Wednesday, December 14, 2011

USAF Board Blames Pilot, Not Oxygen System, in F-22 Crash

A U.S. Air Force Accident Investigation Board (AIB) report is blaming the Nov. 16, 2010, crash of an F-22 Raptor on Capt. Jeff "Bong" Haney - despite a malfunction of the jet's bleed air intakes, which caused an automatic shutdown of multiple aircraft systems including the primary oxygen system.
An aircraft's engine bleed air system extracts air from a jet engine's compressor section to generate power and supply gases for an aircraft's life support system, among other systems.
The AIB report confirms Defense News' Sept. 8 report, in which an industry source and a pilot both said that a bleed air malfunction had caused the crash by shutting down the oxygen system. The AIB, however, places the blame on Haney for not reacting quickly enough to activate the jet's emergency oxygen system or recover from a dive he inadvertently entered into as he struggled to regain his air supply.
"I find the cause of the mishap was the MP's [mishap pilot] failure to recognize and initiate a timely dive recovery due to channelized attention, breakdown of visual scan and unrecognized spatial disorientation," wrote Brig. Gen. James Browne, president of the AIB.
The F-22's On-board Oxygen Generating System (OBOGS), which supplies breathing air to the pilot and has been under investigation for most of the year, did not malfunction and wasn't a contributing factor, the report said. But the crucial device did shut down because of the bleed-air problem. In September, Air Force Chief of Staff Gen. Norton Schwartz said oxygen had not played any role in the crash.
The report notes that "the MP most likely experienced a sense similar to suffocation," but also rules out hypoxia as contribution factor however despite the shut down of the oxygen system.
"Due to the high affinity of oxygen to hemoglobin, the MP would have had adequate blood oxygen supply after the OBOGS failed," the AIB report states. "It was concluded that the late recognition of the MA's [mishap aircraft's] unusual attitude and appropriate corrective actions attempted by the MP demonstrates that hypoxia was not a factor in this mishap."
A knowledgeable source agreed that Haney would not have fully succumbed to hypoxia, but would have been showing symptoms. Despite what the report says, the source said hypoxia would have played a role even if the pilot had not been rendered unconscious.
"The rate at which he descended, though, he would have been at a hypoxia-safe altitude within time to have not fully succumbed to hypoxia and should have only had symptoms versus unconsciousness," the source said.
The environmental control system (ECS), air cycle system, On-Board Inert Gas Generating System (OBIGGS), cabin pressure and OBOGS were all shut down when the aircraft's computer shut off the malfunctioning bleed-air system, according to the AIB report. The bleed-air system remains closed in the event of a malfunction to prevent fires.
The aircraft's memory unit showed "partial pressure to the MP's [mishap pilot] oxygen stopped shortly after 19:42:37 L, which would lead to severely restricted breathing," the accident report reads.
However, Haney did retain enough consciousness to attempt a recovery from a steep dive the aircraft entered into right before the crash. It was too late, however, as the Raptor impacted the ground a scant three seconds later.
However, Haney did not manage to active the Emergency Oxygen System (EOS) to supply him with air, which he needed to do in case the OBOGS shutdown. As the report notes "severely restricted breathing is a physiological symptom which would have prompted the [mishap pilot] to active the EOS."
Pilots have said that the emergency oxygen supply is notoriously difficult to use in the Raptor.
The AIB report states that as Haney struggled for air, "he channelized his attention on restoring airflow to his oxygen mask."
As Haney fought to restore his oxygen supply, he inadvertently began to roll the aircraft and his "visual scan" of the aircraft's instruments and external situation broke down. He entered into a state of "unrecognized spatial disorientation," according to the AIB report. The aircraft rolled 240 degrees and dropped to a 53 degree nose down attitude. Had Haney not been distracted by trying to breathe, he would have recognized the problem, the report reads. Haney didn't make any intentional control inputs for some 39 seconds.
"The fact that the [mishap pilot] went from a controlled flight regime to an unusual attitude and did not take corrective actions for 30 seconds suggests he had unrecognized spatial disorientation," the AIB report reads. "At 19:42:24L the [mishap pilot] recognized the [mishap aircraft's] position and attempted to perform a dive recovery."
Ultimately, the Air Force chose to blame Haney rather than attribute the crash to a malfunctioning bleed-air system and a difficult to use emergency oxygen supply.

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