What happened
On the fifty-third test flight of the aircraft, the crew departed from runway 10 at Wisley Aerodrome at 10:17 GMT. The mission objective was to perform stall testing across various configurations while maintaining a center of gravity at 0.38 SMC. After departing under visual meteorological conditions, the aircraft climbed to 17,000 feet on a westerly heading.
By 10:26, the co-pilot notified tower that stall tests were beginning at flight level 170. The crew successfully completed four stalls with the landing gear and flaps retracted. Following a final radio contact at 10:36, the crew lowered the flaps to evaluate stalling characteristics in that specific configuration. Approximately two minutes later, while between 15,000 and 16,000 feet, the aircraft entered a stall.
During the recovery attempt, the elevators initially reacted to pilot input but then drifted to a fully up position despite significant physical force applied to the control column. The aircraft began a rapid descent at approximately 180 ft/sec in a largely horizontal attitude. During this fall, the aircraft experienced two right banks and one left bank. Although the engines were briefly advanced to full power—causing a sharp nose-up pitch followed by a nose-down pitch when power was reduced—the aircraft remained in a stable stall.
Witnesses observed the aircraft approaching from the southwest at a low altitude, noting a sharp sound in the air and unusually low engine noise. The aircraft impacted the ground at approximately 10:40 in a flat attitude, sliding briefly before an explosion and fire occurred. The accident resulted in seven fatalities, involving four engineers and three test pilots.
Findings
Investigation into the flight recorders and radio communications revealed that during the fifth stall, the angle of incidence reached a critical point where the elevator could no longer provide enough effectiveness to facilitate recovery. The primary cause was determined to be an insufficient nose-down pitching moment caused by the elevators becoming ineffective just beyond the stall, preventing the crew from counteracting the increase in incidence.