Two lawmakers on Tuesday demanded an explanation from the Air Force for why two more pilots have reportedly experienced oxygen problems in the F-22 Raptor, the world's most expensive fighter jet.
''This seems to be a never-ending saga," Sen. Mark Warner, D-Va., told reporters in a joint conference call with Rep. Adam Kinzinger, R-Ill.
The lawmakers were reacting to two recent episodes, the latest in a series over the past 18 months calling the plane's safety into question.
On July 6 at Joint Base Pearl Harbor-Hickam in Hawaii, an F-22 pilot declared an in-flight emergency because he was experiencing symptoms of hypoxia, or oxygen deprivation.
On June 26 at Joint Base Langley-Eustis in Virginia, another F-22 pilot pulled his emergency oxygen handle during landing because of what the Air Force characterized as "discomfort" from intermittent air flow into his mask during flight.
In addition, Warner and Kinzinger said they were concerned about what happened May 31 at Tyndall Air Force Base in Florida, where a pilot hit the runway without his landing gear down. They said that it was premature to assume that hypoxia was the cause but that the episode should be investigated.
''I have concerns about the Air Force's ability to get to the bottom of this," Warner said, adding that, "my patience is running thin."
In a letter Tuesday to Michael B. Donley, the Air Force secretary, Warner and Kinzinger asked for a full accounting of all the occurrences of hypoxia-like symptoms in Raptor pilots since the plane went into service in 2005. So far the Air Force has said there have been 36 episodes, with 21 of those unexplained — overall a far greater number per flight hour than in other types of aircraft in its fleet. (The two most recent occurrences and the episode at Tyndall are not included in the 36.)
Air Force officials have been struggling to understand for more than a year why some pilots become dizzy or disoriented during F-22 flights or immediately afterward. Last month they appeared to have made a breakthrough: Investigators said they believed that a pressure vest was restricting pilots' breathing and that narrow oxygen hoses were leaking or not delivering enough air. The Air Force ordered pilots to fly without the vest.
But the two pilots who experienced the recent hypoxia symptoms at Langley and Hickam were not wearing vests.
Lt. Col. Pat Ryder, an Air Force spokesman, said Tuesday that after the Air Force reviews the letter from Warner and Kinzinger, "an appropriate and timely response will be provided."