What happened
During a scheduled departure from Regina, Saskatchewan, an Air Canada McDonnell Douglas DC-9-32 was accelerating for takeoff when the crew experienced several loud bangs and significant vibrations throughout the airframe. At approximately 115 knots, the pilots, unable to identify the source of the disturbance through cockpit instrumentation, believed the aircraft had suffered tire failures. They promptly rejected the takeoff and brought the aircraft to a halt on the runway.
As the aircraft decelerated, the crew observed smoke appearing from the left side of the plane. Following emergency procedures, the captain ordered an evacuation. While the initial use of an emergency escape slide was hampered by high winds, passengers were successfully evacuated via the aircraft's airstairs. All 68 passengers and crew escaped the aircraft without injury, though many faced significant discomfort due to extreme windchill conditions while waiting for transport.
The investigation
Investigators examined the mechanical failure of the left engine, the performance of the aircraft's braking and electrical systems, and the maintenance history of the engine components. The investigation revealed that the engine's electrical failure, triggered by the component rupture, had disabled the anti-skid braking system and caused the flight recorders to cease operation. Furthermore, the investigation looked into why the structural flaw in the engine had not been identified during previous maintenance intervals.
Findings
- The left engine's combustion chamber outer case (CCOC) developed a crack originating at a rear flange bolt hole.
- This crack progressed through fatigue and intergranular fracture modes until the stresses of takeoff power caused the component to rupture.
- A misinterpretation of an airworthiness directive prevented the crack from being detected during previous maintenance shop visits.
- The rupture caused an immediate loss of engine power and a subsequent electrical failure that froze certain engine instrumentation readings.
- The loss of AC power and the activation of a cross-tie lockout prevented the pilots from receiving immediate cockpit warnings regarding the engine's declining performance.