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I understand that commercial flights are equipped with life vests. I also understand that most military jets are equipped with ejection seats. It may be costly and technically challenging to equip passenger planes with ejection seats. Having seen air-borne personnel lining up and parachuting out of a C130, what is preventing flights from equipping each passenger with a life-saving parachute? Is it very technically challenging for an untrained person to deploy a parachute, or are there other reasons?

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Maybe because of blackouts (oxygen suffocation), redout (spinning too much in the air) and responsibility (better put it on the pilot and crew, who can be trained extensively, rather than the passengers?). Disclaimer: I am not working in the field. –  user1121352 Mar 12 at 19:39
@QuestionOverflow I've reverted your edit with the point/counterpoint discussions - You raised some excellent discussion points, but please provide those "counterpoint" arguments in the comments under each answer (that's what comments are for). The goal of the Q&A format is to keep the question as a question, not a discussion of the answers (see aviation.stackexchange.com/about & aviation.stackexchange.com/help/how-to-ask) Thanks :-) –  voretaq7 Mar 12 at 21:35
A better solution would be to have parachute system that protects the entire aircraft.Price out the cost of ejector seats. –  Noah Spurrier Mar 13 at 0:26
See also this question, which has a detailed answer on the use of parachutes: What items could you bring on-board to maximise your chance of survival in an emergency? –  Danny Beckett Mar 13 at 5:18

12 Answers 12

up vote 39 down vote accepted

Qualification: I worked at a sport parachute center as an instructor for 10 years and I hold an FAA Master Parachute Rigger certificate. I believe that qualifies me as an expert on the subject.

The majority of the above other statements here are correct. In summary:

  • The door of a pressurized passenger plane cannot be opened in flight for the stated reasons.

  • the door of most larger passenger planes cannot be opened in flight after you depressurize the cabin because they swing forward. Push a sheet of plywood against a thunderstorm-grade wind and see how well you do. Now multiply the wind speed by 5.

  • even if you blow the door out with explosives, the chances of an orderly exit are slim. At airliner speeds an orderly exit is critical if you expect to survive the jump. Street clothes will be torn to shreds. Oh, and it's COLD up there.

  • you cannot depressurize an aircraft over 12,000 feet altitude without the passengers passing out rather quickly. If you can control the plane down to this altitude, you don't need the parachutes.

  • it is extremely difficult to exit an unstable aircraft that is built for sport parachuting (in-flight door, suitable handles, door already open). If the plane is spinning and you are beside the door you might get tossed out and then struck by other parts of the airframe. If it's a larger plane and the door (or you) are away from the current axis of rotation, good luck. Yes, jumpers have successfully exited a crippled jump plane. None of them want to try it again.

  • modern sport parachutes use steerable ram-air canopies. Jump one of these without any training and you will hurt yourself landing. Most emergency parachutes are round. Jump one of those without any training and you will break something when you land. 200 untrained people jumping ram-air canopies all at once will result in a number of collisions and entanglements, which are typically fatal for all involved.

  • exiting an airplane below 1000 feet is really not practical. I would do it IF a) the plane is currently under control; b) landing is not practical; c) It's really 1000 feet, not less; d) I'm sitting beside the door. Possible scenario is the engine goes boom and I know there's nothing but rocky land ahead of us. Of course my gear is already on my back ready to go, and I know how to use it.

There have been many cases of a jump plane experiencing engine problems on the way up. By the time the pilot turns around, the cabin is usually empty. There have also been cases where jump planes have crashed on takeoff. None of the (very experienced) jumpers on board thought about anything other than tightening the seatbelt.

Points I disagree with: (although they do not change the outcome)

  • Emergency parachutes (seat-pack types) are available for far less than sport rigs. Maybe $1,500 each. Weight around 8-10kg. Putting a purpose-built one on would be not much more complicated than a 4-point harness. This was seriously considered back in the 1950's - aircraft seats were designed with parachutes built in. Planes were neither pressurized nor fast back then. Think DC-3 era - the DC-3 makes a great jump plane, I have used one a few times.

  • maintenance costs would be no more than the escape slides, flotation gear or other similar equipment.

