The Impossible Turn is the subject of the latest video in the Reality Check series from the Aircraft Owners and Pilots Association Air Safety Institute (ASI).
The debate about the “turnback” to the departure runway after engine failure on takeoff — known as the impossible turn — reemerged after the March 2021 crash of a Beechcraft Bonanza A36 in Pembroke Pines, Florida.
In Reality Check: The Runway Behind You, the AOPA Air Safety Institute tested the disputed maneuver using a Piper PA-18 Super Cub, a Van’s RV-4, a Cessna 172N, and a Beechcraft Bonanza A36.
“Our study was conducted by highly experienced and proficient pilots flying predetermined profiles in near-perfect conditions. We documented our findings, and the different results of turning back to the runway were surprising for each of us performing these flights,” said ASI SVP Richard McSpadden.
Since the publication of AC-83J, there has been a renewed interest in the turnback maneuver. As both an aerodynamicist and CFI for many years, I have followed the articles and blogs written on the turnback maneuver. A significant amount of the information on this subject is misleading and in some cases incorrect. After recently retiring from SpaceX, I decided to write a White Paper on the turnback maneuver This paper was based on a two-hour FAASTeam seminar I gave back in 2010. The title of the paper is “Single-Engine Failure After takeoff: The Anatomy of a Turnback Maneuver”. The paper uses basic aerodynamics (i.e. Chapter 5 of the Handbook of Aeronautical Knowledge, 8083-25B) to convey to the Pilot community how the various parameters influence the outcome of the turnback maneuver. In every article or blog on this subject, the author always starts the turnback scenario with the aircraft climbing out to a specified altitude and then experiencing the engine failure. To truly understand the turnback maneuver, one needs to put the cart before the horse. This means one needs to view the turnback maneuver in reverse. The first step is the ask the following question: If the turnback maneuver is initiated at a specified distance from the departure end of the runway (DER), how much altitude will be lost in returning to the runway? One can then make a simple plot of the altitude loss during the turnback maneuver versus distance from the DER. This part of the turnback is only a function of the gliding capability of the aircraft. Thus, one can compare the turnback properties of different aircraft with this simple plot. Step 2 is the steady climb phase of the turnback maneuver, which asks the following question: For a given established steady climb angle over the DER, how much altitude would the aircraft require over the DER to match the altitude loss in the turnback maneuver as a function of distance from the DER. One can then make a plot of the required height of the aircraft over the DER versus the distance from the DER. The final step corresponds to the takeoff and departure phase of the flight, which asks the question: For a given departure profile, how much runway length is required for the aircraft to reach the required height over the DER, as a function of distance from the DER. One can then make a plot of the Required Minimum Runway Length (RMRL) versus distance from the DER. The resultant plot of the RMRL versus distance from the DER is a tool that the Pilot can review on the ground, which lets the Pilot know when never to attempt a turnback maneuver. This allows the Pilot to decide on whether he/she will attempt a turnback maneuver before the takeoff roll begins. In addition, if the Pilot has decided he/she will execute a turnback maneuver if the engine fails on takeoff, there is still a no-go decision in the air, if the Pilot determines the aircraft is below the required height over the DER. In the paper, I show how one can generate the above 3 plots for a C-172.
Les,
Thanks for the comment. I did find your white paper dated 7/25/2020.
There is a lot of math to work through.
I’ll try to work the math for my C175, and fly some tests at altitude.
Jim,
If you need any clarification of the methodology or how to interpret the results, feel free to contact me.
Best Regards,
Les
lgtech@roadrunner.com
(818) 414-6890
Les,
Thanks. I’d like to do some flight tests , at low altitude; wings level glide,a nd then glide at best glide speed at 30 and 45 degrees bank.
I found a turn radius vs airspeed graph per, R= V*2/ 11.26 x tan [angle ].
The airports that I fly our of have 6,000 ft runways. but some others are 2,600 ft.
regards.
Jim,
Your formula for the turn radius is ok.
(1) In the case of the wings level glide, it is best to use a stabilized rate of decent at various KCAS around the best glide speed for the weight of the aircraft in the flight test. To back out the best glide angle you will need the TAS of the aircraft. One should perform the glide over an altitude change of 1000 feet, and average the TAS over the 1000 feet. Not sure of your equipment, but if you have a airspeed indicator with a TAS outer ring, you can use that with the OAT gauge. One can also utilize some simple techniques to get an estimate of the TAS if the winds are not light.
