On final in a C182T you move the flap control arm from 20 to FULL, and when halfway there, the breaker pops (or BUS1 fails, a wire falls off, etc.)

Does the flap stay where it is, slide back to 20°, slide back to UP, or something else? Perhaps the question is “are the stops mechanically significant?”

Would the answer change if instead of blackout it was a brownout? I.e. the motor is still trying to run, but doesn’t have all of its normal oomph.

  • $\begingroup$ @quietflyer Are you seriously suggesting that someone (who presuamably isn't a test pilot) deliberately disable their aircraft, while in the air? $\endgroup$ Jun 20, 2019 at 11:50
  • $\begingroup$ Never mind, I suppose with fancy glass panels and what-not-all kinds of electronic engine systems, you probably don't want to do that. No, I'm certainly not suggesting anything whatsoever. He could stand outside the plane on the ground and have someone switch off the master while the flaps were in transit, maybe even while he applied gentle pressure on the moving flaps by hand. If I were flying a more basic sort of a Cessna though, I certainly wouldn't consider switching off the master to be "disabling". $\endgroup$ Jun 20, 2019 at 12:01

1 Answer 1


Stays where it is. The mechanism is a leadscrew and like most leadscrews it's "self-locking", which means that it's held in position by frictional forces whenever the motor isn't turning and it can't be back-driven even by substantial loads. The 20 degree (etc) "stops" are just reference positions for which aircraft performance and load limit data have been determined.

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    $\begingroup$ I would think if there are 2 motors, the stops also provide assurance both wings are in the same position. You wouldn't want to, say, run both motors for 5 seconds and hope they move to the same position... $\endgroup$ Jun 19, 2019 at 15:56
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    $\begingroup$ @Harper the flaps on both wings are joined by a mechanical linkage that ensures they always move together. There is only a single motor that drives both. Having separate motors and separate mechanisms per wing with no rigid linkage between wings would be quite a dangerous design unless extensive (& expensive) extra safety systems were incorporated to prevent asymmetric deployment. Such complications may make sense on a transport-category aircraft where the longer wingspan and cabin arrangement prohibits the simple approach, but they wouldn't make sense on a light GA aircraft. $\endgroup$ Jun 19, 2019 at 16:03

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