Monday, January 17, 2011

THE IMPOSSIBLE TURN

The following article is written for publication in Pacific Flyer, by Michael Church, one of my former Flight Instructors from Sunrise Aviation in Southern California.  I find it particularly interesting and relevant as I am continually faced with how to effectively teach the appropriate response for a low altitude emergency on takeoff.  Michael sheds some light on this subject.  Be sure and watch the video.






May, 2009
Michael Church
Sunrise Aviation

GO AHEAD—TURN BACK
For the past several months I have been chiseling away at the NEVER TURN BACK credo, the cast-in-stone rule that says you must not attempt to turn back to the airport in a low altitude takeoff emergency.

It has been tough going: "NTB" has long since passed into the realm of "things we just know and never need to question."

Quite a few readers report they have watched the turn-around video I recommended (www.aerobats.com/turn-arounds.html) with positive results. Still, fifteen minutes of video is a far cry from the depth of understanding required by a real emergency. Once the engine coughs and your heart rate doubles, certainty, not theory, is crucial.

PRACTICE
The first critical key to success in turn-arounds is practice and preparation. It is certain if you don't know that you can do the maneuver safely, you won't be prepared to react as quickly as an emergency demands. Instead, you'll dither away the opportunity, then either settle for a straight-ahead crash, or conceivably attempt a turn that has by now become truly impossible.

Practice is simple: using a safe altitude, establish a stable climb at Vx (not Vy), then cut the power, noting the altitude. Allow for a couple of seconds lost in shocked disbelief, then lower the nose as you bank steeply and pull to a high angle of attack. Some level of buffet is acceptable, and inadvertent stalls are desirable as you learn where the limits are. You will be amazed at how quickly you can get turned around.

There are two fairly obvious prerequisites: first, you need to be able to make a gliding turn with a 45° or 50° bank angle without losing control of pitch.

Second, you have to be comfortable with the possibility of an inadvertent stall in a steeply banked attitude, a stall which will require recovery without rollout from the turn.

Now you see why turn-arounds are called "impossible": to the shame of the FAA and virtually the entire teaching community, few pilots are ever required to develop these two critical skills.

If this style of maneuvering is completely foreign to you, get a CFI to come along, first making sure that his or her credentials indicate they know how to do this themselves. If you get a blank look, go find another; they're out there, often identified as "aerobatic" CFIs.

ALTITUDE
Once you have developed the necessary turn-around skills, the second key to success is correct identification of a safe turn-around altitude. I'll call it STA. The number changes with three important variables, pilot skill, airplane model and density altitude and can only be determined through trial and error in a specific airplane model. Once your turn-around practice has become satisfactory, you can start the process of figuring out what is high enough and what isn't.

SET UP
The final key is climb management. If you insist at climbing at Vy, as you were almost certainly taught to do in primary instruction, no amount of skill in turning around is going to do much good. Given average runway lengths, Vy climbs are simply too flat and carry the plane too far upwind.

The liability of a flat climb is easy to see: if after a successful turn-around you find you are too far away to glide back, it is easy to argue the turn was a bad idea and only made things worse. One more win for the NTB bunch.

The bottom line: in single engine airplanes, unless you fly from Edwards AFB, forget Vy altogether below 1000' AGL. It's a poor choice.

WHY BOTHER?
My last comment: almost nobody flies as I have described, and even fewer are prepared to turn back. Yet almost everybody survives, so why bother with all this?

The answer lies in the very statistics that produced the NEVER TURN BACK credo in the first place: enough pilots have gotten killed trying the maneuver to indicate that takeoff emergencies do happen.

If you fly a single engine airplane long enough, you will experience an engine emergency. Luck plays a part, and your engine problem might occur at low altitude shortly after lift-off. If you aren't prepared, maybe you shouldn't be carrying around your family and friends.

2 comments:

  1. Sue, this is an interesting post, but I would argue that the maneuvers here weren't really flown safely. All bank angles used the same airspeed. The airspeed should really be increased like the square root of the load factor to provide stall margin. In fact, The stall horn is blaring in the 60 deg turn. Quite dangerous low to the ground. So the speeds to fly might go something like

    0 deg 65kts
    15 deg 66 kts
    30 deg 70 kts
    45 deg 77 kts
    60 deg 92 kt

    When flown this way, you have the stall margin in terms of angle of attack. You can show (I teach a class on aircraft performance) that the best bank angle for this situation is 45 deg, not 60.

    Kenneth

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  2. Hi Kenneth,

    Thank you for your comment.

    My take on this is that they were using the best glide speed of 65kts for a typical C172, late 70's/80's vintage, to get the best gliding distance during engine failure. (changing the airspeed will undoubtedly get you to the ground quicker and probably wide or short of your destination.

    If you go to the performance section for the same vintage and look at the Stall Speeds page, worst case scenario without flaps for a 45 deg bank is 52 KIAS, (quite a distance from the 65 kts being flown-seems very reasonable)and for a 60 deg is 62 KIAS, still under the stall speed, although closer. Not sure why you are suggesting a 25 kt and a 30 kt margin respectively, especially in an emergency.

    Since most stall horns are "warning" horns and designed to start "warning" 10 kts above stall speed, the fact that the horn was audible is understandable.

    I doubt that the recommendation is for 60 deg for a novice pilot and without putting in some considerable practice. Afterall, if you can't make the runway, it is better to have the aircraft under control and land off airport, than enter a stall in a turn.

    Knowing the two instructors that put this presentation together, I would suspect that the impetus is for other instructors to train their students to some proficiency in this maneuver.

    Sue

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