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Thanks for your input. One quick question. If the airplane is tearing up in mid-air and plunging towards the ground in 1 or 2 min, would you prefer the parachute option or the seat belt option? –  Question Overflow Mar 13 at 12:51
@QuestionOverflow If the plane is tearing up in mid air and plunging towards the ground, the preference is academic: you're going to die. –  David Richerby Mar 13 at 15:50
What he said. If the plane has suffered catastrophic failure (e.g. mid-air collision) your chances of survival IN the plane are zero. You have a moderate chance of being chopped up by the propeller (all jump planes use props). If you get away from the plane it's just another skydive. The pilot will be right behind you. Our pilots generally had zero interest in jumping, all said they would bail if the plane was uncontrollable. –  Paul Mar 14 at 12:55
@DavidRicherby I think the point Question Overflow is getting at is that most people would prefer a .0001% chance of survival to a 0% chance of survival. Yeah, the odds are rather long, but having a parachute would at least, minutely, improve the chance of survival. ...I think the real question we ought to be asking is this: is anyone willing to spend $200 extra a flight so planes can carry the parachutes, train the staff, train the pilots, make better walkways (etc) for something that is extremely unlikely to happen. Assuming it would even be that cheap? My guess, honestly, is no. –  Jay Carr Mar 14 at 13:02
@AyeshK: 12,000 feet is a standard jump altitude for several reasons: it is easily reachable by a single-engine Cessna (most common jump plane), high enough to provide 60 seconds of freefall, and not so high you need supplemental oxygen onboard or interfere (much) with commercial air traffic. The highest I have jumped is 16,000 feet - the airport looked really small and I was a bit bored on the way down. The air is noticeably thinner (and colder) up there too. High-altitude drop zones like Denver CO often stop at 9,500 feet. –  Paul Mar 21 at 13:20

Parachutes are heavy, expensive, difficult to use and will be useless in pretty much any air disaster.

In order to parachute from a commercial aircraft it would need to be

  • in a stable attitude,
  • at low speed
  • and below about 12 000 ft.

Short of an aircraft losing power to all engines like the Gimli Glider, in which case ditching in the ocean or finding an open space to land is preferable to parachuting your passengers out, I can't think of any other catastrophic failure that would give you the opportunity to let passengers leave by parachute.

That's aside from the difficulty of trying to get passengers, most of whom are panicking, to properly don a parachute and tighten the necessary straps. With a lifejacket a person can still hold onto it in the water if they didn't do the straps right, but the same is not true for a parachute.

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Also, you're presumably going to end up with your surviving passengers spread over a rather large area. For every minute your evacuation takes at 150kt, your passengers are spread over a 2.5nmi length, even if they fall straight down. Standard evacuation times won't apply since (a) you can only use the rear doors and (b) a significant proportion of the passengers will need some persuasion to jump. And, as alluded to by the answer, if you can fly your plane slow and level enough for parachuting, it's probably in good enough shape that you don't need to evacuate. –  David Richerby Mar 12 at 11:00
@QuestionOverflow Trivial Googling suggests that a parachute backpack costs somewhere in the region of $6-8k and weighs 10-25kg (15-55lbs). So, for a 150-seat B737, you're talking somewhere around a million bucks' worth of parachutes, weighing 1.5-4 tons. Also, note that bomber crews are (a) trained and (b) small. –  David Richerby Mar 12 at 11:09
@AdityaPatil Is that a serious question? If so, try this: you'll need a friend or two to help. Stand in a doorway with the door open away from you and place your feet against the wall, outside the door frame. Brace your hands against the frame at shoulder height. How long does it take your friend(s) to push you through the door while you're wedged against it like that? –  David Richerby Mar 12 at 11:36
@AdityaPatil that only works if people are thinking rationally. In an emergency most people are going to panic and rational thought will not occur. –  Dan Neely Mar 12 at 13:12
Also worth considering is the fact that most aircraft crashes don't actually kill people (most statistics show aircraft crashes with at least 100 fatalities - somewhere around 10 of those per year). As long as the plane didn't actually disintegrate (chute aren't going to help you there), the chances of survival aren't negligible - the overall rate is somewhere around 35%, including the cases where chutes wouldn't help either. So your best bet is to stay on the plane, unless you're a trained paradropper, especially since you're not landing on a prepared landing site - very hard. –  Luaan Mar 13 at 8:54

The main reason that parachutes are not used is that there are very, very few aircraft accidents that occur with enough time to actually use one. In fact, I'm not sure that there have been any. Below are a couple examples that you may originally think that parachutes could have been useful on because they initiated from a high altitude.

