US Air Force chief of staff Gen Norton Schwartz says an accident investigation board did not blame Capt Jeffrey Haney for the fatal Lockheed Martin F-22 Raptor crash on 16 November 2010.

"We did not assign blame to the pilot," Schwartz told the US Congress on 6 March. He acknowledged that the aircraft's bleed air valves - from which the jet's oxygen is derived - had shut down, depriving Haney of oxygen, and that this was a contributing factor.

However, Congressman Jim Moran countered: "The accident board blamed him."

Accident board president Brig Gen James Browne stated in the report: "I find the cause of the mishap was the [mishap pilot's] failure to recognise and initiate a timely dive recovery due to channelised attention, breakdown of visual scan and unrecognised spatial disorientation."

The sequence that led to Haney's crash began when his F-22 experienced a still-unexplained oxygen leak in the engine bay. As a precaution, a fire suppression system automatically closed the bleed air valves that feed compressed air to the onboard oxygen generation system.

As a result, Haney was forced to activate the emergency oxygen supply. However, he struggled to reach the pull-up ring while unable to breathe. At the same time, he may have inadvertently put the aircraft into a steep dive.

The onboard data recorder showed that Haney attempted a violent pull-up manoeuvre less than 3s before impact, but it was already too late and the F-22 crashed into a remote Alaska valley.

F-22 crash site - USAF 

© US Air Force

The accident investigation board's determination that Haney was at fault has been widely maligned within the USAF pilot community, and is being investigated by the Pentagon's inspector general. The latter's move is highly unusual, one source familiar with such investigations says.

The air force, meanwhile, has been unable to find a single root cause for a series of airborne incidents where pilots have suffered from symptoms resembling hypoxia, Schwartz says.

The USAF has taken precautionary measures such as adding new sensors and air filtration systems, and having the pilots wear pulse-oximeters.

The F-22 Raptor fleet has flown a combined 8,000h since last year's five-month grounding of the stealth jet, but Schwartz acknowledges that there have been several incidents since the flight ban was lifted.

Source: Flight International