Vietnam A332 at Melbourne on May 6th 2014, rejected takeoff due to uncontained engine failure
Last Update: June 1, 2017 / 21:51:00 GMT/Zulu time
The airport was closed for about one hour until the aircraft was moved off the runways.
Passengers reported hearing a pop sound like a tyre had blown and seeing streaks of flame out of the engine. The crew braked hard and stopped the aircraft.
Ground observers reported seeing lots of smoke from the aircraft and believed an engine fire had occurred.
The airport reported there had been an engine failure, debris of the engine was found on the runway. There had been no engine fire however, the smoke came off the tyres and was the result of hard braking by the crew.
The airline confirmed an "engineering malfunction" before takeoff.
On Dec 22nd 2014 the Australian Transportation Safety Board (ATSB) reported that the loss of power of the right hand engine was the result of blade failures on the 4th stage of the low pressure turbine. The ATSB stated: "One of those turbine blades was found to exhibit a fracture surface that appeared to be different to the remaining blades" and followed up stating that this blade was found to have fractured as result of high cycle fatigue cracking. The area of the crack initiation however could not be examined due to being obscured by rotational contact marks between blade and 4th stage nozzle guide vane clusters. Now the investigation "will focus on determining whether the turbine blade failed due to the failure of other upstream engine components or as a result of a defect within the blade itself."
On Jun 1st 2017 the ATSB released their final report concluding the probable causes of the incident were:
- The engine failure was initiated by the failure of a blade in stage four of the low-pressure turbine due to high-cycle fatigue cracking, which originated at the aerofoil’s leading edge.
- Cascading fracture and release of stage four turbine blades resulted in perforation of the low-pressure turbine front case and damage to the airframe from debris exiting via the exhaust duct.
- The flight crew’s handling of the rejected take-off reduced the risk of a runway excursion, preventing further damage to the aircraft and/or injury to passengers or crew.
The ATSB described the damage: "The engine cowls contained liberated LPT fragments that exited the engine radially via a 38 cm perforation in the LPT front case. There was no other damage associated with the LPT case rupture. LPT debris exited the exhaust duct and damaged the right inboard and outboard flaps, flap fairings, and the No. 2 spoiler. This damage did not affect the operation of any aircraft systems."
The ATSB analysed (quoted in full):
At 89 kt during the take-off roll, the aircraft’s right engine failed. The flight crew responded appropriately, successfully bringing the aircraft to a stop on the runway. Although the failure was uncontained, debris that exited via the low-pressure turbine (LPT) front case perforations was retained within the engine cowls. Debris exiting via the exhaust duct, damaged several flight control surfaces, however, this did not affect their operation.
This analysis will consider the engine failure sequence and the possible origins of the fatigue cracking in the stub of turbine blade 120 in stage four of the LPT. In addition, the high-cycle fatigue (HCF) cracking identified with 19 of the engines other stage four LPT blades will be discussed.
Turbine blade 120 failed as a result of HCF crack initiation and progression from the blade’s leading edge, to the point where the remaining material failed in overstress. The crack origin could not be examined for material anomaly or damage due to clashing damage from a number of stage four vane clusters. However, metal smearing over the HCF crack surface indicated that the cracking preceded the clashing damage. Despite being unable to determine the factors contributing to the cracking of blade 120, the extent of the cracking indicated that it was most likely the first blade to be released in the failure sequence.
The ATSB and Pratt and Whitney were not able to conclusively determine why the vane clusters contacted the fourth stage LPT blades. The case tear resulting from the failure of blade 120 was in the same location as the vane clusters that were identified as being loose and disengaged. It is possible that distortion and damage to the structure retaining the stage four vane clusters resulted in their contact with the rotating blades of the stage four LPT rotor. However, it is also possible that the vane clusters were displaced by an unidentified mechanism resulting in contact with the stage four blades and the initiation of HCF fatigue cracking in blade 120. In this scenario, further aft movement followed, resulting in the metal smearing observed on the fracture surface of blade 120.
In addition to blade 120, HCF cracking was found in 19 other stage four LPT blades. These blades exhibited minor cracking when compared to blade 120 but also exhibited similar clashing damage as sustained by blade 120. Less oxidisation on blade 18, compared to blade 120, indicated that the blade 18 fracture surface was exposed to the gas stream for less time than blade 120. Further, the HCF fracture surface on blade 18 was less advanced at the same distance from the blade’s leading edge compared to blade 120. This supports the cracking in blade 18 occurring later in the engine failure sequence than the cracking in blade 120, probably after the clashing commenced. It was therefore considered that the most likely initiator of the minor fatigue cracking in the 19 other blades resulted from their contact with the fourth stage vanes.
The ATSB did not identify any other similar failures that would indicate a systemic issue with the Pratt and Whitney PW4168A engines. No anomalies with the previous maintenance and repair of the LPT module or blade 120 were identified.
Recorded aircraft data indicated that the flight crew’s preparation of the aircraft for take-off was appropriate. During the rejected take-off, the flight crew responded effectively and communicated with the control tower and attending emergency services.
This article is published under license from Avherald.com. © of text by Avherald.com.
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