Since the leaveVehicle function was changed in Arma 3, there is no other way to force a pilot to eject from an flying helicopter than calling 'player action ["Eject",vehicle player]', with the player as pilot in this example (Interestingly enough, the Eject function will work just fine if the pilot is not civilian). However, this brings up an error dialog saying 'Bad vehicle type ParachuteC'. I suppose the Arma 3 Dev Team should consider updating the function since it seems to be still trying to spawn the pilot with an ParachuteC.