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It has been said many times not to do the imposible turn(180) after takeoff since almost always it ends in a fatal crash.

My question is, if you are flying a Cesnna 172, or any single for that matter, and you lose the engine right after takeoff but in front of you there is a high density city(houses, cars, power lines, trees, people walking, etc), should you still avoid the imposible turn or this would be a valid case to do the imposible turn?

Or is there some other case where the impossible turn would be valid?

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    $\begingroup$ For several months in 2023, Charlie Precourt's column in EAA's magazine "Sport Avation" exhaustively covered when to 180 back to the runway, for a range of airplanes. $\endgroup$
    – Camille Goudeseune
    Commented Apr 11 at 16:32
  • $\begingroup$ can you briefly mention any of those? $\endgroup$
    – Gabe
    Commented Apr 11 at 17:04
  • $\begingroup$ I'll let another EAA member summarize those columns into an answer. The summary of summaries: simulate the 180-to-touchdown at safe altitude, including 8 seconds of startled inactivity between power loss and maneuver start. Afterwards, from your GPS track measure how much height you lost and ground you covered. Remeasure with max weight, CG at limits, different winds, etc. Record those numbers for reference. $\endgroup$
    – Camille Goudeseune
    Commented Apr 11 at 19:54
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    $\begingroup$ Doesn't matter if what's ahead of you looks grim. If you don't have the energy for the impossible turn, you're writing checks your energy can't cash. Since this is already poor energy awareness, it's likely more will follow with asking the wings to do what they cannot and stalling it. $\endgroup$
    – Harper - Reinstate Monica
    Commented Apr 12 at 16:39
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    $\begingroup$ You can't do it, by definition, since it is impossible. You can try it... $\endgroup$
    – Dave Gremlin
    Commented Apr 12 at 23:14

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Generally crashing into inhospitable terrain while under control is preferable to a vertical spin into the ground short of flat terrain, which guarantees a bad result.

In any case, it usually isn't necessary to turn around back to the runway, which requires more than a 180⁰ turn since the maneuver is more of a question mark pattern. It's a matter of maneuvering to a survivable surface. "Land straight ahead" no matter what is just as foolish, if landing straight ahead takes you into an oil refinery, as trying to return to the runway from 300 ft. As the old saying goes, the rules and conventions aren't a suicide pact. It comes down to some judgement on maneuvering room from the point of failure.

It's better to forget about the concept of the "impossible turn, yes/no" and think in terms of "how much maneuvering margin does this altitude give me". To make that kind of judgement instantly, it means you need to know your airplane and its gliding ability and your own skill level. An airplane with a good L/D has way more options that a draggy biplane. Taken to an extreme, a 40:1 sailplane can have a tow line break at 300-400 ft and fly a complete pattern/circuit to land at the original starting point.

In general an airplane like a 172, with an L/D of around 9, will need more than 400ft to be able to turn and maneuver all the way back to the runway, if flown expertly and optimally. Go to a safe altitude and try it, and practice it and see for yourself.

But who says you need to reverse direction? There may be a golf course or a highway 90⁰ off the course that can be reached from 200-300 ft.

These eventualities should be part of the pre-flight planning from a particular airport. You brief yourself: If the engine quits at point X at 300 ft, where can I go? Make a few "advance decisions" so if it actually happens, you just react and put it down under control, even if it's trees (even there; if there are tall deciduous trees and a patch of short conifers, put it into the conifers, which will absorb energy like a big hair brush) .

This is part of the normal pre-takeoff checks in gliding, knowns as "Options" at the end of the pre-takeoff CISTERSC Nemonic. You observe the winds, review the terrain, and decide in advance what to do if a rope breaks at less than 400 ft.

I just had a fun and enlightening experience in my towplane checkout recently. We were doing circuits in the tug (a Citabria) and, mindful of some recent turn-back crashes, my check pilot eased the power back somewhere between 300-400 ft, catching me by surprise. After the quick run-through checking switches, carb heat etc, and pitching to maintain speed, I looked down, then back toward the airport, and instantly realized there was no way I could make it back. I pointed to a field about 45 deg off to the left and said "I'm putting it down there". He said "Good boy! Power's yours again".

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    $\begingroup$ These eventualities should be part of the pre-flight planning from a particular airport I would imagine this is a critcal part of being a pilot right!! Great explanation $\endgroup$
    – Fattie
    Commented Apr 12 at 17:33
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    $\begingroup$ TY. To the extent you can know the terrain beyond the airport. So much easier these days with Google Earth. It's actually kind of shocking that something very basic to glider training is rarely done with power. $\endgroup$
    – John K
    Commented Apr 13 at 0:59
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For the sake of simplicity let's assume that the impossible turn in this case is in fact fully impossible, so no borderline cases are considered. The actual choice in this case would be "where do I crash" and certainly there are circumstances where you preferably crash at the airport, such as the said airport being embedded in extremely densely populated area being one.

I used to fly from an airfield that can be considered as of the aforementioned type. However altruistic it may seem to prepare to crash away from populated areas, the take off briefing was always "in case of engine problems fly straight ahead and find a place to land", while knowing very well there were next to none.

So, is the impossible turn ever a valid choice, yes, but applicable in real life, perhaps not so much.

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