A culprit is now confirmed for the respiratory curse affecting an alarming number of US Air Force pilots flying the Lockheed Martin F-22, and it is not what anyone suspected.
At least part of the problem is now blamed on the partial pressure suit that, ironically, is designed to help pilots cope with the effects of high-g manoeuvres, which entail oxygen loss.
The F-22 is designed to fight and manoeuvre at altitudes up to 60,000ft, a flight envelope that strains the limits of physiological science. Other aircraft have flown higher and faster, but none has had the acrobatic agility of the F-22 in such thin air.
That kind of performance is apparently too much for the USAF's bespoke Combat Edge pressure suit to handle. Rather than protecting the pilot's chest, the suit at such extreme altitudes in aggressive manoeuvres constricts too tightly when inflated, sometimes collapsing tiny air sacs in the pilot's lungs. The pilot, however, lands but remains oblivious to the damage. Damaged air sacs need time to rebuild. F-22 pilots at two bases, in particular - namely Elmendorf and Langley - often fly more than once a day. On subsequent flights, the pilots' constricted lungs lack capacity to absorb enough of the filtered, 93% oxygen flowing into their masks.
The combined result of these phenomena partly explains the epidemic of hypoxia-like symptoms reported by F-22 pilots over the last three years - and almost exclusively by pilots at Elmendorf and Langley. It does not explain why maintenance workers on the ground have also reported lung problems.
Bad pressure suits are not the F-22 pilot's only oxygen problem. The F-22 lacks an automatic back-up oxygen system, requiring the pilot to activate an awkwardly placed pull-up ring in the event of primary system failure, while unable to breathe. Automating the back-up oxygen supply would probably have saved the life of Capt Jeff Haney, who died in a November
Secretary of Defense Leon Panetta has rightly ordered the USAF to install an automated back-up system on the F-22, but it will not be cheap. Likewise, the F-22 pilot community will also need to qualify a partial pressure suit tailored to the unique physiological circumstances encountered only by that stealth fighter.
Neither change may seem affordable in the current budget climate, but it is a bill that simply must be paid. The F-22 is an exquisite aerodynamic specimen that tolerates no shortcuts for life-support equipment.
(This first appeared as the lead Comment article in 12 June 2012 Flight International)