Daybreak on Monday brought a surprising story of survival with news that a teenage stowaway miraculously survived in the wheel well of an airplane after a six hour flight from San Jose, California to Maui, Hawaii this weekend. The story is notable because the vast majority of airplane stowaways die long before the aircraft reaches its final destination.

Stowaways hide out in the most easily-accessible part of an airplane to someone running across the tarmac — the landing gear bay, or wheel well. Airplanes are pressurized for your survival (not for your "comfort," as they like to say), but the wheel well doesn't benefit from this pressurization, so the folks trying to hitch a ride usually wind up dying in the process.

The reason behind airplane stowaway deaths comes down to the basic structure of the atmosphere.

1) Most Air Is Near the Ground

Air in the atmosphere is not evenly distributed. The troposphere — the lowest level of Earth's atmosphere — is only 5-10 miles deep but contains 80% of the total volume of all of the gases in the atmosphere. A huge amount of the troposphere is again condensed to the first few miles above the earth's surface.

This principle is displayed by the Skew-T/Log-P charts that meteorologists use to graph observations recorded by weather balloons. Air pressure in the atmosphere drops logarithmically with height; in other words, air pressure starts dropping extremely fast the higher you get off the earth's surface.

On the Skew-T chart above, I've highlighted each of the pressure levels in the atmosphere. Standard air pressure at sea level is 1013 millibars, and the jet stream is typically located between 200-300 millibars.

Airplanes flying on long-haul routes (such as the California-Hawaii route in question) routinely fly as high as 36,000 feet. In the chart I posted above, 36,000 feet would correspond to about 225 millibars, a level at which the amount of oxygen is well below what humans need to survive. In fact, most stowaways would suffocate and die even before reaching cruising altitude. There's just not enough oxygen in the upper-atmosphere to survive.

2) It's Really, Really Cold

The weather balloon sounding over Oakland, California last night (shown in the Skew-T chart I used as an example above) recorded temperatures of almost -60°C (-76°F) at 36,000 feet. At these extremely low temperatures, exposed skin will experience frostbite in just a few minutes, and one's body temperature would quickly drop until hypothermia (and eventually death) set in.

These are the two main factors that contribute to almost all deaths in people who try to hitch a ride in an airplane's landing gear bay. If the lack of oxygen doesn't kill them, the cold usually does. But like the 16-year-old boy from California this weekend, some of them manage to survive against all odds.

Even if a stowaway manages to survive the harsh atmosphere, there is one more hurdle they have to make it through to arrive alive.

3) It's Not the Fall...

Another particularly gruesome fact about stashing away in the wheel well of an airplane is that some stowaways fall out once the pilots extend the landing gear when the aircraft is on final approach.

If you're not familiar with how the landing gear on commercial aircraft operate, the above photo shows the landing gear of a Boeing 777 aircraft. When they're retracted, the wheels fold up into landing gear bays that are closed off by a door. When the pilots extend the landing gear, the bay doors swing open and the landing gear extends into position.

When the bay doors open, the deceased body of the stowaway can fall out of the airplane if it's resting in the wrong location. The bodies of stowaways falling from airplanes on final approach has happened a few times in recent history, including on flights from Angola to London and from Charlotte, N.C. to Boston. The FAA lists several instances where a stowaway managed to survive the extreme temperatures with little oxygen, only to fall to his or her death when the airplane started to land.

People stowing away in the wheel well of aircraft have to be incredibly desperate (and incredibly uneducated) to attempt such a lethal feat. The BBC lists dozens upon dozens of cases in recent years where stowaways were found on (or left behind by) aircraft around the world, and over three-quarters of them died in the process. Stowing away is incredibly risky and often not worth the outcome.

[Images: AP / U. of Wyoming (with annotations by author) / Oliver Cabaret via Flickr]