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3 Answers

Possible dangers of adding flaps in a turn

Asked by: 2804 views Aerodynamics, Aircraft Systems, Private Pilot

Are you more susceptible to flaps malfunctions if you try to add flaps during a turn? I think I was taught in my primary training that one flap might come down while the other one stays up, increasing the chances of a spin, so it is not advisable--or something like that. Does aerodynamics come into play to affect the flaps in an adverse way during a turn? Is this a valid concern?

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3 Answers

  1. Russ Roslewski on Apr 15, 2015

    Lots of things to consider here.

    Aerodynamically, I can’t think of anything that would make an asymmetric flap extension more likely in a turn than in straight and level flight.

    In some aircraft, asymmetric flap extension is less likely than others. For example, in Piper PA-28’s, the flaps are physically connected, and actuated, through a large connecting tube that runs under the rear seats. This thing is something like 2 inches in diameter, so it’s not likely to break. Something in the linkage between the tube and the flap itself could break, but then you would have more than just asymmetric deployment – you’d have one of the flaps just free to move in the airflow.

    An aircraft where each flap has its own actuator, of course, has more possible failure modes.

    The risk of deploying flaps while in the turn is really only for one reason that I can see – say the right flap deploys but the left one does not. You’re going to get a roll to the left. If you’re already banked over to the left in a turn, you have less time to recover before you’re at a steep bank (or even inverted). If you get an asymmetric deployment in level flight you have more time. Of course, if you’re turning to the left and get an asymmetric deployment causing a roll to the RIGHT, you have even more time to recover.

    I’m not too hard over on deploying flaps in turns, but I do have new pilots wait until they’re level. Not so much because of the asymmetric possibility, but just so the student can deal with one thing at a time – turn, level the wings, then get the flaps seems to work better for a beginning pilot.

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  2. Loral on Apr 15, 2015

    Drew – I had a flight examiner tell me of an experience he had while giving a private pilot checkride. They did have a flap malfunction which caused the plane to roll over on its back. This happened on base leg. The student froze and my friend, the examiner, had to take control. And yes, the flap malfunction DID happen when the flaps were extended in a turn so Russ is right — it can, and has, happened. From that time on, I NEVER let my students extend flaps in a turn. If it happened once, it sure as heck can happen again and I’m not looking for any low altitude heroics!

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  3. Mark Kolber on Apr 16, 2015

    No more susceptibility but like many questions involving pilot technique, the choice involves the analysis of risk and benefit (as opposed to “I do it because my CFI does it and my CFI does it because his CFI did it”).

    In the case of flap deployment in a turn, the risk of asymmetrical flap deployment is probably very low but the bad consequences if there is an asymmetrical deployment in a turn is higher than if it occurs when straight and level. The benefit of deploying flaps during the turn rather than before or after the turn is probably negligible.

    Some take the low risk/high consequences/low benefit and don’t care. Others look at the same equation and think the low benefit part makes it a no-brainer – why do something with a risk element unless there is some benefit.

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