DoD Tester: Toxins Suspected in 2011 Raptor Grounding

A Jan. 13 report from the Pentagon's top tester said the U.S. Air Force grounded its F-22 Raptors last year "due to suspected contamination problems associated with the aircraft environmental control system and associated onboard oxygen generation system form later April through late September 2011."

A U.S. AIR Force F-22 Raptor prepares to land at Joint Base Elmendorf-Richardson, Alaska, on Nov. 16, two months after the service lifted its fleetwide grounding. (Staff Sgt. Sheila deVera / U.S. Air Force)

Complied by the Pentagon's chief operational tester J. Michael Gilmore, the review confirms Defense News' July 25, 2011, report that toxins entering the cockpit of the Raptor had caused more than a dozen incidents that resembled hypoxia.

Since the grounding was lifted in September, the Raptor has flown more than 6,000 times. More incidents have occurred, despite Air Force precautions that include installing charcoal-based filters and having pilots wear pulse-oximeters to alert them of problems.

"There have been approximately 90 events of interest and 15 are being investigated for potential physiological incidents -- 8 involving pilots and 7 involving aircraft maintenance personnel," said Air Force spokeswoman Jennifer Ferrau. "This translates to a 1.8 percent event rate since the return to flight in September."

The Air Force categorizes these occurrences into "events of interest" and "physiological incidents." An event of interest is an aircraft indication, system malfunction or a data point that has not caused symptoms of hypoxia, but is noteworthy for data collection and further analysis, Ferrau said.

"Any event involving hypoxia-like symptoms may be categorized by Air Force Instructions as a physiological incident following an investigation," she said.

A Scientific Advisory Board quick-look study ordered last year by Air Force secretary Michael Donley should be finalizing its report either in late January or early February.

Sources say the service investigators have not found any single explanation for the Raptor's woes. The problem can't be duplicated on the ground, nor do the hypoxia-like incidents occur during any consistent altitude or phase of flight-if in fact the cause happens in the air.