Why have F-22 pilots passed out at the controls? Air Force says it has answer.

Anna MulrineThe Christian Science Monitor

Why have US military pilots been passing out at the controls of their F-22 fighter jets?

That has been the mystery vexing Pentagon officials for more than a year. On Tuesday, they announced the results of a wide-ranging investigation into dangerous malfunctions surrounding the most expensive fighter jet in military history.

“What gave the Air Force grave concern last year was the unexplained nature of the incidents and the incident rates,” says Maj. Gen. Charles Lyon, director of operations for Air Combat Command, who headed the investigation. “At one point we got up to 11 incidents, which we could not explain.”

This was a grave concern for pilots as well. In May, two F-22 pilots went public on CBS saying they refused to fly the plane after becoming woozy and dizzy in mid-flight.

The problem is largely due to a pressurized vest that pilots wear when they fly, as Defense Secretary Leon Panetta said at a press conference last week. It has inflated “before it should” in some cases, creating tightness in the pilots' chest. This has been caused by a faulty valve, installed to protect against chemical attacks.

In turn, pilots experienced hypoxia, or oxygen deprivation. “It’s like putting a corset around your chest,” Lyon added in a Pentagon briefing Tuesday. “You’re going to find it harder to breathe.”

The consequence: “lightheadedness, tingliness, and numbness.”

Air Force officials decided to ground the F-22 in May 2011, after nearly a dozen cases of hypoxia were reported including the fatal flight of Joint Base Elemendorf-Richardson pilot Jeffrey Haney, who crashed near Cantwell, Alaska in November of 2010.

A subsequent Air Force investigation said that there was a malfunction with the oxygen supply in the jet piloted by Capt. Haney, but also that while Haney was focusing his attention for 50 seconds on re-establishing the flow to his oxygen mask, he inadvertently moved the aircraft, resulting in "spatial disorientation" that led to an unrecoverable dive. Procedure called for the activation of the Emergency Oxygen System or for Haney to lower his mask from his face. The investigation found that he did neither.

Haney’s sister, Jennifer Haney, strongly disagreed with the Air Force assessment.

"I'd like to think it's easier to blame Jeff. He's not here to defend himself,"  she told ABC News in an exclusive interview. "To them, Jeff was a number, it feels like sometimes. But those jets are worth a lot of money.”

The Air Force resumed flights in September, and since then, nearly a dozen more possible such cases have been reported, according to Pentagon officials. US military officials said they could not estimate the cost of fixing the valve and vest, although they said it would certainly be in the “millions” of dollars.

The F-22 is a controversial symbol of American air power. Developed with enemies like the Soviets in mind, F-22s have yet to fly a single combat mission. Yet their technology is cutting edge, potentially allowing the United States to launch stealth attacks by flying at supersonic speeds and taking out enemy aircraft using advanced radars.

“The F-22 is the highest icon of the Air Force: It’s the embodiment of their vision of warfare and technology,” says Winslow Wheeler, director of the Straus Military Reform Project within the Project on Government Oversight.

The result, he says, is that Air Force officials "regard maintaining the image of the airplane as more important than maintaining the health of the pilots.” He adds, “It’s an unkind and simple assessment, but it’s true.”

Gen. Mike Hostage, head of Air Combat Command in Virginia, told reporters April 30 that the fighter jet is safe to fly. “Right now, we believe that risk – although it’s not as low as we would like it – is low enough to safely operate the airplane at the current tempo,” he said.

The last reported, unexplained incident took place March 8, Lyon said. F-22 pilots have since logged some 10,000 flight hours without an incident.