December 28, 2010
By Mike Ely and Linda Street-Ely
Mike: Humans are made to live in the physiological efficient zone – from sea level up to 10,000 feet. Flying high in an airliner, you’re sitting in cabin pressure of about 8,000 feet altitude. Without pressurization, at high altitudes hypoxia, decompression sickness, and trapped gases could occur, so a pilot needs to understand physiological hazards associated with that environment, how to mitigate those hazards and deal with them if they happen.
To be pilot-in-command of an aircraft capable of operating above 25,000 feet the pilot must receive and log additional high altitude training, both in classroom and flight (either simulator or aircraft). The ground portion of training covers high altitude aerodynamics, meteorology, the symptoms and effects high altitude sickness, duration of consciousness without oxygen, effects of prolonged use of supplemental oxygen, and other physiological aspects of high altitude flight. Additionally, most pilots also receive training in an altitude chamber, a sealed vessel capable of simulating altitudes much higher than 25,000 feet.
Experience is the best teacher and NASA’s altitude chamber exercise gives the pilot a thorough understanding of the effects of altitude on the body, and to be able to recognize one’s own reaction and symptoms of hypoxia by experiencing hypoxia in a controlled environment.
Linda: My chamber partners were two U.S. Customs and Border Protection pilots/officers. Two NASA trainers joined us inside the chamber. A doctor and three more NASA operatives were outside the chamber along with two observers from the FAA.
The “climb” to Fight Level 250 (25,000 feet) took about 30 minutes. Then the plan was for the Customs guys and me to remove our oxygen masks for a maximum of five minutes. We were to solve math problems and answer other questions during the time our masks were off. I answered the math questions okay in the first minute, signed my name in the three blanks and listed the last five U.S. presidents. During specific time intervals I wrote down my hypoxia symptoms: "Slightly dizzy" began pretty much right away. I wrote "dizzy" after about a minute and a half or so, "dizzier" around two to two-and-a-half minutes, and "rapid heart rate" at about the three minute mark. Before re-donning the mask one of the FAA observers said my fingernails were so blue it looked like I had on nail polish. I hadn’t even noticed.
The mask caused some claustrophobia issues for one chamber mate but he completed the exercise anyway, putting the mask back on after about three minutes. The other made it the full five minutes. Many variables affect a person’s stamina for reduced altitude pressure at any given time. Rest, nutrition, fitness, smoking and alcohol, and overall general health are contributing factors.
My ears didn’t handle the 5,000-foot-per-minute decent well. The valsalva maneuver – pinching my nose and blowing out while swallowing – was unsuccessful for me. I was unable to equalize my ears, so we descended at a slower rate. My Eustachian tubes may be small or scarred from many childhood ear infections. The NASA doctor checked my ears afterward reporting no blood or fluids, but my right ear didn’t equalize for about a week. As uncomfortable as early signs of hypoxia are, I’m glad I experienced NASA’s altitude chamber. Its an extremely valuable tool for learning signs of hypoxia and the importance of avoiding it.