You've got to be in dire straits to attempt to stowaway on an airplane—hiding in the wheel well of a jetliner is one of the most obviously dangerous things you could possibly do. Will hiding outside the pressurized environment of an airplane's cabin kill you?

The answer should absolutely be "yes." According to what we know about science, the human body should not be able to survive the temperatures and lack of oxygen at cruising altitudes.

Nonetheless, stowaways do survive from time to time: Thursday, a man was found alive after hiding in a British Airways flight on an 11-hour flight from Johannesburg to Heathrow. A second man, however, was found dead on the roof of a building in Richmond, England—he's believed to have also attempted the trip.

The most common (and perhaps only) method of stowing away on a flight is to sneak onto the runway while a plane is stationary and to climb the wheels of the plane into the wheel well. According to a Federal Aviation Administration study from 1996, "certain aircraft contain sufficient space in the landing gear area for a small adult to crawl into the space and hide relatively securely."

"Of those 113 attempts, 76 percent of them were fatal"

"The vignette that generally describes the known cases involves the individuals hiding near the point where the departing aircraft waited at the runway for take-off clearance," according to the paper. "While the aircraft was stationary, the stowaways mounted, undetected, a main landing gear and climbed into a wing recess area adjacent to where the gear would retract."

In that sense, the idea of "clinging" to the wheels or outside of a plane for hours is incorrect—when the wheels retract, you are, more or less, secure inside the body of the aircraft.

"That approximately 24 percent have survived highlights some lesser known aspects of human tolerance for extreme conditions"

That does not mean this is even a remotely safe activity. Between 1947 and 2015, the Federal Aviation Administration has recorded 113 attempts to stowaway on 101 flights (in some cases, people stowaway together) originating in or landing in the United States, according to numbers tallied Friday for Motherboard. Of those 113 attempts, 76 percent of them were fatal. Just 27 people have survived, 86 have died.

These numbers are probably quite low—as the 1996 paper notes, "some successful stowaway flights may be unknown," whereas many other people have probably fallen "into the ocean or into a remote land area," never to be seen or heard from again. It's grim stuff.

An FAA investigation recreated the conditions of a stowaway scenario. Image: FAA

"The environmental and physiological conditions that such stowaways face should, particularly in the higher altitude exposures, lead to almost certain death for the stowaways," Roland Herwig, an FAA spokesperson, told me. "That approximately 24 percent have survived highlights some lesser known aspects of human tolerance for extreme conditions."

Let's look at these extreme conditions. According to the 1996 paper (very few actual studies have been done on the subject—outside of a case study here or there, it appears to be the only real academic look at the science of stowing away), there are a variety of reasons why someone might die stowing away.

Wheel wells of airplanes aren't pressurized, meaning that as the plane ascends, oxygen levels decrease, as do temperatures. At cruising altitude, ambient temperatures reach as low as -81 degrees F. It's slightly more complicated than that, however.

"Accompanying the climb is some friction heat generated within the tired during take-off that can radiate to the stowaway. Also, due to the warm hydraulic fluid in the lines within the wheel-well compartment, some additional radiant and conductive heat is present in the stowaway area," Stephen Veronneau, a coauthor on the 1996 paper, wrote. "These heat sources are progressively diminished as flight at altitude proceeds."

"Survival is jeopardized if the recovering stowaway begins moving round and falls out when the landing gear is lowered"

Some people have died of hypothermia while stowing away; others have literally frozen. Even those who survive rarely make it out unscathed.

"Survivors often have some medical sequelae such as hearing loss, tinnitus, and frostbite injuries," Herwig told me.

Other risks worth mentioning are decompression sickness, which is often suffered by scuba divers and comes from rapidly changing pressure environments, and that of a nitrogen gas embolism—a bubble of nitrogen gas that can give you a heart attack or a stroke.

Even if you don't freeze to death or suffer one of those terrible fates, you will certainly lose consciousness during the flight—according to Veronneau, it's impossible to stowaway without passing out at some point. In such awful conditions, this actually sounds ideal, except it highly increases the chances of you falling to your death when the plane goes to land.

"If the individual is so fortunate as to avoid brain damage or death from the hypoxia and hypothermia, cardiac arrest or failure on rewarming, or severe neuromuscular complications, some progressive recovery of consciousness occurs," he wrote. "Survival is jeopardized if the recovering stowaway begins moving round and falls out when the landing gear is lowered."

From a cursory look at some recent cases, it appears as though many people do indeed end up falling out of the plane. Oddly enough, one of the papers I found on the subject said that a man found dead in Miami in the 1990s was suspected to have been hit by a car, but upon further forensic review, it was determined he fell out of an airplane.

Given all these terrible outcomes, how is it possible that anyone ever survives? Veronneau has some theories. He suggests that temperatures become so cold so fast that the bodies of those who survive enter what's known as a "poikilothermic" state, which is reminiscent of hibernation. Poikilothermic bodies don't have as great a need for oxygen as "unconsciousness, and lower heart and respiratory rates occur."

Not many more clues are given. I couldn't reach Veronneau for a proper interview, but he mentioned that "a youthful, thin, non-exercising individual is less likely to experience decompression sickness than are heavy-set and older individuals." He also reported that most stowaways are "lightly clad," meaning they lose body heat more rapidly.

Stowing away seems like an awful experience, whether you live or die. So why do people do it? Veronneau notes that in incident reports, survivors say they are often political refugees hoping to "escape the living circumstances in their home country." Indeed, most stowaways appear to be on flights leaving politically unstable countries for western Europe or the United States.

It's clear very few people hide on a plane for the hell of it, but if you are thinking about it, stowing away on a plane will almost certainly kill you.