WASHINGTON -- The crash of the only flying prototype of the Air Force's future air superiority fighter last April was not caused by any fundamental design flaw in the F-22 aircraft, the service said Thursday.
'The aircraft and flight control system operated as designed,' said an Air Force accident investigation report. 'There was no indication of any system failure or malfunction.'
Nor was the crash the result of pilot error, as some experts earlier theorized, the report said in effect.
Rather, it said, the mishap resulted from a slight mismatch between the instructions in the aircraft's flight manual, which Lockheed test pilot Tom Morganfled was following, and those which the test flight engineers had specified for the particular test being flow the day of the crash.
Those instructons related to use of the F-22's thrust vectors, which enable the pilot to direct the blast from the aircraft's jet engines and make the plane more maneuverable in aerial combat.
The F-22's instruction manual permits the pilot to land the plane with with his thrust vectors activated provided he takes certain precautions, all of which Morganfeld had done.
The flight test program or 'test card' had called for the pilot to turn his thrust vectors off during both takeoff and landing, although it described this as an added precaution rather than as a requirement.
Morganfeld saw no need to take that extra precaution, the report of investigation report said, because he thought it was unnecessary.
'The pilot did not follow the flight test card procedure,' it said, 'because...the thrust vectoring system worked properly throughout testing, no restriction prohibited thrust vectoring, and he thought the flight test engineers agreed (that) the practice of turning the thrust vectoring switch off during landings was unnecessary.'
As Morganfeld approached the airfield at Edwards Air Force Base, Calif., for a landing the day of the crash, a videotape showed, his F-22 began bucking like a wild bronco. The test pilot retracted his landing gear and tried to accelerate into a climb.
Instead, the plane slammed down on runway, skidded on its belly for 8,000 feet and burst into flames.
Morganfleld jettisoned the plane's transparent canopy with explosive bolts and jumped from the blazing wreck. He suffered only minor back injuries.
The sole flying F-22 prototype, which burned fiercely for more than a half hour, was a total loss. The Air Force said that the aircraft had completed 90 percent of its test flight program. The F-22 is slated to replace the F-15 as the Air Force's main air superiority fighter after the turn of the century.