What happened
On 25 June 2017, an AirAsia X Airbus A330-343X, registration 9M-XXE, was performing a scheduled passenger flight from Perth, Western Australia, to Kuala Lumpur, Malaysia. During a planned climb from flight level 380 to 400, the flight crew heard a loud metallic bang followed by significant airframe vibrations. The aircraft's monitoring system issued alerts for an engine stall and a control system fault on the left engine.
Following established procedures, the crew shut down the left engine. Although the crew attempted to mitigate the vibrations by adjusting the aircraft's airspeed and altitude, the shaking persisted throughout the descent. During the return flight, cabin crew reported seeing black smoke emanating from the engine, prompting the pilots to discharge a fire extinguisher bottle. The aircraft performed an event-free landing at Perth. A subsequent inspection revealed that approximately three quarters of one fan blade was missing from the left engine.
The investigation
Investigators performed a detailed structural analysis of the failed fan blade. The examination focused on the fatigue crack located within a high-stress area of the blade. The investigation also reviewed the maintenance history of the engine and the effectiveness of existing inspection protocols implemented by the manufacturer, Rolls-Royce.
Findings
- The failure was caused by a fatigue crack originating from a small, acute corner radius where the internal reinforcing membrane meets the convex skin panel of the blade.
- This specific radius was not a design requirement but was an unintended byproduct of the complex manufacturing process.
- Because the size of this radius could not be measured using non-destructive methods, the manufacturer had not previously identified its potential to trigger premature fatigue.
- While an inspection program was in place to detect internal cracking, the inspection interval was too infrequent to catch the crack before it reached a critical, failure-inducing size.
- The crew's decision to divert to Perth, rather than the closer Learmonth Airport, was based on the operator's policy regarding emergency aerodromes.
Safety action
Following the incident, Rolls-Royce implemented several measures to enhance safety:
- The inspection interval for ultrasonic testing was reduced from 2,400 to 1,200 cycles.
- An enhanced inspection process was introduced to improve the detection of smaller cracks.
- A service bulletin was issued to inspect blades that showed minor indications during previous checks.
- The manufacturer initiated a design review of the Trent 700 fan blade to improve tolerance to manufacturing variations and reduce stress in susceptible areas.