Steep turn

The impossible turn, for those of you not familiar with that term, refers to a single engine aircraft losing power after takeoff and executing a 180-degree turn and landing successfully on the same runway from which they just departed. The FAA’s official recommendation on losing power after takeoff is to proceed straight ahead and not to attempt to return to the runway or airport. That existing policy position by the FAA assumes there is an open area available for a successful touchdown. The second assumption is that pilot skill level is not sufficient to execute a 180-degree turn in order to return to landing without stalling and spinning in. Both positions are not much help.

The best advice at this time comes from the aviation master Bob Hoover. To quote: “Fly the airplane as far into the crash as you can.” Or as my original flight instructor once told me while discussing the subject, “Pick out the cheapest thing available and aim for it.”

Steep turn

To make it back to the runway, the nose must be lowered and the bank must be 45 degrees.

Right now there are thousands of CFIs conducting touch and goes or options around the country. On the 1500 touch and go around the pattern and just before turning crosswind, they get the idea that it would be possible to perform the so called impossible turn and quite easily too.

Now, as I approach my 50th year of flying, aviation, engineering, and flight research, I can recommend an engineering approach along with my flight training experience on how to successfully conduct this emergency flight procedure.

So like any sound engineering and research project, we begin by asking ourselves the following:

  • Is there any literature on this subject?
  • Has this subject been researched before?
  • Is this emergency procedure maneuver conducted now?
  • Can this 180-degree turn existing maneuver be applied to single engine aircraft?

The answer to all of the questions is yes!

The literature search

Some time ago, I was lucky to locate several texts both published in 1947. The first, Airplane Performance Stability and Control, by Robert E. Hag and more importantly Technical Aerodynamics by Karal D. Wood.

Mr. Wood addresses the problem succinctly on page 289. He states, “Calculations on gliding turns are of practical importance because they permit determining the minimum altitude from which a return to the airport is possible in the event of motor failure soon after take off…”

Without reviewing the recommended math calculations here, he states this would show and determine helical path that may be considered wound on a cylinder and the altitude loss in completing a turn. The equations can solve for minimum loss of altitude in gliding turn.

He further states: “for minimal loss of altitude it can be shown that an angle of bank should be about 45 degrees and the wing should operate at maximum lift.”

So, what do we have here?

Mr. Wood has provided us with two data points:

  1. It is aerodynamically possible to execute a 180-degree gliding turn successfully back to the runway.
  2. An angle of bank of about 45 degrees may be used to do so.

So far so good. Now what is needed is the altitude to execute this maneuver, which way to turn (left or right), and why.

Approved FAA flight test standards and advisory circulars, along with accepted training manuals, provide an answer to our first questions: Is this emergency procedure maneuver conducted now? Can this 180-degree turn existing procedure be applied to single engine aircraft?

Our brethren who fly and instruct in helicopters and gliders practice this impossible turn while teaching and obtaining their respective ratings. With respect to our literature search, we will reference two glider publications plus an unlikely approach.

Glider tow

Glider pilots practice rope breaks all the time—their version of the impossible turn.

Gliders 

  1. The Joy of Soaring, a training manual by Clark Conway from the Soaring Society of America.
  1. The Art and Technique of Soaring, by Richard Walters.
  1. It may be somewhat out of scope for this subject but the Space Shuttle—which is also a glider, by the way—had an emergency, 180-degree turn procedure. Fortunately, it was never used. I refer to the Return to Launch Sight, or RTL, emergency maneuver. When free from the solid rocket boosters and jettisoning the external tank, the shuttle was to execute a modified split-s maneuver and attempt to return to the runway. A gutsy maneuver to say the least. However, this proves the space shuttle did have an emergency plan if the need arose.

Soaring publications refer to the so-called impossible turn, known in the soaring world as the rope break procedure. Gliders are launched into the air by air towing from another powered aircraft referred to as a tug. Briefly stated, both publications recommend the key decisions height or point as 200 ft AGL.

