Just using common sense
Helicopters - Obviously the rotors
Airplanes - People aren't trained to use it correctly, sucked into engines, expensive.
Aircrafts are designed to be very safe, we like to have the probability of any event happening remain at 1E-9 or lower. Most crashes are caused by pilot error and you will not know something is wrong unless they tell you. Things like engine fire and such are recoverable events, an aircraft can fly with one engine and can glide with no engines. So the chances of the pilot going through all the instructions to recover the aircraft then failing (which is extremely improbable) then going onto notify the passengers to get their parachutes on and use it correctly that is impossible to control in a high stress situation.
And to be completely honest, it will be way too expensive.