A medium-sized bird and a series of unfortunate events have been blamed for an AirAsia X engine failure on the Queensland Gold Coast last year.
The culprit was a masked lapwing, a bird usually weighing between 230 and 400 gms and one the Rolls-Royce Trent 700 engine was designed to handle.
But testing by the engine manufacturer found a rare combination of factors caused a fan blade tip to fracture on the AirAsia X A330 as it took off on July 3, 2017 with 357 passengers and crew on board.
READ: AirAsia X to add first aircraft since 2015.
The crew was alerted to an engine stall and a loud banging noise shortly after take-off, according to a report rleased Wednesday by the Australian Transport Safety Bureau. They followed procedures and made a PAN PAN call to alert authorities there was a problem.
The pilots upgraded the call to a MAYDAY and requested a diversion to Brisbane Airport after receiving an alert there was an engine failure and a fire. The plane landed safely and there were no injuries.
Bird remains found on the runway were found not have passed through the engine but a DNA analysis of organic material found on various parts during a detailed inspection by Rolls-Royce discovered that at least one lapwing did.
The manufacturer concluded that multiple birds had hit the fan but the damage at the tip of the fan blade was due to a single bird.
It found of material from the fan blade tip caused the fan to run out of balance when the engine was at take-off thrust and the combination of the two damaged the fan rear seal.
Fragments of the seal likely entered the engine core, causing significant damage to the compressors and resulting in a series of compressor stalls.
A problem with an oil seal as a result of a bolt unwinding prompted in an oil leak and this ignited either from frictional heat generated by seals rubbing or components moving.
The resulting fire between the front bearing housing and fan disc caused failure and melting of aluminum alloy components but was not enough to damage structural components with higher melting points.
Rolls told investigators the AirAsia X event had not been experienced during the medium bird certification test when eight birds of at least 680 gms (1.5lbs) were fired into the engine at least 168 knots.
Nor did it undermine the capability of the Trent 700 engine, which had experienced more than 430 reported birdstrikes with only five resulting in fan material loss, it added.
ATSB executive director of transport safety Nat Nagy said it was rare for a bird strike to lead to an engine failure.
“Scenario testing by the manufacturer indicates this occurrence was a rare combination of the height of the fan blade at which the birdstrike occurred, the angle the bird struck the fan blade and the aircraft and engine speeds,” he said.
“It is very unlikely a similar event would reoccur, and extremely unlikely that it would occur on multiple engines at the same time.”
Reviews of the flight data and cockpit voice recorders showed the flight crew effectively managed the unusual situation.
“Airlines still need to ensure they have robust emergency procedures in place, supported by training and regular proficiency checks, to help flight crews respond appropriately to events like this,” Nagy said.
“By following their procedures, having good communication and falling back on their training, this flight crew managed to respond appropriately and produce a safe outcome from such a rare and unexpected event,” Nagy said.
AirAsia welcomed the report and the findings on its flight crew.
“This was an unprecedented incident and, as the report confirms, the crew were well-trained and prepared to manage this rare and unexpected situation,’’ spokesman Kris Taute said.
“Safety at AirAsia has always been our number one priority. As part of this commitment, AirAsia X recently attained its Operational Safety Audit (IOSA) registration for the third consecutive time.
“IOSA certification is regarded by the industry as the global benchmark for safety management.”
One of the most dramatic examples of a bird strike occurred with 2009’s “Miracle on the Hudson” when a USAirways Airbus A320 struck a flock of Canada geese after take-off from New York and lost all engine power.
Pilots Chesley Sullenberger and Jeffrey Skiles glided the plane to ditch in the Hudson River with no loss of life.
