What happened
On December 24, 1999, an Air Canada Airbus A3-20-211 was performing a scheduled passenger service from Calgary, Alberta, to Vancouver, British Columbia. While cruising at 35,000 feet near Revelstoke, British Columbia, the aircraft's No. 2 engine experienced two surges. Following these fluctuations, the pilot requested a return to Calgary via a gradual descent.
During the approach to Calgary, as the crew extended the flaps and landing gear, the engine power increased, leading to a third surge in the No. 2 engine at approximately 60 per cent power. The pilot responded by reducing thrust on the affected engine to idle, increasing thrust on the No. 1 engine, and declaring an emergency. Upon touchdown, an aircraft firefighting vehicle observed a 10-foot flame originating from the No. 2 engine. The aircraft stopped on a taxiway, prompting the crew to command an evacuation. Five of the six emergency slides were deployed. There were no injuries to the passengers or crew, and no external damage was sustained by the aircraft.
The investigation
The investigation focused on the mechanical failure of the CFM56-5A1 engine and the effectiveness of the emergency response. Laboratory analysis of the No. 2 engine revealed that the No. 4 bearing had failed. This failure caused the engine components to rotate at inconsistent speeds, resulting in airflow reversal and the initial surges. The subsequent destruction of an aft sump oil seal allowed oil to enter the hot exhaust duct, which ignited during the landing rollout.
Investigators also examined the communication between the aircraft firefighting (AFF) personnel and the flight crew. It was noted that the AFF vehicle, "Red Five," attempted to contact the crew using the aircraft's registration number rather than its call sign, which likely prevented the crew from noticing the transmission. Additionally, the investigation looked into the cabin environment during evacuation, noting that the interior was dark and the emergency lighting system's activation was difficult to verify due to low light and the position of the switch.
Findings
- The primary cause of the engine surge was the failure of the No. 4 bearing due to a lack of lubrication.
- The engine's power increase during the landing approach contributed to the complete bearing failure and the subsequent exhaust duct fire.
- Communication guidance in the Canadian Aviation Regulations for AFF personnel and flight crews was found to be limited, specifically regarding effective contact during ground emergencies.
- The lack of illumination or clear marking on the emergency light switch on the flight attendant panel could negatively impact cabin safety during night or low-light evacuations.