Page 27 - Dec18T

A Medical Look at Hypoxia
Is it actually safe to operate pressurized aircraft at cabin altitudes above 10,000 feet?
by Kevin Ware
Over the years, there have been numerous NTSB reports of pilots flying pressurized twin and turbine aircraft in the mid to high 20 flight levels, failing to respond to radar controllers and ultimately crashing. One of particular note occurred several years ago
when a pilot of a pressurized piston twin took off from New Orleans and headed on an IFR flight plan across the Gulf of Mexico toward the central Florida coast. About an hour into the flight, when well off-shore, he stopped responding to calls from the controllers, causing them to scramble two Air Force jets to intercept the aircraft and see what was going on. The military pilots then reported seeing an elderly male pilot slumped over the control wheel and apparently unconscious. They fol- lowed the airplane as it began a gradual descent of wide circles until it crashed into the ocean and disappeared in 10,000 feet of water. The aircraft and its pilot were never seen again.
The NTSB blamed the crash on an aircraft pressurization failure, which lacking any evidence to the contrary was not an unreasonable thing to do. But when all factors are considered, the risk of that pilot having an incapacitating physiologic event at altitude may have actually been a much better explanation. Which begs the question, just how safe is it for pilots (especially of a certain age) to be flying these aircraft in the flight levels at or near their maximum operating altitude with cabin altitudes of 10,000–12,000 feet?
The truth of the matter is, sudden depressurization events in general aviation aircraft are not common. The reason for this is that the pressure differential is quite low, and the basic structure is well designed for that purpose. Plus, most airframes simply do not have that much time or “cycles” on them. Slow depressurization events following maintenance are more common as they result from work done that compromises the cabin’s sealed structure. But these are generally carefully checked for on post maintenance flights and fairly obvious to the pilot. Particularly if the aircraft is piston-
December 2018
TWIN & TURBINE • 25
PHOTO COURTESY OF PAUL BOWEN PHOTOGRAPHY