Air France 447:

The short version is that they stalled the airplane at cruising altitude and held it in the stall until it crashed into the ocean.

Let's consider that the amount of time from the peak altitude of the aircraft until impact with water was only 3 minutes and 21 seconds. Let's be very generous and say that everybody on board immediately knew that the aircraft was going to crash and there was nothing that the pilots could do.

This gives the panicking passengers just over three minutes to get their parachutes out of storage, properly secure themselves into the harness (which, trust me, isn't as easy as it sounds even if you know what you are doing and are in the proper frame of mind), all while in the confined space of an aircraft seat with everyone else around them doing the same thing. After that, we somehow need to open the doors and get people to orderly line up and exit the airplane without freaking out and getting scared.

Seriously, 99% of the people won't even get their parachute on (correctly) in that amount of time, much less the far less time that they would really have before they knew about the crash.

The reality of the matter is that the pilots are doing everything possible in an emergency situation to not crash in the first place, and if they are successful (which they usually are) then having everybody jump would have caused many more problems than having the passengers stay put in their seats with their seatbelts on. In this particular crash, the pilots didn't even realize that the crash was certain until four seconds before impact when one of the pilots verbally stated "we're going to crash". Up until that point they were focused on recovering the aircraft and probably would never even have given the evacuation order had it even been available.

Gol Transportes Aéreos Flight 1907

This was the mid air collision over Brazil. At least in this case, it became certain pretty fast that the aircraft was out of control and was going to crash.

A small quote from the accident report describes what happened immediately after the collision:

Immediately after the collision, PR-GTD started a fast descending spiral, similar to the maneuver known as spin, which by no means could be recovered or controlled by the crew. During the vertiginous dive, the aircraft was submitted to extreme aerodynamic forces, around all the axes, with positive and negative accelerations, well above the maximum resistance limits of the operational envelope. As a result, there was an in-flight break-up of the aircraft in several pieces of different sizes, which hit the ground.

The increased G forces on the airplane were very likely to the point that people couldn't stand, or at the very least would have a much harder time doing so. Trying to put a parachute on in these circumstances would be even harder than in the previous example. Total time from the mid air until impact with terrain: Estimated 1 minute 5 seconds.

Each of these scenarios assume that even if there were parachutes on board and people were able to don them correctly in time, that they would be able to use them to survive. Here are a few additional factors that would come into play in the unlikely event that they were able to even get to this point:

  • Many modern aircraft doors can not be opened in flight.
  • If this happened at high altitudes, everybody would need oxygen as well or they would pass out.
  • The passengers that actually make it out of the airplane do not know how to fall in a stable position, and the parachute is very likely to become tangled while opening as they are tumbling through the air.
  • The passengers would need to actually deploy the parachute manually while most probably in a panicked state of mind.
  • There would be many injuries during landing.
  • Once they did land, they would have no survival gear. This is particularly a problem over the open ocean or in the jungle (where these flights have been).

Considering that even in most accidents the aircraft is still landed in a somewhat stable manner and most people survive, having a couple hundred people bailing out of an aircraft would most likely cause more harm than good, even if they could solve all of the technical issues. If the decision is made to evacuate and then the pilots get the aircraft back under control, it would be even worse!

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I'm no expert, but don't your times also skip minimum altitude required for the 'chute to open? –  Allen Gould Mar 12 at 21:12
@AllenGould Absolutely, but you really only need a few seconds for an emergency parachute to open. My point is that even if you had all of that time available, it still wouldn't do any good. :) –  Lnafziger Mar 12 at 21:15
Also, the problems with AF447 started when they flew into a thunderstorm. Jumping out into one of those would probably introduce even more problems to the equation. –  David Richerby Mar 12 at 21:41
You could possibly add the 1996 collision near Delhi to this list: the Ilyushin seems to have stayed airborne and intact for a little while. –  David Richerby Mar 12 at 22:47
Another example is the "Miracle on the Hudson" USAir 1549. They were in stable flight and possibly had enough time to don parachutes and exit (4 minutes after bird strike, much less after deciding teterboro was unreachable), but were not high enough to deploy (as it briefly reached ~3000 feet). –  Ed Griebel Mar 13 at 19:33

Almost all fatal accidents happen during take-off or landing, where parachutes would not be of any help.

