Firstly, it is important to note it is rather unlikely you will find your self in an aircraft that will cause the death of you¹ or a fellow passenger². However if you happen to be unfortunate enough to be on board an aircraft that has either lost control in the air, or has chose to meet the ground in a less than amiable fashion (known in the industry as "controlled flight into or towards terrain"), you have very few options. There is, of course, the possibility that you aircraft will, at the last possible moment, recover from whatever catastrophe had befallen it and fly off into the sunset, but we shall assume this is not the case, and your aircraft, with you aboard, will continue plummeting towards Earth. As previously mentioned, you have few options, and fewer that result in survival, but you have to start somewhere, in which case:

Don’t Panic!

As it is likely you will not survive ³, so you might as well keep your head, and, if possible, eat a light snack to qualm your stomach, which is likely churning with anxiety⁴. Now that you’ve come to grips with your situation, realize that you are likely on the path to your eminent demise. But fear not! There is a slight possibility you will survive the impending crash, and if not, rest easy in the knowledge that your relatives will be able to cash out that large life insurance policy you recently took out. Regardless, you have two choices available to you:

1. Leap out the door and chock your survival up to your free-fall/flight skills, or
2. Stay in the aircraft, and get to know the person sitting next you, as they may very well be the last person you will ever see.

Option 1: Learn to Fly

If you just can’t take any more of the wailing, mewling, or screaming cacophony put on by the rest of the passengers, this is the choice for you. Although it is unlikely you will be able to open the cabin door (thanks to modern technology and Daniel Bernoulli⁵), assuming you are able to find a way out of the aircraft, and don't smack into the wing or tail of the aircraft on the way out, you are now free to quibble with gravity over if, when, and where you are going to die, without relying on some two-bit pilot and a set of unreliable aluminum wings. If you happen to have a parachute, now would be the time to use it. If not, see How to Survive Falling out of a Plane.

If You're the Indecisive Type...

If you're not sure you want to go through the trouble of finding the door:

• Jumping out of the aircraft at the last minute will most definitely NOT help: you will quickly reach terminal velocity, and things will be no different than if you abandoned ship at 30,000-ft. Unless you've flown over a soft patch of snow, peat, whathaveyou, you'll run into the same troubles outlined in the aforementioned article, minus the benefit of a great view.
• The benefit of staying in the plane is that, upon hitting the ground or body of water, the aircraft absorbs most of the impact, rather than your rib cage. This is along the same line of thought as the crumple zones in cars.

Option 2: Falling with Style

If your plane is no longer blessed with a wing, a tail, or a large section of the fuselage⁶, this choice is most certainly fatal, but it it is likely your only option, due to the careening nature of the aircraft. If you are lucky enough to have all the major flight components, your aircraft will be in a glorified state of falling known as gliding, and depending on your aircraft and the skills of your pilot, you will have a maximum of five minutes before you really want to be buckled in. The stewardesses, of course, will implore you to remain seated at all times, but while this could well be your last five minutes above the earth, if you must take a trip to the lavatory, now would be the time to do so (in a TIMELY FASHION, mind you). If you are told to put on an oxygen mask, do so.

Once you are securely buckled in your seat, place your hands on the top of the headrest in front of you, your head between your arms, and prepare for landing. During this time, think back on your life on the earth, pray to whichever deity you deem necessary, or start up a conversation with the person sitting next to you. Recommended topics include the weather; the current political situation; or how long the lines were going through security, and discuss how if the lines had just been a bit longer...

Alternatively, scream. An oxygen mask will make this more difficult, but do your best. If you have an overwhelming desire to panic, now would be a good time to do so, provided you stay seated.

If these recommendations on how cope with your upcoming dance with mortality do not strike your fancy, check here for more options.

