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.

Lyon told lawmakers that in 2005 USAF rejected a back-up oxygen system that would have cost the government about $500,000 to ensure that the additional 15.4 lb. did not weigh down the aircraft. The weight issue is no longer a concern. “The performance of the aircraft is so magnificent that 15 lb. is not going to hurt,” Lyon says.

The general says he is looking at “intersections” among the findings of the Air Force's Science Advisory Board (SAB) and the NASA report that will be folded in with the final document he provides to Panetta. “Our work is not done,” he says.

The oxygen concentration issue is still being addressed by the Air Force. For now, the service is expected to follow through on the recommendations of an SAB report that calls for replacing the upper-pressure garment, seeking a back-up oxygen system and another system to avoid ground collisions—in case of pilot blackouts. Lyon expects to retrofit the upper-pressure gear with new valves by year-end at a cost of $3.7 million. The backup oxygen system will begin to enter the fleet in January at a fleet-wide cost of $51 million. A $26 million ground-collision avoidance system will also be added.

Lawmakers' reactions to the testimony are decidedly mixed. Rep. Roscoe Bartlett (R-Md.) says he hoped the hearing would ease the minds of pilots and their families. But Rep. Jackie Speier (D-Calif.) is not sanguine that the underlying cause has been found. “I'm just not convinced we have the answer,” she says. “I think NASA needs to be privy to all the information. And all the reports should be made public.”

Rep. John Runyun (R-N.J.) emphasizes that pilot safety must be paramount. “We understand that we can change the physiology of a machine, but we can't change the physiology of a human being,” he notes. “We have to be really cautious.”

F-22 Life-Support Investigation Benchmarks
November 2010:
Capt. Jeff Haney dies after F-22 crash during routine training mission in Alaska.
May 2011:
F-22 fleet ordered to stand down.
June 2011:
Air Force Scientific Advisory Board (SAB) begins study of F-22 incidents.
September 2011:
F-22 resumes flights.
September 2011-March 2012:
Pilots report 11 additional incidents.
January 2012:
SAB delivers report to the secretary and chief of staff. Air Combat Command (ACC) establishes a Life Support System Task Force, which continues to examine both the issues of supply and quality of oxygen in the F-22.
April 2012:
NASA accepts request to investigate ACC’s ongoing root-cause analysis; and the F-22 life-support system.
May 2012:
Defense Secretary Leon Panetta restricts F-22 flights to below 44,000 ft. to allow for retrofit of valve in upper-pressure garment.
August 2012:
NASA Engineering and Safety Center delivers independent report to Air Force warning against a “normalization of deviance” in accepting F-22 health problems.
November 2012:
Air Force to begin fielding upper-pressure garment with new valve.
January 2013:
First aircraft to receive backup oxygen system.
Sources: Scientific Advisory Board report; House Armed Services Committee hearing testimony; and Maj. Gen. Charles Lyon, director of operations at Air Combat Command