Air Safety Link
By Jan W. Steenblik, Technical Editor
Air Line Pilot, September 2003, p. 5
Capt. Louis Dashiell (Atlantic Coast) was frustrated: The damned pegs wouldn’t go into the holes. Well, if they weren’t going to cooperate, screw ’em. Each time a peg didn’t fit in the hole, he’d chuck it into the near corner of the altitude chamber.
Maybe not the kind of reaction to frustration you’d look for in an air-line pilot—but he couldn’t help it. He’d been off the mask for a few minutes, at a pressure altitude of 25,000 feet, and his brain cells were slowly dying.
It was, as they say, a learning experience.
That was the whole point of the condensed course in hypoxia, complete with a ride in an altitude chamber, that several of the participants in ALPA’s Advanced Accident Investigation Course took after their own course was completed.
Dr. Warren Jensen, board-certified in aerospace medicine and an associate professor at the UND Aerospace Foundation, made the learning experience available to the ALPA students.
For some with military backgrounds, the experience was a valuable refresher; for those with civilian-only flight training, Dr. Jensen’s lecture and the altitude chamber ride were a unique opportunity.
One of the goals of aviation medicine, Dr. Jensen explained, is to "help people optimize performance in hostile environments. And when you’re at altitude, outside your window is an environment in which you cannot survive. It’s a very hostile, lethal environment.
"Space," he continued, "to a scientist is 1,200 miles up; to a pilot, it’s anything about 50,000 feet. Between 10,000 feet and 50,000 feet, the partial pressure of oxygen is the currency by which you live or die. It doesn’t matter how tough or mean or smart you are, or what your grade point average is."
Demonstrating why he has twice been honored with teaching awards by the UND student body, Dr. Jensen succinctly covered the subject of hypoxia from a pilot’s perspective.
Hypoxia, which impairs intellectual function, is characterized by insidious onset, and the onset rate depends on several variables—e.g., individual tolerance, physical fit-ness (including smoking), rate of ascent, environmental temperature, duration of exposure, psychological factors, physical activity, and altitude itself. The human tissues most sensitive to hypoxia are the retina and the brain.
Effective performance time—sometimes called "time of useful consciousness" at a particular pressure altitude—drops off dramatically as pressure altitude increases. For example, at FL180, most people will have 20–30 minutes to act; at FL350, this drops to 30-60 seconds.
"At FL430 and higher," Dr. Jensen warned, "you only have 9-12 seconds. In the case of rapid de-compression, it will take you at least 6 seconds to detect and recognize the decompression, then decide what to do and act on it. At higher altitudes, you absolutely must get your emergency oxygen mask on immediately after rapid decompression."
Subjective symptoms of hypoxia can include "air hunger," headache, nausea, hot and cold flashes, euphoria, tingling, apprehension, dizziness, fatigue, blurred vision, tunnel vision, and numbness. The objective signs include mental confusion, increase in rate and depth of breathing, cyanosis, belligerence, poor judgment, loss of muscle coordination, euphoria, and unconsciousness.
"It’s the subtle things I want you to see," Dr. Jensen explained.
In the altitude chamber, which the UND Aerospace Foundation rescued from a U.S. Air Force junk-yard and refurbished, Joe Schalk, manager, and George Lamora, lecturer, from the UND Aerospace Foundation’s Aerospace Physiology program, helped their charges learn how to operate their individual oxygen consoles. The pilots spent 30 minutes breathing pure aviation oxygen at ground level to purge dissolved nitrogen from their tissues and prevent "the bends" (decompression sickness).
Then Dr. Jensen took the pilots quickly to 30,000 feet, where First Officer Don Del Carmen (Hawaiian) volunteered to be the subject for the first hypoxia demo. When F/O Del Carmen—a DC-10 pilot and mellow surfer dude—began the classic hypoxia exercise of putting plastic pegs in the board designed to receive their different cross-sectional shapes, his ever-present, easy smile gave no clue that he was losing his ability to think clearly. With every breath, his body was exporting oxygen, but the performance results were subtle—until he just couldn’t muddle through any more.
"I think you’d better put your mask back on," said George Lamora, helping him with the fittings.
Descending to FL250, the pilots took turns watching each other go through various activities while off the mask.
This is one of those aviation experiences you can read about, be lectured about, flirt with a little when you’re flying a non-pressurized airplane for the legal 30 minutes between 12,500 and 14,000 feet, but never fully appreciate until you go through the real deal. Aviate, navigate, communicate? Forget it!
Print out "HYPOXIA HELPS IMPROVE MY HANDWRITING" several times while you’re off the mask, and pretty soon those beautiful block letters you were so proud of in mechanical drawing class years ago have turned to a barely legible "HYPOXA HELPS INPROVE MY HAMDWRIITING."
Capt. Ray Gelinas (Air Canada Jazz) did a great job of peeling playing cards off a deck, one at a time, reading the suit and number out loud, then holding up the card for everyone to see. A great job—right up until the moment his hypoxic mind froze, and every subsequent card was the three of spades. At least, that’s what he thought.
One participant noted a major change in his hypoxic symptoms since his one previous chamber ride in 1975, courtesy the U.S. Navy. Then, when he was 26 years old, hypoxia turned him into a happy drunk; the failure of the pegs to fit the holes was the funniest thing that had ever happened in the history of the universe. In the UND chamber, at age 54, hypoxia gave him tingly hot flashes and a touch of anxiety, then lethargy leading to sleep.
Back in the classroom after the chamber ride, the ALPA representatives compared notes. Every one could say, without qualification, that Dr. Jensen was right when he warned, "With hypoxia, you’ve got to have a low threshold of suspicion."