(2) In regard to the gliding turns, the paper shows there are four independent variables in the formula for the altitude loss per degree of turn. These are weight, air density, angle-of-attack, and bank angle, If one is attempting to find the optimum bank angle to minimize the altitude loss per degree of turn, it is necessary to keep the other 3 variable the same in the flight experiment. Thus, if the aircraft initiates the gliding turn at the same altitude with the aircraft weight almost the same, then it is necessary to keep the angle-of-attack constant while varying the bank angle. Typically one determines the accelerated stall speed for the given weight of the aircraft and then adds a safety factor of 5-10%. For example, if you are comparing the altitude loss per degree of turn at 20 and 45 degrees, the ratio of the speed would be square root of the load factors, i.e., square root [Cos(20)/Cos(45)], which is 1.33. It is important to be sure the airspeeds you use are corrected for the actual weight of the aircraft, since the stall tables are usually for gross weight.
Give me a call at (818) 414-6890 is you require any clarification of the flight test.
Les
Les, Thanks for the info on the flight tests.
It will be in the 100’s here in Northern CA, so my tests will wait for cooler weather…like 80 -90.
My C175 should perform the glides similar to the C172 that you used in the text.
Thanks again,
I’ll advise of my results and if I need more assistance in doing this correctly.
Jim Hughes
EAA 1541, Lincoln, CA ; khlm
Jim,
Correction on the 1.33 factor in my previous reply to you. It should be sqrt(1.33)=1.15
So airspeed ratio between 20 degree bank angle and 45 degree bank angle should be 1.15 in order to keep angle-of-attack the same in the flight experiment.
Les
Real world event, barring altitude being well defined as high enough or too low, it’s nothing more than a guess on game day.
Why is a successful turn defined by reaching the runway and thus necessitating a270 turn? merely turning 180 and getting to land anywhere at the airport ( a large wide flat area devoid of power lines, school buses full of children and buildings) is much more favorable than off field.
Since the publication of of AC-83J, the subject of the turnback maneuver has reared it head again. There are many comments put forth by the Pilot community including CFI’s on this subject.
It is unfortunate that there is a lot of misinformation about the aerodynamics of the turnback maneuver that is proliferated on the internet. As an Aerodynamicist for over 50 years, and a long time flight instructor, I decided to write a White Paper on the Turnback maneuver in order to help educate the Pilot community on this subject. The paper uses a C-172 as an example of under what conditions a Potentially Successful Turnback Maneuver (PSTM) is possible. It also compares the Schiff rule-of-thumb with the aerodynamic model of the C-172, and shows the Schiff model does not properly represent the turnback maneuver since it is overly conservative in that it dismisses PSTM’s closer to the departure end of the runway (DER). If you are interested in receiving a copy of this paper, go to aviationmobileapps.com/blog. If you are an EAA member you can also find it on the website
https://www.eaa.org/-/media/Files/EAA/EducationResources/SportAviation/2020-12-14-Turnback-Maneuver-Anatomy.ashx
Engine out on takeoff? Consider the following:
Think airplane, not automobile. It’s a 3 dimensional problem, not 2 dimensional one.
Physics tells me I have put enough potential and kinetic energy into the aircraft to get back to the runway. It’s all in how I use that energy.
We all have seen the solution at an airshow where a pilot makes a low pass over the runway, pulls steeply up, climbs, swaps ends, and swoops down for another low pass in the opposite direction. Recall that Bob Hoover routinely did it, engines out.
That’s the way I was taught from day one. My instructor had a low opinion of any kind of gliding turn after an engine out on takeoff.
Understand this. The AOPA tests, as well-conducted and well-meaning as they were, failed to use the optimal return profiles. Their results were compromised by the inefficiency.
The best steady state turn-back in a lightly-loaded C-172 is about sixty-three degrees, with an angle of declination of around twenty-four degrees. If properly flown, that scenario would have greatly improved the success of the final glide.
I might add this. Departing the airport on the runway centerline is also a mistake. A much better alternative is accomplished by drifting in the climb to the downwind side. This allows the pilot to perform the turn back from abeam.
Positioning the aircraft so eliminates the need to turn much more than one-hundred and eighty degrees. That in turn saves potential energy, allowing a better final glide. Even better profiles can be found than in the steady state.
I hesitate to discuss them, because I already draw fire for suggesting it is alright to turn tighter than forty-five degrees. But my purposeful intent is twofold; to further the discussion away from impossible and move it towards mostly possible.