If the accident happens at a higher altitude, and the aircraft is still more ore less flyable, it is much less risky to attempt an emergency landing and save most or all of the passengers, than risk parachuting them (the other answers have plenty of reasons why it's risky). If the aircraft can't maintain speed and altitude, you don't have the time to parachute even cooperating passengers, much less panicked ones.

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Using a parachute is not a easy job. It require large amount of training, even well trained army para units face more casualties during para jumping. The key odds for using parachute in a commercial airline are

  1. Untrained personal using a parachute is much more risky and it may not serve the purpose of saving the life. We may not expect all the passengers of a commercial airliner to have attended a para jumping trainings.
  2. Jumping from an airliner at higher altitude requires supplemental oxygen and requires special training.
  3. Cost of a parachute is much higher. So, this would increase the cost of ticket and the benefit out of it is significantly limited. This would not be economically possible.
  4. The parachutes need to be maintained periodically. Maintaining few hundred parachutes per aircraft would increase the ideal time of the aircraft which leads to cost overruns.
  5. It would be literally impossible for children’s, peoples with disabilities to use the parachutes.
  6. Opening a pressurized cabin at a higher altitude would result in a decrease in altitude due to heavy inflow of air and would make the situation even worse.
  7. Parachute jumping needs a stable platform and a steady aircraft. But, in a commercial airliner which is in dangerous conditions it is practically impossible.
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And don't forget that parachutes are pretty much useless to people of over about 200lbs, which is a pretty large part of the adult male western population. They'd either need to be banned from flying or have to sign waivers, which isn't good marketing, and that for no benefit whatsoever. –  jwenting Mar 12 at 10:11
@jwenting Any sources on the 200lbs assertion? –  kmort Mar 12 at 13:10
@jwenting Seconding kmort's request. Paratroopers carry large amounts of supplies (food, weapons, ammo, etc) when they drop; I'd be shocked if most aren't well over the 200 lbs level. My assumption would be that the 200lbs figure is a safety limit for a standard size commercial chute. I also believe the paratroops fall faster and land harder than is normal for recreational jumping; which implies that (at the risk of more injuries from bad landings) there is a decent margin between commercial safety thresholds and going splat. –  Dan Neely Mar 12 at 13:20
@jwenting The US Army uses parachutes that can cope with 360lbs (according to Wikipedia). Perhaps the 200lb limit for jump lessons is because they're tandem jumps at first? –  David Richerby Mar 12 at 17:35
@jwenting I've seen 240 lb. offered as the limit for recreational skydiving, which would include a much larger percentage of the population than 200 lb., though it would still leave out quite a large number of people. –  reirab Mar 12 at 19:48

The profit in aviation in 2013 was about \$11.7 billion, on \$708 billion revenues. So the profit margin in global aviation last year was about 1.6%. How do you expect that to work when you remove about 10% of the fare-paying passengers by replacing them with 8-10kg parachutes?

That is about \$70.8 billion you lose there, every year. Assuming it would save 240 lives every five years (I am being optimistic here), that's about \$1.5 billion per life saved. If you have that amount of money to invest, I can think of more efficient ways to make aviation safer than by adding parachutes which might help in a crash once every five to ten years.