Out of Your Hands

Ultimately, your survival is dependent on the skill of the pilot, the structural state of your aircraft, the terrain/body of water where you end up landing, what seat that internet booking service gave you, and how lucky you happen to be that day. If you have recently won the lottery, pray that you have enough latent karma to offset all that good luck you recently used up. By and large, there is little you can do to alter your current collision course with death, but there are a few things you can do to help your (slim) chances:

• Pay attention during the pre-flight safety briefing

Though few people enjoy watching this pantomime, doing so may alert you to the proper way to don your oxygen mask, as well as use your seat cushion as a flotation device.

• Read the safety data card provided to you

Fewer people read this than enjoy the briefing, but doing so increases your chances of survival ever so slightly, according to the FAA's Advisory Circular ⁷. Knowing where your exits are, how to unbuckle that confounded seatbelt, and how to correctly fold yourself into the brace position all add that potentially crucial 2% to your survival chances. Also, make sure your fellow passengers have both payed attention to the safety briefing and read the data card, as your calm evacuation can be stymied by the trampling herd that is the rest of the passengers.

• Stay seated with your seat belt fastened

Most in-flight injuries are related to passengers' seat belts not being fastened. If you are intent on surviving, consider abstaining from that pre-crash lavatory visit. Additionally, position yourself in the currently popular brace position, as outlined by the safety data card. As awkward as it may be, it can be shown that such a bodily contortion can greatly increase your chances of survival (say, 10% to 13%).

• Wear comfortable, natural fiber, long sleeve clothing, and close-toed shoes

Natural fibers, such as cotton, will hold up better to high temperatures in the event of a fire, and long clothes, as well as close-toed shoes, will help to protect you from any sharp debris you may encounter during a crash and any subsequent evacuation.

• Sit near the rear of the aircraft.

Assuming you are able to use a seat and a seat belt. Despite what the FAA says, you can be up to 40% more likely to survive a crash by sitting in the back of the aircraft.

Success!

So, you survived the crash!!! Congratulations, but now you must escape the twisted, smoking hulk of a downed airliner (or the crinkled, sinking wreck, depending on where you landed). First off, thank your lucky stars you've survived thus far, but don’t whip out the 3 fluid ounces of scotch you had stowed away just yet. If your pilot was skilled enough, and you landed in a flat field, you may still have unbroken and fully functional legs. Using these to their full potential, calmly move towards the nearest exit, and exit the plane in whatever fashion available. If the inflatable carnival slides are intact, these are your best bet for an injury-free egress. Before committing yourself to the nearest exit, of course, make sure the way is clear of any fire, large debris, or the rare tiger trap. This is crucial: after 'landing,' most aircraft fatalities are due to fire or smoke inhalation, and by knowing where your exits are, and moving towards them calmly, will decrease your exposure to such health hazards. Considering you survived a potentially deadly meeting with tera firma, it would be sorry indeed to die at this point. Hopefully, there have been a few uninjured bystanders who can both call for help, and perhaps jeopardize their own lives to help you and your fellow passengers; in numerous instances, the quick and heroic action by members of the public have saved many lives.

Once you’ve made it out of the wreckage, move far enough away to ensure the plane cannot harm you further, but don't stray too far; any rescue operations will likely zero in on the plane’s carcass, and you don’t want to miss your chance for rescue. Depending on your location, rescue could be a few days away, so be prepared to rough it for a little while: ration any food and water you may have, and search the remains of the aircraft for any useful items once the flames have died down. Useful items include:

• Airline blankets (double as towels)
• Food and/or Water
• Bits of shiny metal or mirrors (for signaling rescuers)
• Medical supplies
• Toilet paper⁸

If you ditched into a body of water, the best you can do is float in the rafts for as long as that package of peanuts holds out (assuming you haven't eaten it already), while if you crashed on land, you may be able to make the best of your impromptu camping trip. For survival tips, see:
How to Survive Extreme Weather
Tips for Camping in the Wilderness
Ten Essentials of Outdoor Survival

and
Finding Your Way Back to Civilization.