What happened
During a scheduled domestic flight from Montreal International (Dorval) Airport to Toronto/Lester B. Pearson International Airport, an Airbus A320 operated by Air Canada experienced a significant mechanical failure. While the aircraft was climbing through flight level 280, the crew heard a loud bang. Following the noise, the crew noted a drop in the RPM of the No. 2 CFM56-5A engine, accompanied by an increase in exhaust gas temperature. The flight crew promptly shut down the engine and performed a single-engine landing at Toronto. Emergency response teams were on standby during the arrival, and there were no injuries or fatalities during the event.
The investigation
Following the incident, the failed engine was transported to Air Canada's maintenance facility in Montreal for a detailed teardown. Investigators discovered extensive internal damage spanning from the high pressure turbine (HPT) sections through to the low pressure turbine (LPT) sections. The inspection identified that a high pressure turbine blade had suffered a fatigue crack, which eventually led to the blade separating from the rotor assembly. This liberated blade fragment struck other engine components, triggering a chain reaction of overloads and temperature-related distress across the turbine sections.
Further examination focused on the high pressure turbine nozzle (HPTN) assembly, which was a repaired unit provided by CFMI for in-service evaluation. It was discovered that a portion of the nozzle guide vane material was missing. The investigation also scrutinized the communication of maintenance requirements between the manufacturer and the airline regarding the inspection of these specific repaired parts.
Findings
- The primary cause of the engine failure was the fatigue failure of a high pressure turbine blade during normal operation.
- A fatigue crack originated near the trailing edge of the HPT blade and progressed toward the leading edge.
- The failure was exacerbated by undetected damage to the repaired HPTN assembly, where a segment of the nozzle guide vane was missing.
- There was a failure in the communication of inspection protocols; the manufacturer's requirement for an 800-cycle repetitive inspection was not accurately conveyed to Air Canada.
- Air Canada maintenance staff incorrectly applied a 1,600-cycle inspection interval and did not perform the necessary borescope inspections of the nozzle guide vane convex surfaces.