Among the pilot’s last words on Air France 447 that crashed in the Atlantic in 2009 were “This can’t be happening”, denying the tragic fact that there is no chance of survival on an aircraft that experiences a catastrophic malfunction at cruise altitude. There is always hope for survival in land and sea accidents, because these forms of transport lend themselves to safety devices like air bags, escape hatches and life boats. Commercial air transport does not lend itself to such measures though, and denial of the tragic outcome raises suspicion that something more could have been done: hence the seemingly radical idea of parachutes.
While parachutes function effectively in military ejection seats and even when attached to light aircraft, they will not work for 90% of commercial airliner accidents because those accidents occur during take-off or landing at altitudes that are too low. In the 10% of accidents that occur at cruise altitude parachutes are highly unlikely to work because the challenges of getting ready, getting out and getting down are too great.
Getting ready: Donning and adjusting a parachute takes a long time – trained personnel require at least four minutes to put on a parachute with the luxury of standing on the ground. Doing it right in the crowded confines of an airplane cabin would take longer. However the Air France accident took about four minutes from the onset of the problem until the crash occurred.
Getting out: The doors on commercial aircraft are mechanically prevented from opening until the aircraft is below approximately 10,000 feet. In a scenario like Air France 447 the descent rate is so high that the act of opening the door at 10,000 feet would consume most of the time remaining to impact, so a parachute would be of no benefit. Were the doors to open at 10,000 feet, evacuation of the air in the pressurized cabin would expel some passengers (unrestrained because they were putting on parachutes) before they had a parachute on.
Getting down: Once outside a cruising aircraft you would experience a sudden violent deceleration into cold air. A collision with the wing or tail of the aircraft would be fatal, but it is possible to miss. In that case the deceleration from being hit by the air outside is initially over 20g’s and is a form of blunt trauma. Accounting for windchill, the temperature outside will be about 40 degrees Celsius lower than on the ground. The blunt trauma and cold temperature are survivable on their own, but add to the challenge of operating a parachute for the first time.
The very short time available to put on a parachute and get out of the aircraft, coupled with the challenges of operating a parachute once outside mean that a parachute is highly unlikely to save you on a doomed commercial airliner at cruise altitude.
Your best outcome aboard a malfunctioning airliner is achieved by preparing beforehand. If you fasten your seatbelt, study the safety card, listen to flight crew instructions, know where the exits are and be prepared to leave your carry-on baggage behind, then you can take comfort knowing you did all you could.