March 18, 2014 -- With all the mystery swirling around Malaysia Airlines Flight 370, many people wonder why the passengers and crew didn’t used their cellphones to call or text messages of distress. There’s speculation that the cabin may have lost air pressure for some unknown reason, incapacitating all onboard.
Under ordinary circumstances, most aircraft cabins are pressurized to 8,000 feet above sea level, an altitude that lowers the amount of oxygen in the blood by about 4 percentage points, according to a recent New England Journal of Medicine report. This may lead to some discomfort but no ill health effects for a person in good health.
But if there was an air leak, the plane flew too high or someone intentionally fiddled with the craft in some way, it would have had detrimental effects, said Randy Padfield, a licensed pilot with more than 10,000 of flying experience and the CEO of Aviation International News.
“What happens first is your brain is not as quick. You’d get very confused and stop thinking clearly,” he explained. “Then you’d fall asleep and eventually die due to lack of oxygen.”
Padfield said depressurization can happen quickly or slowly.
If quickly, there is little time to react, although pilots are trained to keep an eye on cabin pressure and adjust the plane’s oxygen levels accordingly. Once pressure dips below acceptable levels, oxygen masks drop down and people put them on to breathe in pure oxygen for as long as it lasts. Protocol dictates that the pilot fly to a lower cruising altitude in an attempt to rebalance the pressure between the air inside the plane and outside the plane.
If depressurization happened slowly, passengers might not notice right away, Padfield said. They might feel woozy and drift into unconsciousness. Anyone with asthma, a heart condition or who is elderly would feel the effects much sooner.
When a cabin depressurizes, the percentage of oxygen in the air stays about the same but the molecules get further and further apart, Padfield explained. “Imagine a balloon at sea level, then take it up to 10,000 feet. The balloon gets bigger because there is less pressure pushing in against it,” he said.
The aircraft’s engines pressurize the cabin with outside air, according to Air and Space magazine. Compressed air gets hotter and hotter as it runs through a series of fans and rotors. Some is diverted to de-ice the wings and the rest goes through a cooling system similar to a car radiator. Then the air expands through an expansion turbine that cools air in the same way you can cool air by blowing it out of puckered lips. Finally, the air goes into a mixer, or manifold, and is recirculated through the cabin with a series of fans.
Padfield said that if a door or window blew out during flight, the cabin might be enveloped in a misty fog and loose articles like paper and small items might fly around the cabin. Passengers would presumably be wearing their seat belts and therefore be in little danger of being sucked into the sky.
Of course, we may never know what actually happened during the many hours Flight 370 was aloft. Whether it was because of lack of cabin pressure or some other reason, all communication ceased after the copilot, Fariq Abdul Hamid, apparently did the final sign off, saying, “all right, good night.”