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Note before reading further that I'm asking this question purely on theoretical grounds, though you are more than welcome to talk about practical aspects as well.

Now, my question. It's common knowledge amongst many pilots that turnbacks are one of the least safe methods of attempting to survive an engine failure in a single engine aircraft. However, is it actually possible at all to turnback an aircraft to return to the airport perimeter or the runway? How much of it is simply pilot error in executing a possible manoeuvre, as opposed to pilots thinking that they can pull something off that is just impossible, no matter what?

For the purposes of this question, we shall assume the following:

  • there is only one runway, so a reciprocal turn is required (we shall assume 210 degrees)
  • the aircraft has a flaps up stall speed at MTOW of 75 knots
  • the aircraft has a best glide ratio of 1:12 at 100 knots

Alternatively, if you have any other information that is more akin to a real aircraft, you can use that in lieu of this information.

Sources or an explanation as to why this it is or isn't impossible would be appreciated in your answers.

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This question is too general unless you include what altitude you're at when the engine fails, how many degrees you need to turn back to in order to line up with a runway (which could be a different one than you took off from), and how many feet you will lose in turning that far. –  mah Jan 9 at 11:49
    
@mah: well, if I knew exactly how much the aircraft would descend, then there'd be no point in asking, but does that help a bit? ;) –  Qantas 94 Heavy Jan 9 at 12:15
    
It certainly qualifies things better! I'm not comfortable with posting an actual answer on the matter (people's lives being on the table and whatnot). In a safety seminar though, I was taught that it's a good idea to take your aircraft to 1500', pull power and turn 180 to get an idea of how much AGL you lose and how far you have to travel to get lined up... if you're comfortable with that in your aircraft you should be able to apply safety padding and make a good decision about turn back (rare on takeoff, maybe never) or land straight ahead. –  mah Jan 9 at 12:37
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Anecdotal: When doing my PPL training in SoCal another trainee had an engine failure on takeoff, at roughly 400ft. The instructor took control and turned back and landed with a tailwind. So impossible: no. Recommended: Probably also no. I'd still opt for a safe patch in front than attempt a turnback! –  Jamiec Jan 9 at 12:45
    
Why do you say "210 degrees" is required? –  SSumner Mar 9 at 19:03

9 Answers 9

up vote 9 down vote accepted

Nobody mentioned the theory so far, so I'll try to fill in.

Disclaimer: The below calculations and estimates are based on what I know about the physics involved. I don't know whether they are actually mentioned in pilot operating handbook of any aircraft.

To successfully turn back, you after climbing at best climb rate, when the engine quits you push down, execute the turn at suitably slightly higher speed to maintain the angle of attack and glide back.

The rate of climb is thrust/weight minus lift/drag, the glide rate is just lift/drag.

Glide rate in the turn is higher by factor depending on the bank angle (coordinated turn; uncoordinated turn is always worse). Calculating best glide rate turn leads to bank angle should be around 45°, speed should be about 19% higher to maintain best glide angle of attack and about 41% higher rate of descent than in straight glide. According to the article linked in the other answer, flying at just above stall speed (which is also 19% higher than in straight flight) should be better due to tighter circle despite worse lift/drag ratio.

The radius, and thus length of the turn of course depends on speed. At 110 knots (true speed, not indicated) the turn will take about 1.4 nm, at 160 knots it will already be about 3 nm. At 60 knots it will only be 0.42 nm. Since you need to maintain indicated speed, the true speed will slightly increase with altitude.

So for the turn back to be possible the plane needs to have sufficient power to climb faster than it will descend in the glide and you have to be high enough to allow for the extra gliding distance (which due to higher rate of descent corresponds to even longer straight glide).

All or most planes will have sufficient thrust at sea level to climb faster than they descend in glide. But since thrust decreases with altitude and temperature, if your departure point is high or warm enough, it may no longer be the case.

Even if the thrust is sufficient, the distance between climb and glide profile starts at zero on lift-off and will only become sufficient to cover the extra miles in the turn above some altitude. The altitude depends on many factors mentioned above.

It's not reasonable to try it without knowing what altitude is needed for it at current conditions.

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It is "remotely feasible", you can watch this pilot story from AOPA about someone who did it. But, that doesn't mean that you or anyone else will be successful in attempting it because of the large number of variables that you mentioned. And one successful execution does not mean that it's a good idea in general.

One suggestion I've read several times is to try it yourself in the air: set the 'ground' at say 3000agl then try it out with whatever aircraft configurations you like and see what the results are. But even if you pull it off in those conditions, will you do it again in a real situation with the added stress and possibly additional weight (passengers, luggage) in the aircraft?

All in all, based on everything I've read and been told, it's called the impossible turn for a reason. My training anecdote from an instructor was a local pilot flying with his son who tried it, made the turn but stalled out, crashed on the runway, made it out of the aircraft but then had to watch his son burn to death in the wreckage. That sort of story makes a landing in a field or even a street seem very attractive, which was exactly my instructor's intention.

