What would happen to an airplane if the thrust reversers were to be activated while in flight?
Thrust reversers are normally used as a form of braking on the runway after touchdown but very rarely used during flight because of the heavy loss of airspeed and altitude. As others said, this does depend on which aircraft you are flying, some do not allow the deployment of TR unless you are on the ground. I will say there are also some aircraft that have reversers that are designed for in flight use, mainly for quick a descent. The thrust reverse is not an absolute reverse of engine power but better described as a thrust deflection. It does not turn the engine power around 180 degrees. There are instead mechanisms that redirect the engine power therefore disturbing the smooth forward motion of the plane causing it to slow down. Some turboprops can completely reverse their propellers, normally by changing blade angle after touchdown.
