What happened
On the night of 31 July 2008, an Air Canada Jazz Bombardier CL-600-2D15 (CRJ 705), registration C-FNJZ, was operating a flight from Toronto, Ontario, to Winnipeg, Manitoba. The aircraft was carrying 75 passengers and 4 crew members. After climbing to flight level 380, the captain reduced engine power to adjust the airspeed.
Over the following 17 minutes, the aircraft's airspeed gradually declined. During this period, the crew engaged in various tasks, including reprogramming the flight management system for weather deviations and interacting with cabin crew. Eventually, a loud rumbling and vibration were felt throughout the cabin. The autopilot disengaged, and the aircraft entered a stall condition, triggering the stick shaker and stick pusher. The pilot took control and attempted to recover, but the aircraft lost approximately 4,600 feet of altitude. During the recovery, the engines experienced an uncommanded power reduction, though they eventually recovered. One passenger sustained minor injuries during the descent. The aircraft landed safely in Winnipeg the following morning.
The investigation
Investigators examined the flight data from the digital flight data recorder (DFDR) and the engine's digital engine control (FADEC) units. The investigation established that the thrust setting selected by the pilot was insufficient to maintain the required cruise speed at the higher altitude, leading to a continuous decay in airspeed.
The investigation also looked into the crew's performance and training. While the captain had recently worked irregular shifts that could have increased fatigue risk, investigators determined that significant fatigue was unlikely at the exact time of the event. However, the investigation noted that the crew was distracted by cockpit activities and weather monitoring, which prevented them from noticing the airspeed decay. Furthermore, the investigation found that the crew's training did not sufficiently cover the specific buffet characteristics of the aircraft during high-altitude stalls.
Findings
- The engine power settings were set too low after leveling off at flight level 380, causing a steady reduction in airspeed.
- The crew was distracted by other tasks and failed to perform the routine instrument scans necessary to detect the airspeed loss.
- A lack of specific information regarding high-altitude stall characteristics prevented the crew from recognizing the impending stall.
- Inadequate training regarding high-altitude stall recovery contributed to pilot-induced oscillations during the recovery attempt.
- An uncommanded reduction in engine power during the stall further exacerbated the altitude loss.