Below 200 ft., recommended procedure is to land straight ahead. Above 200 ft., the rope break procedure is recommended to a downwind landing. At 1000 ft., a normal arrival traffic pattern is flown. So now we have two altitude recommendations to work with: 200 ft. and 1000 ft.

On the subject of which way to turn, turn into the wind. A turn into the wind will provide the least radius of action in the turn. Turning with the wind will cause the aircraft to drift away from the runway. The time spent realigning with the runway centerline may not allow completion of the turn or proper alignment with the runway allowing for a successful landing. Airspeed used by gliders is known as best distance speed. In a powered aircraft it would be best glide speed.

This is where we do not want the aircraft’s nose on or above the horizon. Keeping it there will get you into an accelerated stall. Not something you want close to the ground. Keep your nose below the horizon and your best glide speed. Let the aircraft proceed in a controlled spiral as stated previously by Mr. Wood.

Helicopters

Our helicopter brethren have an easier method in determining the best altitude and airspeed to employ in executing the impossible turn. In helicopter training and in actual emergency procedure, the student is introduced to the 180-degree autorotation procedure.

HV diagram

The HV diagram tells helicopter pilots where they are out of energy for an autorotation.

Altitude and airspeed for this maneuver is provided by a HV diagram or velocity/altitude graph. The graph shows altitude scale on the vertical axis and airspeed on the horizontal axis. Shaded areas on both axes indicates areas that autorotation, or engine out procedures, are not recommended. Read that as not successful. This H/V diagram can be found in Helicopter Flying Handbook 8083-21 on page 11-8.

Conducting my first 180-degree autorotation it was an eye-opening experience. Looking directly down is not recommended by the instructor. I did look anyway. It really got my attention and caused me to say bad words. The instructor found this very funny as I recall.

So important is this maneuver to the FAA and helicopter operations that this subject of 180-degree autorotation is also addressed in AC-61-140, Autorotation Training.

Why the comparison? Well gliders, while having a great lift to drag ratio, are somewhat slow in turning. What that means is while they stay up longer they do not turn quickly. Helicopters are handicapped by not having much of a glide capability, often referred to as the glide ratio of a crowbar. However, they can turnaround in their own airspace. Fixed wing aircraft fall somewhere in the middle. My 1939 Aeronca has a glide capability not unlike a Schweizer 2-33 training glider. A Cessna 172 easily performs an impossible turn. This type of emergency procedure both glider or helicopter must be done without hesitation. Both procedures are required training maneuvers that are demonstrated by the instructor and accomplished by the student before proceeding to the checkride.

Training and dog bones

So, what do we have to begin with? Mr. Wood has proven aerodynamically that it is possible to successfully execute a 180-degree turn with a bank angle of about 45 degrees.Our helicopter brethren train for this maneuver employing a HV diagram for altitude and airspeed in which to operate. The glider community employs 200 ft. AGL as the desired altitude, knowing the direction of the wind to determine which way to turn and keeping the nose below the horizon to avoid stalls in the turn. Both are required maneuvers.

Dog bones is a slang term for an abbreviated traffic pattern. After departing, make a 180-degree turn and land on the same runway downwind. Runway length permitting on touchdown, add full power, climb out and again cut the power and execute a 180-degree turn, landing on the same runway—this time into the wind. The name dog bones comes from the pattern the aircraft makes over the ground.

This procedure can be repeated until boredom sets in or ATC needs the runway. I have done this maneuver with students in various single engine aircraft in day and night conditions. During the day, this procedure is fun and after several tries the students really enjoy it. Night is more fun as you usually have the airport all to yourself. Have an experienced flight instructor show you how to conduct dog bones before trying them yourself.

What aircraft you fly will determine the altitude you know you can conduct a 180-degree turn and align with the centerline of the runway. When you are comfortable with handling the aircraft and noting how much altitude it would take for you to turn 180, that altitude would be your go-to altitude after takeoff.

