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This question already has an answer here:

A question from the aerodynamics section of the FIA written:

Which action will result in a stall?

Incorrect answer: Flying at too low an airspeed

Correct answer: Exceeding the critical angle of attack

I could be flying in straight and level flight and if I slow down below stall speed the airplane will stall. So how can it be said that flying at too low an airspeed will not result in a stall?

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marked as duplicate by Federico, jskypilot, Peter Kämpf, Pondlife, Fabrizio Mazzoni Dec 11 '15 at 14:04

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ related: aviation.stackexchange.com/q/6366/1467 $\endgroup$ – Federico Dec 11 '15 at 12:35
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    $\begingroup$ If you reduce power, you have to pull back on the yoke to maintain altitude. As you slow, the angle of attack increases. It's the angle of attack that causes the stall, even though the reason for the angle being so high is lack of airspeed. $\endgroup$ – Steve Dec 11 '15 at 13:10
  • $\begingroup$ Thanks @Steve that is an easy-to-follow and succinct explanation. Those two qualities also make it rare for an answer on this site. $\endgroup$ – jskypilot Dec 11 '15 at 15:48
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    $\begingroup$ Yeah, now if only I was a pilot... $\endgroup$ – Steve Dec 11 '15 at 21:42
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Flying at too low an airspeed will result in a stall, but what "too low" is entirely depends on the situation. For example, if you try a very steep climbing turn, you can stall at an airspeed where you would be fine in level flight.

The answer is an incorrect answer, not because it's factually wrong, but just because it's not general enough. Exceeding the critical angle of attack always causes a stall, and it is the cause of every stall, so it's the best answer to the question. The examiner wants you to understand that the angle of attack is the mechanism that causes stalling, and that it can happen at different speeds.

It's quite common for these (and other multiple choice) exams to have an "incorrect" answer that isn't completely wrong, but isn't as good as the correct answer because it only applies in some conditions or is less general in some other way. In this case, another "incorrect" answer would be "pulling the stick back too far". That's an action that might result in a stall, if you're already at a high angle of attack, but it's not really the cause and isn't always true.

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