Airplanes are inherently stable. That means if you take your hands off of the controls, the plane will return to flat and level flight.
This is unlike helicopters, that take constant control inputs to maintain flat and level flight. Flying a helicopter is like standing on a basketball, constant movement is needed to stay on top.
An airplane is much easier to deal with in an engine failure, just push nose slightly towards ground and you will glide.
With helicopters you need to use your speed falling to rotate the blades, then at the last minute use the momentum of the blades to stop the helicopter falling. A much more difficult maneuver.
The other issue is helicopters fly in more challenging missions. Airplanes are usually airport to airport. Helicopters are used for rescuing people in mountains, medivac injured people from random locations, maintenance of power lines, filming etc. The tend to be low to the ground, dangerous locations etc where there isn’t much time to deal with an accident.
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