test flight on March 25 at Edwards Air Force Base, Calif., almost lost consciousness during a high-g maneuver and failed to pull the aircraft out of a steep, high-speed dive in time to recover.

Lockheed Martin test pilot David Cooley was killed immediately by windblast forces when he ejected from the F-22 at 765 knots equivalent airspeed, roughly 150 knots above the Aces II ejection seat’s design limits, U.S. Air Force accident investigators say.

The mishap occurred on the third of three high-speed, high-g test runs to evaluate how opening the side weapons bay affects aircraft performance. The tests involved rolling inverted at Mach 1.6 and 25,000 feet, performing half of a split-S maneuver, then rolling upright and pulling out of the dive.

Investigators believe that because of inadequate anti-g straining the pilot suffered “almost” g-induced loss of consciousness (A-LOC) and lost situational awareness, allowing the aircraft to enter a steep, high-speed dive from which recovery was not possible. Anti-g straining squeezes the heart and keeps blood flowing to the head. The pilot’s technique was evaluated as ineffective based on an audio recording. While he did not lose consciousness, his attention became focused on fighting off the symptoms of A-LOC.

Relatively incapacitated, the pilot did not begin the recovery immediately on completing the third test. The F-22 rapidly lost altitude as the dive angle steepened. At 14,800 feet, 83 degree nose-low and Mach 1.49, the pilot rolled the aircraft upright, but it was too late.

Investigators say the escape system functioned as designed, but the ejection speed was beyond anything seen even in sled testing. The ACES II seat is designed for a maximum 600 knot ejection speed, but there is an 80 percent chance of major or fatal injury above 550 knots.