The U.S. Air Force's top uniformed officer will be briefed this week on options for lifting a four-month-old grounding of the service's F-22 Raptor air dominance fighter, sources said.
The stealthy twin-engine fighters were idled May 3 after pilots suffered 14 "hypoxia-like" incidents and toxins were discovered in some pilots' bloodstreams. Sources said Air Force officials are still working to identify the problem with the jet's oxygen systems but believe the risks have been reduced enough to lift the grounding and officials are discussing what limitations to impose on the aircraft while the investigation continues.
At a Sept. 2 meeting between the lead investigator and Gen. Norton Schwartz, Air Force chief of staff, some officials discussed limiting the F-22 to a 40,000-foot operating ceiling, while some in the service's physiology community pushed for even lower altitudes. The operational F-22 community is pushing for the restoration of the jet's full 60,000-foot flight envelope.
"The meeting had a lot of discussion of even a lower altitude restriction than 40,000 feet and a lot of things that don't make sense physiologically in terms of operations," one source said.
Lt. Col. Sam Highley, a spokesman for Schwartz, said in a Sept. 6 email that the meeting was not meant to be a final report, but an update from the Air Force's Scientific Advisory Board (SAB).
"On Friday, Sept. 2, 2011, General (ret.) Gregory S. Martin provided General Schwartz an update on the progress of the Scientific Advisory Board's study on all of the service's aircraft equipped with oxygen generation systems," Highley wrote. "This was not a final report, but an in-progress update. The SAB continues the study and expects to deliver a final report later in the Fall."
The Air Force will not return the Raptor to flight before it was safe to do so, Highley said.
"While the Air Force continues to work diligently toward an expedient return to flight operations, the stand-down of the F-22 fleet will continue until senior leadership can ensure we mitigate risks to a level that's appropriate for the urgency of the mission," he said.
The operational F-22 community is dissatisfied with the Air Force's cadre of physiologists and has been clamoring for one of its own to be included on the team. Sources said the man they want to help with the investigation is a former Air Force flight test engineer and rated physiologist - a pilot who is later trained as physiologist - Kevin Divers, who runs an aerospace physiology consulting practice called Warrior Edge. Divers was a member of the F-22 Combined Test Force during the jet's developmental testing and operational testing.
During his time in the Air Force, Divers said he saw a disturbing trend.
"The trend that I saw, as rated-physiologists left the career field, is that the aerospace physiology officer leans more on academic knowledge," he said.
Physiologists don't fully comprehend the safety systems built into the modern aircraft, Divers said, but moreover, most don't have the real-world experience in an aircraft. The consequence is that it has made it harder for the Air Force to get to the bottom of the problem.
"There is a major gap between research and operational knowledge of the F-22 that could be causing this delay," he said.
The lack of experience has also created "an aircrew perception that the career field doesn't understand its customer any more," Divers said.
A rated physiologist by contrast knows the aircraft and its systems from an operational point of view.
"I know all of their flight equipment - the [onboard oxygen generating system] OBOGS, the entire plumbing of the aircraft to the OBOGS - because I had to study it and look at it from the safety standpoint for the pilots," Divers said. "My pilot training experience taught me to break down subsystems and know the aircraft to the level that the aircrew has to know it. Air Force physiologists aren't trained that way coming into the Air Force."
The Air Force wouldn't directly address Divers' concerns.
"The SAB study is ongoing and the Air Force continues to deliberately study all aspects of F-22 flight safety," said Air Force spokesman Chad Steffey. "This particular investigation involves a strong fact-finding analysis with deliberation among a cross-section of highly qualified scientific experts."
Another aerospace safety expert said it is always helpful to have a pilot who is rated as a physiologist working on such a problem. Such a pilot would be intimately familiar with the aircraft's systems and the effects on the human body, said Hans Weber, who owns Tecop International, a San Diego-based aerospace consulting firm and a former member of the Federal Aviation Administration's Research, Engineering and Development Advisory Committee.
Weber said he was dismayed that the Air Force, after four months, had still not pinpointed the exact cause of the Raptor's oxygen system problems.