(WASHINGTON) -- There is no single malfunction to blame for the mystery oxygen problems with America's most expensive fighter jet, the F-22 Raptor, but the Air Force believes it has solved the potentially deadly riddle anyway by identifying a few contributing factors, a top Air Force official said Tuesday.
"In the end, there is no smoking gun," Maj. Gen. Charles Lyon, head of an Air Force F-22 investigation board, told reporters. "We have assembled the pieces of the mosaic... I have high confidence that we have eliminated the major contributors to this problem."
The "mosaic" of issues, Lyon said, includes a malfunctioning valve on the pilot's upper pressure vest, the size and shape of hoses and connectors in the pilot's gear and, for a period, a charcoal filter that the Air Force installed after the problems began to try and catch potential contaminates.
Lyon's comments elaborated on an announcement by Pentagon spokesperson George Little earlier this week that the military was "confident" the F-22 problem was solved and that there was a plan to lift strict flight restrictions on the $420 million-a-pop planes.
The $79 billion Raptor fleet was the subject of an ABC News Nightline investigation in May, which found that in more than two dozen cases since 2008, F-22 pilots had experienced unexplained incidents of what the Air Force called "hypoxia-like symptoms" in mid-air. Hypoxia is defined as a lack of oxygen to the brain and is characterized by dizziness, confusion, sluggishness and poor judgment.
In one case last year, a pilot became so disoriented that his plane dropped down and skimmed treetops before the airman managed to pull up and save himself. Days later, the Air Force grounded the entire fleet while they investigated the mystery problem.
After nearly five months of searching, and with no solution found, the Air Force cautiously allowed the planes back in the air. Only days after that, the Air Force awarded the plane's manufacturer, Lockheed Martin, a nearly $35 million contract in part to help identify the source of the problem, but they too came up empty handed.
Lyon said on Tuesday that he believes a "vast majority" of the incidents were caused by one or a combination of the contributing factors he listed.
He also said that the faulty parts were totally unrelated to a fatal F-22 crash in Alaska in November 2010 in which Capt. Jeff Haney's plane suffered a malfunction that shut off his oxygen completely.
Lyon was unable to explain why on six other occasions, ground crews had reported experiencing hypoxia-like symptoms while working on the jets, but said they could have been feeling off due to anything from dehydration, poor diet or breathing in nearby jet exhaust.
F-22 pilots have already been ordered to ditch the pressure vests and the Air Force will soon begin testing a new valve on the pressure vest. The service is also in the process of installing an automatic emergency back-up oxygen system to the planes but does not expect to be finished until next spring.
Despite costing an estimated $79 billion, no jet in the entire F-22 fleet -- some 185 planes -- has ever seen combat. From Iraq to Afghanistan to the no-fly zone over Libya, the Air Force said the planes simply weren't necessary.
Over the weekend, the Air Force deployed a squadron of F-22s to Kadena Air Base in Japan. All of the planes reached their destination without incident, Lyon said.
Copyright 2012 ABC News Radio