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to be fair, it wouldn't be 10% of paying costumers, it would be 10% of potential customers, the real number would be lower. But even if the number is reduced by half, your point still stands. –  user606723 Mar 12 at 19:00
I disagree with your point. The cost could be recouped by a 10% increase in airfare if this is implemented across the board. –  Question Overflow Mar 13 at 12:42
@QuestionOverflow You miss the point; the costs do outweigh the benefits by far, it is a waste of money. –  DeltaLima Mar 13 at 20:49

There are several good answers above, but another important thing to consider is that it's impossible to jump out of a commercial airliner (except the 727, which is rarely still found in passenger aviation) while in flight, unless a hole has opened in the fuselage or it has otherwise become depressurized. The doors have to be pulled in to open, which is, for all practical purposes, impossible while the airframe is pressurized. From a safety perspective, the additional risk of allowing the doors to open in flight far outweighs the potential benefit of letting people bail out in the narrow range of circumstances that that would even be possible. This is because it would require the doors to open outward, which opens up the possibility of them blowing out in flight. Back when airplanes were designed that way, several people died from explosive decompression due to a door blowing out. This was a problem both on the DC-10 and on early 747s.

A further issue to consider is the locations of the exits. The reason that it was possible to bail from a 727 is that it had an exit in the tail cone. No other passenger aircraft that I'm aware of has that. Many military cargo planes (like the C-130 you mentioned) do use ramps in the tail, though, and that's where people jump out from in those aircraft. If you try to jump from a side door in a jetliner (which are the only doors that exist in most modern jetliners,) you'll likely be promptly cut in half by the horizontal stabilizers moving through you at 550 mph immediately after stepping out the door. Of course, this would also damage the horizontal stabilizer, which would then quite likely result in the death of everyone still on the plane, due to loss of pitch authority. Of course, if you jump out of a door in front of the wings, you might be killed by a wing or an engine rather than a horizontal stabilizer, but the results are still equally undesirable. Jumping out of side doors is possible (and normal) for the much slower aircraft used for skydiving, but not for a passenger jet moving 550 mph.

I don't have time at the moment to run all of the numbers, but one thing did come to mind that helps in the comparison: terminal velocity. Terminal velocity is the point at which the upward drag on a falling object is equal to the downward gravitational force and, thus, downward acceleration due to gravity stops. Where this provides some insight on this question is in the comparison of forces. Terminal velocity for a human is about 120 mph at low altitude. This means that the wind speed required to equal the gravitational force is approximately 120 mph at low altitude (of course, this can vary depending on the shape and mass of the person in question and their position relative to the airflow.) Since drag is proportional to the square of velocity and linearly proportional to air density, this means that a 550 mph wind at an altitude where air density was roughly $\frac13$ of at the surface would exert a force with a magnitude of about $(\frac{550}{120})^2(\frac13)\approx7$ times the magnitude of the gravitational force. So, at least initially, you'd be accelerated backwards about 7 times as quickly as you'd be accelerated downwards by gravity in these conditions. Aside from the fact that being accelerated backwards at around 7 Gs is going to hurt, there is a very real possibility of hitting any part of the aircraft that happens to be behind you. Also, as mentioned in a comment below, it would actually be entirely possible to be accelerated upwards (at least briefly) with that much drag, depending on the average angle at which your body is deflecting the wind stream. Another consideration is that the windstream itself will be faster than the true airspeed of the aircraft itself around certain parts of the aircraft, including around the fuselage and above and behind the wings. Furthermore, the airstream is not always exactly parallel with the aircraft. It can have an upward component relative to the aircraft around certain parts of the airframe while it almost always has a downward component relative to the aircraft behind the trailing edge of the wings. Also, if the plane itself is descending, there will be an upward component of the airstream relative to the aircraft at almost all points, except maybe right behind the wings. So, long story short, a lot of factors play into this, but things aren't looking up for the prospective jumper.

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Pretty much your entire second paragraph is wrong because you are also moving forward at 550 mph and when you jump out you start to drop away kind in a manner similar to a bullet trajectory.... –  Lnafziger Mar 12 at 19:47
Yes, but you fall very very quickly as well. As a skydiver and pilot I can assure you that even when I have edited out of a side door and jumped and stretched and reached for the tail of the airplane, I never even came close because of the physics involved. :-) –  Lnafziger Mar 12 at 19:53
Have you? :-) You are making claims that I find hard to believe, if you have references that prove them then I'd love to hear what you have to say. –  Lnafziger Mar 12 at 20:14
Actually you can jump out of the side of C-130 on static lines. It is done all the time. –  staticx Mar 13 at 12:15
@reirab: when a passenger plane is doing 550mph true airspeed, it is because it is at a height where the atmosphere is about a third as dense compared to sea level. If you would look at the speedometer at that moment, it would show about half that speed. Most aerodynamic characteristics depend on the indicated air speed, not the real one. Bottom line, you should use about half the speed in your calculations. –  Martin Argerami Mar 14 at 5:32

From basic high school physics, assume someone is 1.7m tall and steps out the plane rather than 'diving'.

