Some F-22 Fighter Pilots Wary of Troubled $79 Billion Jets Some pilots picked to jump into the cockpit of America's most advanced and expensive fighter jets are declining the normally coveted post because of a mysterious oxygen system problem that the Air Force has not been able to solve despite years of investigation, according to a top Air Force official. A "very small" number of the 200-something stealth F-22 Raptor pilots have requested to either not fly the next-generation fighters or to be reassigned altogether, Air Force Gen. Mike Hostage told reporters Monday. "Obviously it's a very sensitive thing because we are trying to ensure to that the community fully understands all that we're doing to try to get to a solution," said Hostage, commander of the Air Combat Command, which oversees F-22 operations. The F-22 Raptor, America's most expensive fighter, is the subject of an upcoming ABC News investigation. Tune in Wednesday to ABC News' "World News With Diane Sawyer" at 6:30 p.m. ET and then "Nightline" at 11:35 p.m. For years the F-22 has been plagued with an extremely rare, but potentially deadly problem in which its pilots experience what the Air Force describes as "hypoxia-like symptoms" in mid-air. Hypoxia is caused by a lack of oxygen to the brain and can be characterized by dizziness, confusion, poor judgment and, eventually, loss of consciousness. During one such incident, a pilot apparently became so disoriented that his plane dropped down and skimmed treetops before the pilot was able to recover and head back to base, an Air Force spokesperson told ABC News. In a separate case -- and one that the Air Force maintains is unrelated to the current problem -- F-22 instructor pilot Capt. Jeff Haney died in a crash in Alaska in 2010 after a critical malfunction cut off his oxygen completely in mid-air. The Air Force also does not know what originally caused that malfunction. Later, in 2011 the Air Force grounded the entire fleet of F-22s -- more than 180 planes made by defense contracting giant Lockheed Martin for an estimated $79 billion -- for nearly five months as they investigated the source of the oxygen problems. But the Air Force could not find a single "smoking gun" and cautiously allowed the planes to go back in the air. In the meantime, Lockheed Martin was awarded a nearly $25 million defense contract for various F-22 related projects, including helping find the cause of the oxygen issue. But the problem persists. The Air Force told ABC News that in the time since the planes went back into the air in September 2011, there have been at least eight other instances of pilots experiencing the hypoxia-like symptoms. Several Air Force officials have said they are doing everything they can to ensure the pilots' safety as the F-22 continues training and homeland security missions. Despite going combat operational in late 2005, none of the $143 million-a-pop planes have been used in combat. Recently an unknown number of the jets were deployed to a base in the United Arab Emirates, just a short hop over the Persian Gulf from Iran.