What happened
During a scheduled maintenance procedure on 5 October 2016, inspectors identified four fatigue cracks located on the ribs of the No. 2 engine pylon strut. The components were found to be in compliance with all manufacturer material specifications and engineering drawings, with no other obvious defects present at the time of discovery.
The investigation
The investigation focused on the origin of the fatigue cracks and the structural integrity of the pylon. Investigators examined the possibility that a previous engine event might have caused the damage, noting that the No. 2 engine had experienced a seizure approximately six months before the cracks were found. This seizure had transmitted significant torque and vibratory loads into the pylon structure. However, metallurgical analysis of the fracture origins showed no signs of alloy tearing or plastic deformation, suggesting the seizure was not a direct cause of the cracking.
An analysis by the manufacturer confirmed that the pylon maintained enough residual strength to handle all required load cases, meaning the structural integrity of the aircraft was not compromised.
Findings
- The cracks likely resulted from exposure to vibratory loading occurring during standard engine operations.
- The accumulation of flight cycles and airframe hours over the aircraft's service life may have contributed to the development of the cracks.
- The inspection regime utilized by Qantas, which employed a 24-month interval, was more frequent than the manufacturer's recommended 48-month interval. This shortened schedule allowed for the detection of the defects before they reached a level that posed a safety risk.