The U.S. Air Force approved a resumption of flight operations by the Lockheed Martin F-22 Raptor, ending a four-month standdown ordered after pilots experienced symptoms of hypoxia. The suspected source of the problem, the aircraft’s onboard oxygen generation system (Obogs), remains under study.
Each of the 170 F-22s will undergo inspection of the aircraft’s life support systems before returning to flight, with follow-on daily inspections, the Air Force said. Before the standdown May 3, the fleet was already restricted to flying below 25,000 feet. Aircraft are now authorized to fly above 50,000 feet. Pilots will use additional protective equipment and undergo baseline physiological tests, the service said.
“We now have enough insight from recent studies and investigations that a return to flight is prudent and appropriate,” stated Gen. Norton Schwartz, Air Force chief of staff. “We’re managing the risks with our aircrews, and we’re continuing to study the F-22’s oxygen systems and collect data to improve its performance.” The service said it will release a report later this year based on concurrent studies of a safety investigation board and the Air Force Scientific Advisory Board.
The safety standdown followed 12 separate reported incidents over a three-year period beginning in April 2008 in which pilots experienced hypoxia-like symptoms, the Air Force said. The altitude restriction was imposed in January, following the Nov. 16, 2010, fatal crash of an F-22 in Alaska.
The F-22 uses an Obogs supplied by Honeywell. Media reports of similar oxygen deprivation problems involving Navy F/A-18C/Ds fitted with a Cobham system prompted Cobham to issue a statement on September 12. The company said two hypoxia-related F/A-18 fatal accidents between 2002 and 2009 “were not caused by Cobham’s Obogs concentrators, regulators or components.” The company said one of the accidents involved an aircraft equipped with a liquid oxygen system, not an Obogs. The other involved an Obogs-equipped aircraft, “but the root cause of that accident was not” Cobham’s equipment. F/A-18 hypoxia incidents between 2001 and 2004 “were traced to leaking aircraft plumbing [hoses and tubes] outside the scope of Cobham’s Obogs content.”
Cobham says it enjoys 85 percent of the world market for Obogs, supplying equipment on 30 aircraft models and 3,000 operating aircraft. The technology has accumulated 6.6 million flight hours. Cobham-equipped F-15Es and F-16s stationed at the same bases as the F-22 have experienced no Obogs hypoxia incidents, the company added.