NTSB report says excessive input at rotation during test flight caused business jet to stall, killing all three on board
The crew of a Bombardier Challenger 604 that crashed on a test flight on 10 October 2000 lost control of the aircraft and hit the ground within 12s of take-off, according to a US National Transportation Safety Board (NTSB) report. The aircraft stalled too low for recovery to controlled flight, probably due to the excessively vigorous input of elevator at rotation.
The aircraft was intentionally ballasted with the centre of gravity (CG) near its aft limit so the effectiveness of a modified pitch-feel simulator (PFS) could be tested. During the 21s roll to rotation speed at Wichita airport, Kansas, the aircraft's fuel began migrating aft, particularly in its in-line fuselage auxiliary tanks, which are not isolated from each other. This effect was exaggerated by a rapid rotation rate of 9.6¡/s to a nose-up pitch of 20¡, more than three times the recommended rotation rate.
An NTSB investigation of the aircraft commander's recent flights discovered that although he had a recent history of commanding excessively rapid rotation rates he had not been corrected for doing so. The aircraft lifted off at 143kt (265km/h) and within 3s the sound of the stickshaker stall warning could be detected on the cockpit voice recorder, according to the report. An uncommanded roll to 60¡ right wing down was followed by a roll to wings level, then another roll right to 80¡ bank, wings level again and finally the aircraft hit the ground at a bank angle of 40¡ right.
The stick-pusher had also operated, according to the flight data recorder, but the pilot's response had been to increase the elevator-up input. Both pilots and the flight test engineer died in the accident.
According to the report, when the Challenger went out of control, the CG had moved beyond the aft limit because of fuel migration, but the aircraft would have remained controllable if the pilot had not rotated so fast. An additional contributory cause of the accident, the NTSB says, is the fact that Bombardier did not have a well-managed risk-management system for the Challenger programme in place, although one was already under development.
Source: Flight International