The U.S. Air Force has sent several (exact number unspecified but believed to be four) F-22 fighters to an air base in the UAE (United Arab Emirates). The U.S. said this was not meant to intimidate Iran but Iran quickly announced that it felt intimidated and that it considered the deployment of the F-22s to be an unfriendly act.
Meanwhile, the air force admitted that several of its pilots declared that flying F-22s was intimidating and they would rather not. The air force is handling this one gingerly. There will be no courts martial, and the air force admits that it has not been able to find the cause of air supply failures on the F-22. This is what has some F-22 pilots upset. Despite this the air force continues operating its F-22s. The decision to keep flying was made because the air supply problems have not killed anyone yet and they are rare (once every 10,000 sorties).
The 14 incidents so far were all cases of F-22 pilots apparently experiencing problems. The term "apparently" is appropriate because the pilots did not black out and a thorough check of the air supply system and the aircraft found nothing wrong. There have been nearly 30 of these "dizziness or disorientation" incidents in the last four years, with 14 of them serious enough to be called real incidents. Only one F-22 has been lost to an accident so far and, while that did involve an air supply issue, it was caused by pilot error, not equipment failure. Twice in the past year the entire F-22 fleet was grounded because of the air supply problems. The 180 F-22s comprise the most powerful component of the air force's air combat capability and the brass are eager to find out what is wrong.
The air force has already found some problems with the air supply system (too much nitrogen and other contaminants). The main problem was always about something bad in the air supply. But the air does not go bad in any predictable fashion nor does it become bad enough to cause problems for the pilot. So the air force is still looking for causes.
The U.S. Navy had a similar problem with its F-18s. There were 64 incidents from 2002 to 2009, resulting in two deaths. 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 looked into the navy experience to see if there is anything similar going on with the F-22s. No luck. The air force has looked into a lot of potential causes, without a lot of success.
The air force woes began when it appeared that the F-22 might be having a problem with its OBOG (OnBoard Oxygen Generating) system. The U.S. Air Force also checked the OBOGs in F-16, F-15E, A-10, F-35, B-1, B-2, CV-22, and T-6 aircraft as well. Apparently there were no problems there. The air force believed, at one point, that the F-22 problem might not just involve the OBOG.
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 was also closely studied, to find out how the toxins got in.
OBOGs are standard gear now because aircraft have been staying in the air longer (because of in-flight refueling) and carrying enough compressed oxygen has become untenable. OBOGs were the obvious solution to 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 mineral filter to remove nitrogen from the air taken in to the OBOG and then sending out the oxygen rich air to the aircrew.
