Air New Zealand (ANZ) is investigating an incident involving a Boeing 767-300, which had its left hand General Electric CF6-80C2 engine shut down after an engine problem.
ANZ had earlier said the engine problem could be due to a bird strike but has since ruled this out.
The flight crew operating the aircraft, which was flying from Auckland to Perth on 9 June, had reduced take-off thrust as normal when the aircraft was airborne. "But at this time there was an interruption to the airflow through the left hand engine which caused the flare seen from the rear of the engine," said the Star Alliance carrier. This change in airflow had resulted in "a similar reaction to that of a car backfiring", said ANZ's general manager airline operations and chief pilot David Morgan.
The pilots further reduced thrust as required by procedure and the left hand engine began "operating normally", it added. "Regardless of the engine returning to normal operating levels, the pilots followed Air New Zealand's conservative operating procedures and undertook a precautionary engine shut down before returning to the airport so the cause of the airflow disruption could be determined," said the airline.
The flight crew returned to Auckland, where the aircraft landed without incident.
ANZ had said immediately after the incident that a bird strike could have caused the engine problem but said investigations have since showed no evidence of this. There is no damage to the engine. "The unit responsible for the control of airflow through the engine has been removed and will be sent to the manufacturer for testing. We have replaced the unit and will now undertake engine tests in conjunction with the engine manufacturer GE," said Morgan.
The 206 passengers on board the flight were accommodated in hotels before they flew out on another aircraft today, and have since arrived in Perth.