Why is it that for the ATR 42 one of the propellers begins to rotate before of the other?

I've noticed that they also stop rotating at different times. Is there a reason for that or is it just for turning left or right?


1 Answer 1


Pilot only starts one engine at a time so the battery doesn't have to spin up both at once. At turnoff, one stop button is pressed before the other.

  • 2
    $\begingroup$ Sometimes an airplane will taxi on one engine to save fuel as well. $\endgroup$
    – GdD
    Commented Jun 8, 2018 at 11:46
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    $\begingroup$ Yeah, you start engines one at a time, unless it's a B-52, in which case you have a lot of engines to start and a very short time to get the heck out of Dodge... $\endgroup$ Commented Jun 9, 2018 at 0:23
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    $\begingroup$ Also the right engine may be running without propeller turning, because ATRs (neither 42 nor 72) don't have APU, so instead there is a propeller brake on the right engine, so it can be running without propeller spinning for power generation. $\endgroup$
    – Jan Hudec
    Commented Jun 9, 2018 at 22:16
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    $\begingroup$ @Harper-ReinstateMonica Reminded me of the Convair B-36: "Six turning, four burning". $\endgroup$ Commented Nov 18, 2022 at 10:32

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