The equation:


And substituting:


The panicked passenger would take 0.59 s for his head to be safely clear of any decapitating wires that happen to be level with the bottom of the door. If he immediately decelerated to 0 mph forward motion (I need someone else to figure out that part) he goes backwards 130 meters before he has dropped to safety. But even if it takes him 0.4 s to decelerate, that still leaves 0.19 s stationary in relation to the plane when his head isn't safe. That is about 42 meters, not counting the distance traveled while he is slowing down during those 0.4 s so I'm inclined to support @reirab on this one.

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The terminal velocity of a human oriented perpendicular to the relative wind and spread out is somewhere in the neighborhood of 120 mph, so you might figure your worst case deceleration to use this forward speed and assume it happens instantly. –  casey Mar 13 at 4:10
It turns out to be a lot more complicated than this because both the direction and magnitude of drag depends enormously on how your body is positioned relative to the airstream and because the airstream itself might not be exactly parallel to the aircraft depending on your jump location (it would be moving upwards over the leading edge of the wing and downwards aft of the trailing edge,) but this is good as a first approximation. Thanks. And, just to state the obvious, if you're exiting from behind the wing, you are within 40 m horizontally of the horizontal stabilizer on any current jetliner. –  reirab Mar 13 at 12:11
Is there a good reason why you choose 0.4s as the time it takes to decelerate and not 1s or even 5s? –  Question Overflow Mar 13 at 12:46
@QuestionOverflow, Based on my computations above from the drag equation, the initial acceleration due to drag would have a magnitude about 7x the acceleration due to gravity. 1 g = about 32.17 ft/s^2, so 7 gs is about 225 ft/s^2. If we used the above equation for a constant acceleration, that would give us a backwards displacement of 39 ft in the 0.59s it takes for your head to drop below the level of the bottom of the exit door. The real displacement in the first 0.59s would be a bit less since the acceleration isn't constant (requires a diff eq to get the exact answer.) –  reirab Mar 14 at 15:28
However, the drop required to really be safe would depend largely on which door you exited from, the type of aircraft, and the attitude of the aircraft relative to the airstream. If you jump in front of the wing, you'd need to fall further to be safe in a normal commercial aircraft, since the bottom of the wing is usually well below the cabin exit doors. If you exit behind the wing, the distance you need to fall will depend on the position of the horizontal stabilizers and the attitude of the aircraft relative to the airstream, both of which can vary significantly. –  reirab Mar 14 at 15:33

Prelude: While studying for being airplane engine engineer in university I took 3 years of special military course where been taught to be military aircraft mechanic. Also forgive my possible incorrect tech terms as English isn't my native language.

While here are plenty of great answers about parachutes with detailed explanations and facts about it, I'd like to add my 2 cents about emergency ejection systems.

As OP has stated one on hand those systems are expensive, but this isn't the main point why those are not used in commercial aviation. There are two points to consider:

