Sparse oxygen, numbing cold present high-altitude perils

Learjet crash sparks interest in pilot training

October 31, 1999|By Robert Little and Marego Athans | Robert Little and Marego Athans,SUN STAFF

Above 40,000 feet in the air, where Payne Stewart's Learjet was flying before it crashed mysteriously last week, even a top athlete would lose consciousness in about 8 seconds and slip into a frozen death, experts say.

Investigators suspect that Stewart's plane lost pressure at high altitude, incapacitating the crew and setting off a four-hour, autopilot ghost flight that ended in a nose-dive crash in South Dakota.

Whatever the cause, aviation experts say, the crash should remind passengers -- who tend to ignore flight attendants' preflight safety demonstrations -- that modern jets are little more than tubes of simulated sea level, flying through a sky so inhospitable that it would kill most humans before they took a second breath.

"They didn't suffer. You just go out so quickly," said Bernice Haydu, a former flight instructor and aircraft dealer from Riviera Beach, Fla., who went through decompression training with the Women Airforce Service Pilots of World War II.

"It would have been instantaneous" at that altitude, she said. "If there's such a thing as a merciful death, that's what it was."

What looks like a bright, sunny day from behind an airplane window is an environment so hostile to the human body that it might as well be at the bottom of the sea. Oxygen is sparse, and the temperature can be 70 below zero.

Airplanes never dared go into such harsh conditions 60 years ago because humans need to stay within about 10,000 feet of sea level to avoid passing out. But since Boeing Co.'s introduction in 1940 of the Stratoliner, the first aircraft with a pressurized cabin, planes have used sealed compartments and forced air to duplicate conditions at 8,000 feet, taking oxygen along for emergencies.

Commercial aircraft typically fly at 35,000 feet, where the air is thinner, friction is diminished and high speeds are possible.

Business jets can reach 50,000 feet or more.

The risks of traveling in such simulated comfort are low. A search through 15 years of accident investigations by the National Transportation Safety Board revealed fewer than a dozen cases in which cabin pressurization contributed to a crash or other accident.

Some longtime pilots think the crash of Stewart's plane will prompt more commercial pilots to seek training in chambers that simulate conditions at high altitude.

Accidents are rare; but when they happen, the danger is immediate, extreme and often deadly.

If a cabin decompresses rapidly because of a blown door or ruptured fuselage, air inside the cabin expands and rushes through the opening, sucking loose objects or people along with it, said Rogers Shaw, who runs pressure-chamber simulations for the Federal Aviation Administration's Civil Aeromedical Institute in Oklahoma City.

Nine passengers were blown out of a United Airlines flight near Hawaii in 1989 when a cargo door blew off and ripped into the passenger compartment. The plane lost pressure at 22,000 feet.

The risk isn't over for those who remain on the plane, aeromedical experts say. Air also expands inside passengers' lungs, blowing out of their mouths and leaving them feeling as if they have just exhaled vigorously. Depending on the altitude, they could have little or no chance of getting oxygen back in.

Humans can't breathe normally at high altitude. The air has the same 20 percent oxygen content it has on the ground, but the molecules are spread farther apart. And because of the reduced gravity and atmospheric pressure, the oxygen has a hard time bonding to the blood's hemoglobin for the trip to the brain.

Because blood cycles from the heart, through the lungs, to the brain and back in about eight seconds, people exposed to conditions above 35,000 feet could be unconscious before they realize what happened.

"All humans go unconscious almost instantly at 32,000 feet, even Olympic athletes," said Dr. Stanley R. Mohler, director of aerospace medicine at the Wright State University School of Medicine in Dayton, Ohio.

"Mountain climbers have made it up to about 29,000 feet, the top of Mount Everest, but they've done it gradually, and if they weren't using supplemental oxygen, then they weren't thinking clearly up there."

A gradual decompression is equally dangerous because it can go unnoticed.

Euphoria is a common effect of oxygen deprivation, so people might ignore other symptoms before it's too late.

Only military pilots are required to train in altitude chambers that let them experience what oxygen starvation, or hypoxia, feels like.

Symptoms include dizziness, nausea, hot and cold flashes, and a tingling sensation that feels like ants crawling on the skin, said Shaw.

"Some people get euphoric; some people get belligerent," he said. "It's like a free six-pack."

Brian Batty experienced hypoxia about five years ago during three training sessions that simulated cabin decompression at 22,000 feet. Within two to four minutes without an oxygen mask, his vision narrowed, he got hot and cold flashes, and his world stopped making sense.

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