If during flight in the Greyhawk you switch the engine off and try to steer or do anything else, the motor switches back on.
The motor needs to stay off for stealth reasons.
The airplane glides with engine off and is very useful if you are flying above enemy and is trying stay hidden as the engine is quite loud. So my goal is to glide above enemy, then get further away and switch the motor on and get away hopefully unseen.
However, if you try to steer or adjust pitch your motors turn back on.