And second, to promote instruction in the methods which give the proficient pilot best odds at a safe return strategy. Whether those options are employed is always, as they should be, at the discretion of the pilot in command.
If you are the only one in the sky and there are no obstacles, I guess drifting to the downwind side in a crosswind isn’t going to hurt anything. But realistically, other pilots except departures to track the centerline and drifting downwind could result in dangerously close distances to other traffic on either the downwind or upwind legs. And where I’m based, it would drift you toward a nearby tower 1800ft above the runway.
expect departures
Yes, we all should track the extended centerline…it’s what all others expect.
It would be a good idea to remember to turn into any crosswind, which would reduce the turn radius.
Flying Mag had a recent article on how rare an engine failure on takeoff is.
https://www.flyingmag.com/story/pilot-proficiency/minimizing-takeoff-risks/?utm_source=internal&utm_medium=email&tp=i-1NGB-Et-V4q-1KD6MG-1c-NI5Y-1c-1KD2zR-l69rGm1yLN-ElS6R
“The debate about the “turnback” to the departure runway after engine failure on takeoff — known as the impossible turn….” Hhmmmmm.
So what were my “key takeaways”:
– Know your airplane
– Maintain proficiency as best you can.
– Think through your takeoff “contingency plan” before you release the brakes.
– Don’t kill yourself trying land opposite direction on the runway you just departed from…when there’s (likely) lots of room inside the airport fence…
(Hope my AOPA dues didn’t pay for this 4-plane “experiment”)
So.now we know an aircraft will react predictably to a precise set of circumstances.
Lets hope battery technology improves considerably. Having an electric motor instead of an ICE turning your prop will make the chances of needing an “impossible” turn much slimmer.
A 5x improvement in energy density would give the Alpha Electro about 4+ hours of endurance. That level of improvement is not forecast in the near future.
However the motor controller is a sophisticated power control system with as many points of failure as a piston engine. [As an engineer, I designed DC power control systems ].
A higher power system that would power a Cessna 172, with 150 HP, would need water cooling for the motor, the controller, and possibly, the battery.
Another big problem is the battery charger that will recharge within a reasonable time and cost.?
Will your home airport acquire the $20,000 charger for you.? What bout other airports you may want to fly to ?
The Nissan Leaf Plus has a motor the equivalent of a 215-horsepower ICE. It doesn’t have liquid cooling for any of the items you mentioned and works just fine. As for the charger, if there is enough demand for it you can bet the airport will invest in it. How much do you suppose it costs to install fuel pumps and tanks?
The new 147 hp Leaf motor and controller are liquid cooled, but the 40 kWhr battery is not. [ I don’t know about the earlier 107 hp motor ]
The 60 kWhr battery is liquid cooled…maybe because some 40 wk batteries were fried due to high temps, or excessive power use.
I agree that if there is sufficient demand for chargers, some airports will install some. But, where one avgas pump is sufficient to serve an GA airport, how many chargers will be needed for the hours an aircraft will be connected to a charger ? 3, 4, 6 ?
There is no liquid cooling on the 60 KWH battery pack or the controller or motor on the Nissan Leaf. Recently I was driving around in 97 degree heat and the battery pack temperature gauge was right in the middle.
The impossible turn CANNOT BE simulated or reproduced because the flyer already knows what they are about to do. It’s much like measuring quantum particles….the more precisely the position of some particle is determined, the less precisely its momentum can be predicted from initial conditions, and vice versa (Heisenberg Uncertainty Principle).
Worse? The law of large numbers states that the more trials you have in an experiment, then the closer you get to an accurate probability. So one must make the impossible turn (suddenly and without warning) dozens or hundreds of times to make an accurate prediction.
In response to your first sentence, the experiment will not be accurate unless you include the time delay for the pilot to accept that the engine really did just quit and probably do a quick panicked check of the most likely causes/fixes. It is a bit like the situation from when the A320 went into the Hudson. Yes a test pilot who knew what was coming and what to do could make it to an airport but that did not allow for the human factor, for the time lost as the crew realizes that what they thought just happened really did. For a fair test it has to be completely unexpected or proper allowance for the human factor time delay.
Seems like they left out one approach style that has worked better for high performance aircraft and that is an immediate dive to a higher speed to perform a steep (90 deg) banked turn back to the runway and after that very tight turn climbing back to as much altitude as possible while achieving best glide speed.
