Multiple EICAS Alerts Preceded Fatal Challenger In-flight Upset

 - March 28, 2023, 11:25 AM
A Bombardier Challeger 300 suffered an in-flight upset that occurred after a pilot responded to one of multiple EICAS messages. (Photo: Twitter)

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. They also used the incorrect checklist in the air (PRI STAB TRIM FAIL) instead of the checklist for what the EICAS showed (AP STAB TRIM FAIL).

During the first takeoff attempt, the second-in-command (SIC) noticed an airspeed miscompare and the pilot-in-command (PIC) aborted the takeoff. After shutting down the left engine, the SIC exited the airplane and removed a pitot tube cover from the right side pitot probe. After restarting the engine and seeing the RUDDER LIMIT FAULT advisory message, according to the report, "The PIC reported that he attempted two ground avionics 'stall tests' to clear the message, as he had received this advisory message in past ground operations, however, the tests did not clear the annunciation. The flight was continued given that the message was an advisory, and not a caution or warning." During the second takeoff, the V-speeds were not set and displaying on the primary flight display, and "The SIC called V1 and rotate at 116 knots from memory and the PIC entered the climb without issue." 

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 twinjet 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 PRI STAB TRIM FAIL checklist (not the AP STAB TRIM FAIL checklist), which initially called for the stabilizer trim switch to be turned off.  The AP STAB TRIM FAIL checklist calls for the pilots to turn on the smoking/seatbelt light.

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 +3.8 g.

The airplane subsequently entered a negative vertical acceleration to approximately -2.3 g and pitched up again to about 20 degrees and +4.2 g. The stick pusher activated during this pitch-up and vertical acceleration lowered to about +2.2 g. 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.”

According to the NTSB preliminary report, both pilots were type rated as PIC in the Challenger 300 in October 2022. The PIC had more than 5,000 hours total and 88 time in type, while the SIC had more than 8,000 hours total and 78 in type. The aircraft was managed by Executive Flight Services, according to the report, on behalf of the owner Conexon.