July 28, 2011:
The U.S. Air Force is making some progress in finding out what is wrong with their F-22s. It appears that some toxins are somehow getting into the pilot's air supply. This has kept all 168 F-22s grounded for three months, so far. Despite the new findings, the air force still has not nailed down the exact cause of the problem, much less fixed it. The U.S. Navy had a similar problem with its F-18s (there were 64 incidents between 2002-9, resulting in two dead pilots). The navy found that the problem was carbon monoxide getting sucked into the aircraft air system (which the navy modified, eliminating the problem). The air force is looking into the navy experience with these similar problems, to see if there is anything similar going on with the F-22s.
It all began when it appeared that the F-22 fighter might be having a problem with its OBOG (OnBoard Oxygen Generating) system, causing pilots to get drowsy, or even black out, from lack of oxygen. Now it is believed that it was not lack of oxygen, but toxins in the air supply. There were 14 reported incidents of pilots feeling drowsy, or even passing out, because of "bad air." Because of that, on May 3rd, all F-22s were grounded. But the U.S. Air Force is also checking the OBOGs in F-16, F-15E, A-10, F-35, B-1, B-2, CV-22 and T-6 aircraft as well. The problem may just be with the F-22 OBOG, or a general problem with all air force OBOGs. The air force also believed the F-22 problem might not just involve the OBOG, and this seems to be the case. Meanwhile, the grounding is still "indefinite" and will continue until the source of the breathing problem is found, and definitely fixed.
If it goes on too long, the air force may consider fitting some F-22s with the older air supplies, just so some of their newest combat aircraft will be available for combat. In the meantime, pilots and ground crews are using simulators and (for the ground crews) maintenance exercises on the grounded aircraft (in addition to checking a growing list of aircraft components in support of the search for the breathing problem) to retain their skills. But after 210 days on the ground, aircrew will have to undergo extensive retraining to regain combat flying status. This adds a little more urgency to fixing the problem quickly. The grounding also leaves a dozen F-22s stranded at a training base, where they were for live weapons exercises. At least six new F-22s cannot be delivered because of the grounding.
The chief culprit in all this, OBOGs, have been around for over half a century. It's only in the last two decades that OBOGs have become compact, cheap and reliable enough to replace the older compressed gases or LOX (liquid oxygen) as a source of breathable air for high flying aircrew. Each aircraft, especially the F-22 and F-35, gets an OBOG tweaked for space, weight or other conditions specific to that warplane design. It's this custom design that is being closely studied, to find out how the toxins got in.
Because aircraft have been staying in the air longer (because of in-flight refueling), carrying enough compressed oxygen has become untenable, and OBOG solves the problem. Since the 1990s, most American military aircraft have replaced older oxygen systems with OBOG. Most Western nations, and Russia, have followed, at least with their latest model aircraft. Most OBOG systems work by using a chemical reaction to remove nitrogen from the air taken in to the OBOG, and then sending out air with the proper amount of oxygen to the aircrew.
Even helicopter pilots sometimes need additional oxygen. The U.S. Army has encountered this in Afghanistan. That's because helicopter pilots there often operate at high (over 3,200 meters/10,000 feet) enough altitudes that they need oxygen to maintain alertness. Currently, crew members get the oxygen via tubes from 45 kg (hundred pound) tanks. This restricts mobility inside the helicopter. So the army has developed a portable (2.3 kilograms/5 pound) device that you can wear on your chest. A sensor gives you additional oxygen when it detects a need. The PHODS (Portable Helicopter Oxygen Delivery System) provides enough oxygen for 2-3 hours.