The very steep turn can be considered a DIVING wingover and very little turn radius, the benefit is never getting close to a slow speed stall and only during the wingover is there and chance of stall. The rest is best glide with all the turning done as soon as possible with the highest altitude and greatest chance of success, of course pilots need some experience doing steep turns around a point.
IMPOSSIBLE TURN?
I wish people would stop referring to the “Possible Turn” as the “Impossible turn”.
If you experience engine failure after take-off, there is an aircraft/altitude/airspeed/weight/pilot combination that will allow you to complete a ‘Safe Turn’ back to the departure runway.
It was always a given that if you had a combination of the requisite items noted above, you could always return to your departure runway if you lost your engine.
The trick was to pin down the exact combination of the five items noted above that would allow safe execution of the manoeuver.
The “land straight ahead or (say) thirty degrees either side of departure path came about because engine failure in the first few seconds of take-off puts the pilot in an extremely tenuous position: no speed or altitude to trade for turning performance. Any attempt to do so resulted in a broken airplane at best, and broken people at worst.
Hence, the “never turn back” dictum.
I view the present push to train for the “Impossible Turn” with trepidation: unless the pilot
1. Is going to maintain currency (minimum 75-100 hours/year),
2. Ascertain minimum altitude for procedure commencement with dead and wind milling prop (more drag with dead engine),
3. Routinely practice the manoeuvre (which I doubt – most don’t even practice stalls/circuits),
then I don’t hold out much hope for the success in the event of an actual EFATO.
There’s nothing wrong with telling pilots to find the minimum altitude at which they KNOW they could execute a 210 degree turn back to the runway. Then add a fudge factor up to fifty percent for screw-ups.
Don’t become a test pilot on your first engine failure after take-off; half-way around the turn back is not time to find out you’re out of airspeed, altitude, and ideas…
Practice different profiles at a safe altitude in your aircraft to determine when or if you should attempt the maneuver yourself if it is ever necessary. And practice often so you stay proficient. Mentally prepare yourself before every take off for an engine out. Look at the terrain beyond the airport and have a plan before rolling down the runway. When the engine quits you’ll have precious few seconds to decide what to do. I have firsthand experience.
Amen
Double amen. During an emergency is no time to learn a new procedure, or experiment with the capabilities of the aircraft and/or pilot. Do this in advance, at altitude. Then have a plan before advancing the throttle for every takeoff.
We had a small Grumman in Ohio try it after an engine failure not long ago. He survived, the Grumman didn’t. He at least made it to the airport property, so first responders had an easy time getting to him. Also, no fire.
Airport property is usually better than a condo complex. The Grumman is more likely to stall and spin, for obvious reasons. I certainly hope the pilot had the best outcome possible, for the conditions. But the fact that he survived may be enough evidence to draw a safe conclusion.
The best bank angle to use during a return to the airport slightly exceeds sixty-degrees, with an angle of declination of about twenty-four degrees. But the object is not to stall, nor setup a descent which precludes recovery.
Those numbers apply to a Cessna 172 that is lightly loaded, under standard conditions, and they are only guidelines. The actual numbers will vary, according to conditions. Anyone who begins their testing, using forty-five degrees, doesn’t understand.
The length of the return path is determinate in the total energy dissipation, as are the g-load and resultant drag. The optimal profile is not, as most flight instructors and students assume, a steady state forty-five degree bank. That is an invalid assumption.
I understand many pilot’s hesitancy to recommend such maneuvers, especially close to the ground. But I would rather survive a den of poisonous snakes than to drown in a sea of rabbits. For many pilots, airports and airplanes, this works.
Why is there a controversy?
Thanks for posting critical information for all pilots, once again. GAN continues to be the best!
Most pilots climb away from the runway at Vy which often is a climb at 3 degrees or less. So, there’s zero chance of gliding back to the airport on a 6 degree glide path no matter what the altitude is when the engine fails. Therefore, an important component for a successful engine-out trip back to the runway is a Vx climb out while the engine is producing power all the way up to the transition altitude for cruise flight. I use 1,000 ft AGL for the transition from Vx to Vy. My plan and it works for me.
Another consideration: When the engine fails you must aggressively push the nose over to maintain a good airspeed. You will be surprised how aggressive this move needs to be. If you respond slowly, the airspeed will bleed off rapidly and be too low for a 45 degree bank turn back to the runway.
Your analysis suggests some very good thinking, but you fail to account for runway length. Longer runways invalidate your assumption.
Also…
The best bank angle to use during a return to the airport slightly exceeds sixty-degrees, with an angle of declination of about twenty-four degrees. But the object is not to stall, nor setup a descent which precludes recovery.
