to the runway. Their instinct may be to increase the bank angle to tighten the turn and apply back pressure to maintain height. This is a recipe for disaster. The stall speed increases in a turn. In fact it increases by 41% in a 60° level turn. The application of back pressure causes the aircraft to decelerate and the angle of attack to increase. If the pilot stalls the aircraft at such a low height in a steep turn, a serious accident may result.

If the aircraft contacts the ground during the turn, cartwheeling may occur. And if a successful 180° turn is made, the pilot should also realise that they now face a downwind landing. The increased ground speed and associated increase in kinetic energy also raise the likelihood of serious injury if they are unable to make it back to the runway, or overshoot the runway.

If the pilot has sufficient height, sufficient skill, and the aircraft has good glide performance, the turn may be possible, but the manoeuvre should be explored fully with a flying instructor to ensure it is achievable and the pilot is competent at its execution. Generally speaking, it is far safer to land straight ahead or within 30°, with a lower ground speed and the aircraft completely under control.

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