The March 3 Bombardier Challenger 300 in-flight upset occurred immediately following the pilots’ response to one of multiple engine indicating and crew alerting system (EICAS) messages, according to the recently published NTSB preliminary report. The report also said the aircraft took off after the EICAS advised of a RUDDER LIMIT FAULT, a message that is normally a no-go item on the Challenger 300 series if the aircraft hasn’t taken off.
Soon after the upset, a passenger told the pilots that another passenger had been injured and the aircraft diverted to Windsor Locks, Connecticut. A waiting ambulance took the passenger to the hospital where she later died.
The twin jet was on an IFR Part 91 flight from Keene, New Hampshire to Leesburg, Virginia. At around 6,000 feet msl while climbing to FL240 and with the autopilot (AP) engaged, the pilots observed multiple EICAS caution messages, including: AP STAB TRIM FAIL, MACH TRIM FAIL, and AP HOLDING NOSE DOWN. Both pilots agreed to use the STAB TRIM FAIL checklist (not the AP STAB TRIM FAIL checklist), which initially called for the stabilizer trim switch to be turned off.
The moment the SIC turned the stabilizer trim switch to off, the AP disconnected, as the crew expected, but then the airplane abruptly pitched up to about 11 degrees reaching a vertical acceleration of about +3.8g.
The airplane subsequently entered a negative vertical acceleration to approximately -2.3g and pitched up again to about 20 degrees and +4.2g. The stick pusher activated during this pitch up and vertical acceleration lowered to about +2.2g. Once the SIC returned the switch to the primary position, the PIC regained control of the airplane and flew manually for the remainder of the flight.
Last June, Challenger 300s were the subject of an airworthiness directive prompted by “multiple in-service events where, following a STAB TRIM FAULT advisory message and autopilot disconnect, flight crew commands for a nose-up trim resulted in a nose-down trim movement of the horizontal stabilizer instead.” In some events, “the horizontal stabilizer reached the full airplane nose-down trim position before the crew recognized the nature of the problem.”
The directive required revising the airplane flight manual to provide “instructions for an expanded pre-flight check of the pitch trim, trim malfunction procedures, and revised AP STAB TRIM FAIL caution and STAB TRIM FAULT advisory procedures.”