Starting high at 1000 ft. is a good altitude. You know the best glide speed for your aircraft, or you should know it. Remember, do not keep your nose on the horizon when turning; keep it below the horizon, fly the spiral as stated, and a bank about 45 degrees or less. DO NOT rush or pull the aircraft around and tighten up the turn. Doing so will get you into an accelerated stall.

Remember, this is an emergency procedure.

When conducting your dog bone pattern, you will establish your comfortable altitude from which you know you can successfully execute the maneuver. Remember, your bank angle is about 45 degrees and do not exceed that. You know your aircraft’s best glide speed. Now you have the altitude you need, your aircraft’s best glide speed, and the experience you need to execute this emergency procedure.

When practicing this maneuver, you can add power when you find yourself not aligned with the runway or coming up short. Landing downwind will be tricky at first but with a little practice you can overcome the new experience and soon master it. In a real emergency, ground effect will carry you farther than you might think. If not, well, there are not many obstacles just off the end of the runway and taking out several runway lights is a small price to pay vs. an off-airport landing. It’s the best of a bad situation.

Find a good CFI, practice this often, and keep it in mind it is an emergency procedure to get you out of a no win situation.

Fly safe and let me know how it works out for you.

14 replies
  1. Michael Bernhart
    Michael Bernhart says:

    At last, an intelligent approach to the question. Many (most?) of us fly out of airports that have been swallowed up by cities and ‘burbs. Straight-ahead is often a poor option. The author stops short of recommending the minimum altitude needed. Some thoughts:

    The altitude lost in a 180° turn is a function of drag and time. Induced drag is fixed once the plane is in the air (weight, wing loading, airspeed). It takes a certain amount of energy/lift to reverse course, whether done at 20 degrees of bank or 60. The amount of bank has little effect on the induced drag accrued in a turn; however, it does determine how long the a/c will be in the turn and subjected to parasite drag.

    Bank angle has a significant effect on how long it takes to complete a 180. The formula for rate of turn is 1,091 x (tangent of the bank angle)/TAS. Because the tangent goes up with angle of bank any increase in bank will increase rate of turn and any increase in speed will reduce it. And since the distance between a dead-stick airplane and the ground can be measured in precious seconds, an expeditious rate of turn is desirable. To point out the obvious, more bank and lower TAS are what you want (with an eye on best glide speed and stalling speed as g’s increase). To illustrate, a 180° turn at 30° of bank at 85 KTAS takes 24 seconds to complete; a 180 at 45° takes 14 seconds; and a 180 at 60° can be completed in only 8.1 seconds. Double the bank from 30 to 60 and cut the time needed to head back to the field from 24 to 8 seconds. The steeper bank has the added advantage that the offset from the runway is less on rollout.

    Yes, we are all aware that steep-banked turns near the ground invite a stall. A 2 g tug on the yoke will stall my 20E at 90 KIAS; coincidentally, 2 gs are required to hold a plane in a stable 60° bank turn. Not much room for error when you slip below Vy and crank it over to 60° of bank.

    Several iterations (at altitude) in a Mooney 20E yielded average altitude losses in a 180° turn of:
    350′ lost at 30° bank,
    270′ lost at 45° bank, and
    220′ lost at 60° bank.
    These were entered and flown at 90 KIAS since that is the a/s I often see as I clean up the plane during initial climb out. TAS was 100 knots.

    It’s important to bear in mind that these figures are from a slippery Mooney which suffers famously little parasitic drag. Consider the coefficient of parasite drag for several popular GA planes:

    Aircraft Cdp Flat Plate Area (sq. ft.)
    Mooney 201 0.017 2.81
    Beech Bonanza 0.019 3.47
    Piper Arrow 0.027 4.64
    Cessna 182 0.031 5.27
    Beech Sierra 0.034 5.02
    Piper Warrior 0.034 5.83
    Cessna 172 0.036 6.25
    Cessna 152 0.038 6.14
    Beech Skipper 0.049 6.36
    Piper Tomahawk 0.054 6.64

    The altitude loss in most other GA aircraft is going to be greater than in a Mooney. Run your own experiment to get a sense of how much altitude you would need to consider the ‘impossible turn’. Also, a lighter aircraft (Mooney, again) will not pay as high an induced drag penalty as one with higher wing loadings. My recommendation is to try several power off 180°s in your plane.

