September 24, 2012
Credit: Credit: U.S. Air Force
Jen DiMascio Washington
The F-22 Raptor is renowned for its ability to sustain high-g forces at high altitudes. But keeping the aircraft safe from disaster in those extreme conditions has put a strain on the pilots, and the Air Force continues to struggle to strike the right balance.
The service is taking great pains to show that it has solved the physiological problems that prompted two pilots to tell the television magazine show “60 Minutes” in May that they did not want to fly the aircraft. The new chief of staff of the Air Force, Gen. Mark Welsh, declared during the recent Air Force Association's annual convention: “Don't believe what everyone's [saying] about people not wanting to fly the F-22. There is nobody asking out at the moment, that I know about.” And Air Force Maj. Gen. Charles Lyon, director of operations at Air Combat Command, says the fleet has gone six months without incident and will be able to appeal to Defense Secretary Leon Panetta to resume flights above 44,000 ft. by year-end.
But a Sept. 13 House Armed Services Committee hearing on investigations into the aircraft's troubles highlighted the fact that F-22 program officials waved off a back-up oxygen system in 2005. And NASA rapped the Air Force on the knuckles for dismissing the health concerns of pilots.
The Air Force looked to NASA, twice burned by engineering failures that led to national tragedy, to study the lingering mystery surrounding pilot blackouts and what has become known as “Raptor cough.” While the space agency's Engineering Safety Center found that the Air Force was on the right track, it also took the service to task for the kind of “normalization of deviance” that allowed engineers to overlook flaws on the Challenger before it blew up. “Differences in pilot breathing in the F-22 from other platforms was widely known and accepted as a normal part of flying the advanced aircraft,” principal engineer Clinton Cragg testified. “The acceptance of these phenomena as 'normal' could be seen as a 'normalization of deviance.'”
The assessment found that a high concentration of oxygen at low altitudes can lead to “absorption atelectasis,” in which too much oxygen can wash away necessary nitrogen within the lungs and cause lung tissue to collapse. The effects of high oxygen levels are compounded by the aircraft's “inevitable acceleration,” Cragg said.
“Inappropriate inflation” of the pilots' upper-pressure garment further restricted breathing and reduced overall cardiac output, Cragg testified. “Uncharacterized F-22 life-support system vulnerabilities, such as pressure drops across components in the cockpit,” were also flagged as contributors.
In the long term, NASA recommends end-to-end testing of the life-support system, environmental control system and aircrew flight equipment. The agency also recommends a reassessment of the life-support system in high-performance aircraft and a formal lessons-learned review of the Air Force-led investigation.