  1. Those systems are heavy. We all have seen how on commercial airlines they weigh your luggage. This is done for a reason - the airplane does not have infinite weigh capacity. If we equip standard commercial plane like Boeing 777 with eject seats there will be no free weight capacity for either passengers or their luggage. One such system (the one I have studied) weights appx 80-90 kg. Seeing standard commercial seats I'd say their weight is no more than 10-15 kg (anyone correct me if I am wrong here). However installing such systems could be done for example on private airplanes where the number of passengers is limited and thus there is some free weight capacity, but it still would be bad solution due to second point.
  2. In order to survive ejection procedure one should have perfect health and wear special suit. Let's start from suite - you've probably seen in movies that military pilots wear special suits, those suits are designed to handle two things that happen to you during flight - depressurization and extreme acceleration. Not sure if in any movie it was shown, but this suite actually consists of network of tubes and pads that are being inflated with high pressure air through connection in pilots seat. Why there is a need in such suit? I won't talk about normal flight in those suits as we are talking about commercial airline, let's see what happens during ejection. When one is ejected, their seat is basically being launched with a rocket engine, in order to prevent damage to pilot/passenger from any parts of aircraft, he/she should be moved away of it very quickly, this means very high acceleration rate. On the other hand our body contains big amount of liquids. Now imagine what would happen if suddenly kick a glass with water? Inertia will hold liquids from moving together with glass, that means all blood in case of ejection will move down in our body - 1) leaving our brain without oxygen supply; 2) destroying blood circulation systems in bottom half of our body. With special suit (that with extra pressure on our body balances this effect) we can make sure that our body will not burst itself out with high pressure blood from below chest level. Although I myself never went through such examination, while studying we learnt that one of very important health checkups for pilots is their cardiac system, means that their heart and blood tubes will be able to handle such an extreme procedure (and this is why running is an important part of military training as it strengthens whole blood circulation system). Still having said all of that about military pilots, more than half of them while will survive ejection procedure, will blackout for some time due to low oxygen level in brain. Also as we were told while studying, even with all this training and equipment people who once went through ejection in mid-air are usually not piloting after that due to damages their body suffered (this info maybe outdated as eqipment we learnt was about 10 years old at that time). Now compare trained military aviation pilot equipped with compensation suit to the average commercial airline passenger who perhaps smokes, eats high cholesterol food and doesn't do much sports ;) What do you think will be chances of survival?
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The technical answers have been great, but there is one very simple answer to why airlines don't provide parachutes:

It implies that commercial flight isn't safe

For the similar reason that car's don't protect you to the nth degree, many people will stop using them as they'll realise just what they are actually doing, and as pointed out in another answer the margins are so low that a 10% drop in passengers would be ruinous to many airlines.

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I don't agree that adding safety measures implies that something is not safe. They do provide emergency slides and life vests. Isn't that basically in the same category? –  DeltaLima Mar 15 at 10:16
No of course not. Telling my wife that is some situations she may need to put life jackets on herself and two kids snd slide down an inflatable slide to ground or water is one thing. Saying there's a chance she may need to get them into parachutes and jump out with them as a plane hurtles to the ground is another, having parachutes reminds them constantly that this may happen, and many will start to think twice. –  The Wandering Dev Manager Mar 15 at 10:25
By that argument, car sales should have dipped after airbags became standard. –  David Richerby Mar 17 at 1:39
No, there is no similarity. The point isn't adding safety features (airbags are a balloon in most people's eyes), it's reminding people that they are miles up at high speeds and their safety/existence is totally reliant on the metal tube they are in. Many people don't want to think about that. A better analogy would have been to offer parachutes in skyscrapers in case of 9/11 style attacks, many would think twice about going to high floors. –  The Wandering Dev Manager Mar 17 at 6:34

As an alternate answer in that you can still get parachutes on a plane, even if the airline doesn't provide them...we had a related question over on Travel.Stackexchange. While, as you noted, airlines don't typically provide parachutes, the TSA specifically allows you to bring your own.

Are parachutes allowed on airplanes as cabin baggage?

Short version from the TSA:

You may bring skydiving rigs with and without Automatic Activation Devices (AAD) as carry-on or checked luggage.

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This Incident is not well known so I would like to add Philippine Airlines Flight 812 also (see ASN) to this Question. Technically it is possible referring to this Incident.

The hijacker demanded the passengers place their valuables in a bag before he commanded the pilot to descend and depressurize the aircraft so that he could escape by a homemade parachute.

Three days after the hijacking, the hijacker was found dead, his body nearly buried in the mud, in the village of Llabac, in Real, Quezon, about 70 kilometers southeast of Manila, near the border with Laguna province. It is speculated that he survived the fall but was killed by the mud

Edit because of constructive comment: Of course this Incident shows that many factors like depressurizing the aircraft and low flightlevel is needed. And as kangacHASHam mentioned, the factor that you can be hit by the tail is quite high.

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This does not really answer the question. while showing that a single person might jump, does not constitute evidence that all the passengers and crew might escape safely if needed. –  Federico yesterday

protected by Community Mar 16 at 17:08

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