    What else? Mitigating/complicating factors include:
    Obstacles. The runway may be the lowest lying thing around. Do you need more altitude to clear trees, buildings, power lines, etc?

    Alignment. A 180 may not be the end of the turning if you wind up having to make two large corrections to angle toward a runway and then line up with it. You can reduce rollout alignment problems by allowing the plane to drift downwind after liftoff, or, in the absence of a crosswind, by turning a few degrees off runway heading. Or, my situation, a parallel runway – or a taxiway – may be there, waiting to receive you on rollout from your impossible 180.

    Climb angle. If your experience or conditions (short runway, meager vertical velocity) indicate that Vy would provide such a shallow climb angle that you will be so far from the airport that there’s no point in turning around, consider an initial climb closer to Vx – bearing in mind that a slower rate of climb is inevitable on a hot day and the engine is paying the price.

    Dithering. Don’t! Crank it over past 45° asap. If the engine comes back to life you’ve lost nothing and can level your wings while explaining to ATC, in your best Chuck Yeager voice, that you’ve just dealt with a minor hiccup.

    Restart? There’s not much you can do. In my E the fuel selector is almost inaccessible and your boost pump is already on, right? (But, doesn’t hurt to check it.)

    Planning. Three items to consider before you take the active: a) Decide if you want an initial climb at Vy, or closer to Vx, b) how do you plan to obtain some lateral distance from the extended runway centerline to improve alignment after completing the impossible turn, and c) are there obstacles that would factor into your decision altitude or direction of turnback.

    The take-away
    For what it’s worth, this research and in-flight experimentation led me to the following:
    1) Initial climb at Vy – or Vx if necessary.
    2) If a cross-wind, allow plane to drift off centerline (if no parallel runway) or turn 10° to gain lateral distance.
    3) Call 300′ as the altitude at which the ‘impossible turn’ becomes feasible (in my Mooney! Determine your own plane’s performance.)
    4) Engine failure, rack plane into 45 – 60° banked turn, heading into the crosswind if there is one. The nose drops automatically in the steeper bank – if you’ll allow it.
    5) Pull prop to feather. (Increases the Mooney’s glide ratio almost 20 percent; Bonanza reportedly similar.)
    6) Maintain Vy.
    7) Notify tower to break out the ticker tape or marshmallows.

    I would not challenge the 1000′ rule but for the location of the airport (PDK, in my case). Rural airports? Forgot all this and glide into the nearest pasture ahead of you. But if, as for many departures, there’s nothing but innocent civilians in your path, know the altitude at which the ‘impossible turn’ is possible. Then practice it aloft and think it through be-fore each departure.

    • Pete Hodges
      Pete Hodges says:

      Thank you for such a great article and thoughtful comments on this subject! I always thought a 180 to the runway should be one of the options for an engine out scenario. I owned a Hershey bar Cherokee for 14 years and one day I decided to try it. I did a normal climb to 750 feet and pulled back the power, I established a straight ahead glide for a few seconds to simulate initial confusion, then turned into the wind about 40 degrees. I ended up turning about 220 degrees to get to the center line, and rolled back the other way to line up. I landed in the first 20% of the pavement and the was good enough for me at the time. I now own a M20E and loved your thoughtful comments Mike. I can’t wait to try them out for myself.

  2. David Megginson
    David Megginson says:

    Interesting article. If you’re close to the airport, and landing on the field, a taxiway, or a different runway isn’t an option, I think you’ll need more like 270° of turning to line up, but you could still calculate that in.

