An in-flight upset following an autopilot disconnect aboard a Bombardier Challenger 300 seriously injured a cabin attendant near San Francisco on July 27, 2022, according to an NTSB final report released this week. The cause of the disconnect could not be determined, and cockpit voice recorder (CVR) data had been overwritten on a continuous loop.
Registered N557XJ, the Challenger 300 was operating a Part 91 positioning flight from San Francisco International Airport (KSFO) to Page, Arizona (KPGA). The aircraft departed at 12:30 p.m. with two pilots and one cabin attendant on board.
After taking off from KSFO, the autopilot had been engaged in the climb. When the aircraft was passing through 20,000 feet, two caution messages appeared on the crew alerting system: “AP STAB TRIM FAIL” and “AP HOLDING NOSE DOWN.” According to his statements, the pilot-in-command had assumed control from the second-in-command, and shortly thereafter the autopilot “disconnected on its own just as I was going to push the disconnect button.” The aircraft then pitched up rapidly.
Flight data recorder information showed vertical acceleration spiked from 0.985 g to 2.221 gs in less than one second, followed by -0.426 g and then 2.096 gs to 0.176 g in subsequent seconds. During these abrupt oscillations, the cabin attendant sustained serious injuries. The pilots regained control and continued without engaging autopilot to a safe landing at KSFO at 1:02 p.m.
Because the CVR had already overwritten the relevant portion of the flight, the NTSB could not confirm whether the crew completed the required checklist steps for the caution messages. Those procedures warned of possible abrupt changes in control forces upon autopilot disconnect and advised setting the seatbelt sign on and holding the flight controls firmly.
Since the aircraft was above 10,000 feet at the time of the upset, company policy permitted cabin attendants to move about the cabin. Thus, the attendant had unbelted and was not seated when the upset occurred. No indication was found that the PIC or SIC instructed her to return to her seat, which the NTSB noted as “an advisory that would have been prudent before an expected abrupt change in flight control forces.”
No mechanical anomalies were found in the autopilot system. All components passed postaccident testing, and the report noted that although the crew described the disconnect as automatic, the system did not log any fault that would have triggered it. The NTSB concluded that the autopilot was most likely disengaged through inadvertent pilot input, but the exact cause could not be determined.