Pressure vests were choking F-22 pilots

After years of investigation, the U.S. Air Force has figured out "with high confidence" the "mosaic" of factors that have been almost literally choking the pilots of its premiere fighter jet, the  F-22 Raptor, service officials announced today.

The heart of the problem is an oxygen valve on the early 1990s-vintage pressure vest worn by Raptor pilots. This valve was inflating the vest from the moment the pilots took off, making it hard for them to breathe and leading F-22 pilots to report hypoxia-like symptoms, according to Maj. Gen. Charles Lyon, head of operations for the Air Force’s Air Combat Command.

The pressure vest was originally designed for use by pilots of older fighters, like the F-16 Viper and the F-15 Eagle, and is designed to protect the pilot from the strains associated with pulling extremely high-Gs and emergency de-pressurization at high-altitudes.

"What we also found in our testing that we did this spring and early summer, was that the functioning of that valve was specified to work in an F-15 or an F-16 but it’s not specified to work with an F-22," said Lyon during a July 31 briefing at the Pentagon. "That valve is opening under normal conditions in an F-22, when it should not."

When worn by pilots flying older fighters, the vests normally draw air from their jets’ oxygen systems only when the planes’ pull more than four-Gs, explained Lyon. However, the Raptor’s system constantly pumps oxygen to the pilots from the time they enter the airplane, a feature designed to protect pilots flying through air contaminated by chemical or nuclear warfare, as well as providing more air to them at extremely high altitudes. As a result, "this vest is always inflated on an F-22 pilot, and it should not be inflated until they start to pull Gs. What that does to the pilot is, it restricts his breathing, and it restricts his ability to do normal inhalation and exhalation," Lyon said.

The Air Force is remedying the problem by developing a new high-tension valve that will only allow the vest to inflate when the pilot is pulling high-Gs. The new valve will be distributed throughout the Raptor fleet by the end of 2012 if all goes well in testing, according to Lyon. He declined to say how much the fix  would cost, other than saying it would be in the millions.

What about other incidents where F-22 pilots — and some ground crew — reportedly suffered from hypoxia like symptoms that weren’t traced to the faulty valve and vest combination? Well, since the Air Force exhaustively screened them for toxins and found nothing, it is blaming those incidents on dehydration, under-nourishment, or breathing too much jet exhaust.

The service began investigating the hypoxia-like symptoms after a Raptor crashed in Alaska in November, 2010 while the pilot was reaching to turn on his emergency oxygen system.