  3. Joshua D Anderson
    Joshua D Anderson says:

    You’ve got a lot of credentials, and I more or less agree with your conclusions, so I Hesitate calling you out, but #1, your comparison to helicopter 180’s is completely inaccurate. Standard Helicopter 180 engine failures are practiced nearly the same as standard airplane 180 engine failures… from high on the downwind, 200’aside the runway, abeam the numbers, not on takeoff(Chen the HFH if you’re curious) The physics of the “impossible” turn are only slightly better for a heli than an airplane, and the H/V curve does not allow you to cheat the fact that you have to get 2000lb of metal to not only reverse direction, but also regain enough airspeed in that new direction to flare to a soft landing and maintain enough rotor speed to keep it flying (likely with a tailwind, also putting you at a much higher risk of getting into VRS at the end of the auto when pulling pitch with a tailwind) That h/v diagram you show is for straight ahead landings during engine failure, mentions nothing about whipping a 180 on the spot, and I challenge you to find one that does. If it’s out there, I promise it will look a whole lot different because that takes more altitude.

    #2 how is this an engineering approach? There are no real calculations done? What would be more useful is a conversation about the physics involved in, and the high value of a steeply banked descending (helical as you say) turn. All these textbook answers about load factor that the FAA has us memorize are kind of pointless because they are for a level turn maintaining altitude. If you point your nose down and quit fighting gravity, you can turn steeper with less load factor, with the added bonus of picking up airspeed through the maneuver that will keep to further away from stall/spin accidents, and as long as you speed build isn’t to excessive, that energy is largely retained and converted back into reduced descent rates when you need it. Long story short, I agree that steep bank descending turns into the wind are best for the impossible turn, but calling this an engineering approach is a bit of a stretch without further calculation

  4. Mikehamlett
    Mikehamlett says:

    Bear in mind if you took off with a 10 Knot headwind you need to accelerate the aircraft by 20 knots ground speed to get the same airspeed going 180 degrees back to the strip. Maybe that is why so many stall and spin trying to turn back.

  5. JOHN SWALLOW
    JOHN SWALLOW says:

    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 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 those four items ‘pinned down’, you could always return to your departure runway if you lost your engine.

    The trick was to pin down the exact combination of the four 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 can execute a 210 degree turn back to the runway. However, like surface aerobatics, this is not something you practice once a year…

    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…

    PS Concur with the comment about helicopter 180 autos: I’ve literally done thousands. If you lose the engine in a helo on take off; down collective, and look for a reasonably open area within (say) forty-five degrees of the nose. That’s where you’re going to be in less than a minute… (;>0)

  6. Ed Wischmeyer
    Ed Wischmeyer says:

    While there have been any number of discussions about best bank angle / speed combinations, from my engineering perspective, these are oversimplifications. More appropriate discussions would come from using calculus of variations and from optimal control theory. Those are much more involved than can be discussed here and were unknown in 1947. Moreover, nobody seems to talk much about how precisely a stressed pilot can fly a bank angle and airspeed profile at low altitude — and does anybody ever practice that? And, yes, I’ve got letters after my name too, for what it’s worth, ATP/CFII, Ph.D. from MIT.

  7. grant
    grant says:

    Also, the relative risks of both maneuvers must be considered:

    Stall- spin from low altitude? Inevitably deadly.
    vs

    Forced landing, more or less straight ahead, “flying the plane as far into the crash as possible?” Often survivable. Sometimes the airplane is even reuseable…

    hmmmm…

  8. Vince MASSIMINI
    Vince MASSIMINI says:

    I recommend against the turn unless you have practiced it in that aircraft (or at least the model and engine). Note that many aircraft, if not most, will not have the energy to make the runway unless you climb at Vx and have some headwind on takeoff (or have a very long runway. That’s because the glide angle is steeper than the climb angle for most aircraft. So, before you get real cocky about turning back, try it in your aircraft.

Comments are closed.