What happened
On 20 June 2012, an Air New Zealand Airbus A320 was performing a landing at Wellington International Airport when a black-backed gull was ingested into the right engine. Despite the strike, the aircraft completed its landing without further incident. Following the event, maintenance engineers inspected the engine according to the manufacturer's manual. Because no immediate damage was visible, the aircraft was permitted to continue operating under a specific allowance for up to 10 flight hours or one additional sector, pending a full borescope inspection.
The aircraft subsequently flew to Auckland International Airport carrying 172 people, including five crew members. During the approach to land in Auckland, the same engine experienced a failure. The captain responded by reducing thrust to idle and proceeded with the landing. Although the engine sustained internal damage, it remained operational through the landing phase.
The investigation
Investigators examined the engine components to determine the sequence of the failure. The inspection revealed that the initial bird ingestion had caused internal damage, specifically resulting in a crack within a third-stage compressor blade. The investigation established that the crack expanded due to the mechanical stresses of continued operation. Eventually, the blade fractured completely, leading to a cascade of damage as the broken pieces moved through subsequent compressor stages.
Additionally, the Commission investigated the communication of engine health data. While the aircraft's systems are designed to automatically send reports to the operator's maintenance control center, the critical data regarding the engine's condition failed to reach the control center during this flight. The investigation confirmed that the issues preventing these reports from being received have since been resolved.
Findings
- The engine failure was caused by the progressive growth of a crack in a compressor blade, which originated from the initial bird strike.
- The aircraft was operating under a continued operating allowance that permitted flight before a full borescope inspection could be performed.
- Automated engine health reports failed to reach the maintenance operations control center during the flight.
- Bird management practices at Wellington International Airport were found to be in line with industry best practices.