Does an engine have to be at idle thrust for the reversers to deploy? If the engine is at higher than idle thrust, will it slow down to deploy the reversers and then speed up again, or can it just deploy the reversers at the higher thrust?

I am also asking about turboprops going into beta range.

I had this question based on the discussion on this question:

What to do when you accidentally land on a runway thats borderline long enough to land on?


2 Answers 2


Engines must be at idle thrust to enter reverse thrust. This may not be 100% true of the physical action of engine entering reverse thrust (opening the buckets or translating the cowling), but it is required by the thrust levers. In all airplanes I'm familiar with the thrust levers must be at idle to enter the reverse regime, In the EMB-145 the reversage was below idle (i.e. you keep moving the levers aft) through a gate. Even if the engine is capable of entering reverse thrust not at idle, there is no way to command it without first being at idle.

  • $\begingroup$ Yep, worst case is that you quickly retard the throttles from a higher setting to idle and then into reverse, and the engine hasn't spooled down completely by the time the buckets come out (or whatever). Some planes may have some kind of protection system that monitors N1 but I don't know of any specifics there. $\endgroup$
    – TypeIA
    Apr 30, 2014 at 20:05

On 747-100 and -200 aircraft, each reverse thrust lever is mounted on the front side of it's respective thrust lever with the hinge above the reverse lever's end knob. If you should happen to grab the reverse thrust lever without having the forward thrust lever all the way back, the action of lifting the reverse thrust lever will force the forward thrust lever all the way back. When you lift reverse thrust lever to an almost-level position from it previous position parallel to the forward thrust lever, the buckets come out. That in itself provides considerable braking, and it's common to stop there. Continuing to lift and then bring back the reverse thrust levers spools up the engines. You need to be careful doing this. Coming back too far too fast might cause a compressor stall, especially on an already marginal engine. Compressor stalls on a Pratt and Whitney engine are no big deal. On a General Electric engine they are far more serious. As I remember, there was a lock-out that prevented an engine from moving into reverse thrust from other than idle thrust, but I can't remember how it worked, but I believe it required not just idle thrust but the aircraft also being on the ground (squat switches) and landing flap deployment.

  • $\begingroup$ Why are compressor stalls so much more serious on GE engines? $\endgroup$
    – Vikki
    Jun 10, 2019 at 2:09
  • 1
    $\begingroup$ @Sean I don't know the answer to that. Of the 23 747s the airline I retired out had at the time of my retirement, only one had GE engines, and I don't recall ever hearing of a compressor stall on it. All I can tell you is that we didn't write up compressor stalls on P&W engines, but were instructed to write up a GE compressor stall, which would mean maintenance would have to take a look at the engine. $\endgroup$
    – Terry
    Jun 10, 2019 at 23:26

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