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There's a very good discussion of the "impossible turn" at the following link:

http://www.nar-associates.com/technical-flying/impossible/possible.html

It goes into an AIAA study using a flight simulator with new and experienced pilots and it shows that while it's technically feasible, pilots need to train for it and be very strict with their bank angle.

There's a lot of detail in the link that's hard to summarize, but the gist is that most untrained pilots fail and crash in a simulator, so unless you've practiced it, it's not worth trying.

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Probably one of the best comments in that link is: "The final element of CAAPP is Planning. Before you pull onto the runway and apply takeoff power you should have planned what you are going to do if the engine quits." Flying isn't about reacting to issues. It's about planning for them before they happen, in case they do. –  Shawn Jan 9 at 16:18

Interesting question, especially as I'm learning to fly just now.

My pre-flight abort briefing with the CFI is that if we lose power below 700ft AGL, we're going to land on a suitable field 20° off the nose (after pitching for best-glide speed, 68kts in our plane). However, above 700ft AGL, I'm being taught that we are going to pitch for best-glide and turn to the airport and land at "any available runway". The plane we're flying is C172S and we have never tried this at the airport, but in the air we did 360° turns with idle engine and 68 kts with only about ~300ft lost altitude. I was truly surprised about that.

I'm still uneasy about returning to the field, though.

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The reason that we are trained to simply not turn back is the same reason we memorize and drill the instant action items in emergency checklists. When the stuff hits the fan, you don't have time to think about all the possibilities of your actions. Your initial response time is critical to a successful outcome. Especially when you're already low and slow. And in an actual emergency situation, your chances of responding correctly are severely diminished if you have to think about what you're doing. You should KNOW what you'll do before it happens.

$V_1$ cuts in a multi-engine aircraft are a great example of making an instant decision that may seem counter-intuitive. If an engine stops before you hit $V_1$ speed, you abort. Otherwise, you know for a fact that once you reach $V_1$ speed, you will continue that takeoff, even if one of your engines fail. You'll deal with the emergency in the air, where it's safer and you have time to run the drill. Turning back to the airport falls into the same category. Turning back may seem attractive, but if you're still in takeoff phase, your chances of success are much smaller if you try a tight bank in a slow, low aircraft.

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The answer is yes and no. If at a sufficient altitude, a return to the airport is feasible. If a suitable landing spot is in front of you that is the best option. You MUST know your aircrafts limitations and your skill level to determine when it is safe to return to the airport.

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Welcome to aviation! I think you meant to say "If at a sufficient altitude..."? Any more specific details you can give about how to determine how much altitude is required would be great, although your overall point about limitations is certainly correct. –  Pondlife Jan 9 at 19:53
    
@Pondlife - A safe altitude would be individual to the plane you are flying and the conditions you are flying in. There's really no hard and fast rule. That's why the "land ahead" guideline exists. Too often, what happens is that the pilot will panic and try to bank the aircraft around in a situation where it's already nose-high and losing airspeed. That's a very quick way to demonstrate the stall/spin recovery methods that I talked about in the other post. :-| –  Shawn Jan 9 at 23:31

It is not only remotely feasible it is very possible. One of our club members departed a sea-level airport and reached 6,500 feet altituce when the engine quit. He turned back and landed on the runway he departed from. He actually landed long and over-ran the runway.

Now try that at 500 feet above runway altitude and you won't be able to make it.

So where you are when the fan stops is important, as is your skill level. Get with a CFI and practice this!

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Your CFI should definitely be going over this in training. My guideline was always along the lines of if you are in the takeoff phase (low and still in the pattern) it's easy: don't try to turn back. If you're in the departure phase (climbing out of the pattern) then lower the nose, first and foremost, and make the decision. The important thing is to FLY THE AIRPLANE. –  Shawn Jan 10 at 18:10
    
That said, I've never had a full power loss on takeoff. I have had a partial power loss on takeoff as I was climbing out. I didn't have enough power to keep climbing without getting very slow, but I wasn't losing altitude when level. I was high enough to clear the trees, so I announced what I was doing over the radio and circled around the pattern at a couple of hundred feet. Made a semi-normal landing and taxied straight to the maintenance hangar. It wasn't much fun. –  Shawn Jan 10 at 18:17

I saw a Rallye perform a successful turn back at Bembridge. Probably preferable to ditching. I still wouldn't try it.

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Hi, welcome to Aviation. You might want to expand on the circumstances of this event, as currently this is more of a comment. How to Answer provides useful tips on how to make sure your answer is useful and helpful, which will help your chances of getting upvoted (and consequently increasing your reputation). Thank you and good luck! –  Qantas 94 Heavy Jan 11 at 5:51

Apart from the actual physical feasibility discussed in other answers the main risk is a stall situation during the turn.

Winch-launching of gliders is a situation where "power loss" in form of a rope-break is quite common and the reaction to this situation is one of the most importand drills during your training.

Apart from the initial speed and AoA recovery, the decision to turn or not is rather crucial, but when turning you have to take utter care of your speed to avoid stalling. This may be even worse for motor pilots, because you might want to keep banking with a "normal" horizon reference as usual, which can be a bad idea if you are lacking the necessary power to sustain that.

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