Those numbers apply to a Cessna 172 that is lightly loaded, under standard conditions, and they are only guidelines. The actual numbers will vary, according to conditions. Anyone who begins their testing, using forty-five degrees, doesn’t fully understand the problem.
The length of the return path is determinate in the total energy dissipation, as are the g-load and resultant drag. The optimal profile is not, as most flight instructors and students assume, a steady state forty-five degree bank. That is an invalid assumption.
I understand many pilot’s hesitancy to recommend such maneuvers, especially close to the ground. But I would rather survive a den of poisonous snakes than to drown in a sea of rabbits. For many pilots, airports and airplanes, this works.
Why is there a controversy?
John,
For the claim you make on the bank angle of slightly over 63 degree as the optimum,
can you provide the details of the flight experiment in the C-172?
1. Distance from departure end of runway for initiation of the turnback?
2.Bank angle use in the final turn to align the aircraft with the centerline? 63 deg?
3. Wind speed and direction for the flight demo?
4. Total altitude loss from initiation of turnback maneuver to the beginning of the flare over the runway.
Thanks
The Cessna 172P that I used to fly would climb at Vx at 6.6 degrees pitch, 60kts at 700 fpm. The best glide is 75 kts and the descent rate was 500-600 fpm, or -4 to -5 degrees.
So, it looks like, from the math, that if is possible to return, as the C172N did in the video.
The Cessna 175B I fly, with 180 HP, climbs at Vx at 12 degrees pitch,
[ 1,100 to 1,200 fpm at 62 mph ].
Best glide is 80 mph and 500-600 fpm, again -4 to -5 degrees.
So, the higher HP yields a lot more margin to be able to make the 360 degree return.
.
I can’t help but wonder if the 180 turn maneuver when accidentally entering IMC conditions while descending to land should also be analyzed. I have always thought the potential for spatial disorientation is unacceptably high when performing an unplanned turn, on short notice, with sudden deprecation of visual references and perhaps it should be discouraged rather than encouraged.
There were “2 Very Important Stories written (circa 1969)that most people have forgotten; ,1 in “Business and Commercial Aviation”, the other was in, “Air Progress” magazine.. If I recall, the Story/article in B and C A was entitled and posed the question to its constiuents: “WILL YOUR NEXT PILOT BE BLACK ?,
which was on the cover, there was also the picture of 3 important BLACK PROFESSIONAL PILOT’S !!!
S David Bailey aka Dave Bailey(musician)
Off topic
I wish they’d called it the “stupid turn” instead of the “impossible turn” — the latter just encouraged some people to give the stupid advice “yes, it’s possible”.
Of course surviving a 180° turn (really more like 270° for a lone runway) after an engine failure below 1,000 ft AGL is possible, just like surviving flying through a thunderstorm, flying VFR into IMC, or flying through severe icing conditions in a piston plane is possible. But unless there’s really no other choice — e.g. you just took off over freezing water — don’t do it. Too many pilots die trying, and your skills aren’t as far above average as you think they are.
David,
Did you bother to watch the video ?
It is actually a ‘possible turn, for some aircraft’.!
Not as performed in the APOA video. The first post above cites the reason. In each case, the maneuver was performed with the engine at idle. Six or seven hundred RPM provides significant thrust. Not only is that thrust not available if the engine quits, significant drag occurs from a stopped or windmilling prop. Arguably, the Cub could have made it back. I’m not so sure about the 172. Interestingly, I was about to make a similar comment on the Schiff demonstrated experiment. But Schiff ended his report with a recommendation to add a good safety margins of additional altitude to the lowest altitude AGL an individual pilot reckons the turn and return might be accomplished based on practice at a safe altitude.
When I’m doing power off 180’s to land, my engine at idle is showing 1,000 rpm, vs 600 rpm on the ground. So, the prop is driving the engine and producing drag, though maybe not as much with the engine not running.
[ I won;t test the rpm with the engine shut off. ]
The test scenarios seemed reasonable, with a 3 second wait after pulling the power to idle.
David’s comment is right on the mark. A little humility goes a long way here. How many pilots are going to keep their cool and their airspeed cushion together during a 50 degree plus Bank turning back. Would rather take my chances going in relatively straight ahead even if I had to put it in the trees – just remember to put the nose between two sturdy trees. The fuselage and you will walk away from it (some limping allowed). Stall spin alternative offers no chance of survival.