Aviation safety investigations & reports

Engine failure involving Airbus A330, 9M-XXE, near Carnarvon, Western Australia, on 25 June 2017

Investigation number:
AO-2017-066
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase

Final Report

Download final report
[Download  PDF: 939KB]
 

What happened

On 25 June 2017, an Airbus A330-343X aircraft, registered 9M-XXE and operated by AirAsia X departed Perth, Western Australia, on a scheduled passenger service to Kuala Lumpur, Malaysia. Approximately one hour into the flight, during a step change in altitude, the flight crew heard a metallic bang, significant vibration started through the airframe and ENG 1 [left] STALL warning was presented to the flight crew. The flight crew completed the relevant engine failure procedure and commenced a single‑engine return to Perth. Despite the flight crew’s attempts to reduce the vibration by varying the aircraft’s altitude and airspeed, the airframe continued to vibrate for the remainder of the return flight. After an event free landing at Perth, it was discovered that approximately three quarters of one fan blade was missing from the left engine.

What the ATSB found

The fan blade failed due to fatigue cracking located within a high stress region of the blade. Detailed structural analysis found that the primary drivers for the initiation of the fatigue crack were a small acute corner radius where the internal reinforcing membrane joins to the convex skin panel of the blade, together with an increased general stress state for the Trent 700 fan blades. This radius was not part of the design definition, but was an artefact of the blade manufacturing process. It was found that due to the complex manufacturing processes, there could be variation in this radius. The radius size could not be non-destructively measured, and as a result, the variation in this radius, and the effects it could have on the premature onset of fatigue cracking were not previously identified by the engine manufacturer.

As a result of a number of previous fan blade failures, the engine manufacturer had instigated a non-destructive inspection programme designed to detect internal cracking. Although the failed blade had been subjected to this inspection, the fatigue crack progressed to failure before its next scheduled inspection. As such, it was found that the inspection interval was too great to capture the crack that developed in this blade before it reached a critical size.

The flight crew decided to divert to Perth. While Perth was the nearest suitable aerodrome, at the time of the engine failure Learmonth was significantly closer. The fight crew’s decision to divert to Perth was influenced by the operator’s classification of Learmonth as an emergency aerodrome to be used in ‘dire emergency only’, a condition that the flight crew determined that was not applicable to their aircraft.

What's been done as a result

The engine manufacturer, Rolls-Royce, has taken a number of safety actions, including the revision of service bulletin RB.211-72-AH465 released in October 2017 to reduce the inspection interval from 2,400 to 1,200 cycles. This was supported by the release of European Aviation Safety Agency (EASA) Airworthiness Directive (AD) 2018-0188. Additionally, in November 2019, Rolls-Royce again revised RB.211-72- AH465 to introduce an enhanced inspection process thereby enabling the nominated inspection techniques to identify smaller cracks.

Rolls-Royce also issued service bulletin RB211-72-K096, to inspect a population of fan blades which showed defect indications at their last inspection, but were below the threshold for action. All of these blades were removed from service and were subjected to repeat inspections to confirm whether or not they were cracked. Additionally, it was intended that the blades would be sectioned (destructively examined) to confirm the nature of the indications. The data collected from these additional inspections was used by the manufacturer to refine the blade inspection process and introduce tighter acceptance limits.

Rolls-Royce have initiated a review of the design and manufacturing of the Trent 700 fan blade to address factors that could lead to failure and to make the blade more tolerant to the effects of the small acute corner radii. Additionally, Rolls-Royce is undertaking work to understand what manufacturing processes may influence the formation of the acute corner radii. This review activity has identified areas for improvement such as introducing local panel thickening to reduce blade panel stress in susceptible areas.

Safety message

During the complex manufacturing process of Rolls-Royce Trent 700 fan blades, a latent issue developed that was not realised for a number of years. This investigation demonstrates the importance for manufacturers of critical components, and regulators monitoring the manufacturers, to have systems in place to quickly identify core issues and put in place measurers to mitigate risk. This incident represents a good example of how manufacturers, through quick and positive actions can communicate engineering solutions and technical information to operators and maintenance providers through messages, service bulletins and service letters. It also demonstrates how regulatory authorities can work with manufacturers and incorporate mandatory safety solutions through communications including Airworthiness Directives.

Download final report
[Download  PDF: 939KB]
 
 
 

The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Additional details

Sources and submissions

Appendix A – Additional operational information

Appendix B – History of Trent 700 fan blade failures and in-service management

Safety Issues

Go to AO-2017-066-SI-01 - Go to AO-2017-066-SI-02 -

Fatigue cracking of Trent 700 fan blades

The Trent 700 blade manufacturing process produced a variation in internal membrane-to-panel acute corner geometry that, in combination with the inherent high level of blade panel stress, could lead to increased localised stresses in those corner areas and the initiation and propagation of fatigue cracking.

Safety issue details
Issue number: AO-2017-066-SI-01
Who it affects: Air transport operators whose aircraft are fitted with Trent 700 engines.
Status: Closed – Adequately addressed

Inspection period for blade cracking

The scheduled inspections recommended by Rolls-Royce to detect cracking in Trent 700 fan blades, were insufficient to detect early onset fatigue cracks in the membrane to panel bond before those cracks could progress to failure.

Safety issue details
Issue number: AO-2017-066-SI-02
Who it affects: Air transport operators whose aircraft are fitted with Trent 700 engines.
Status: Closed – Adequately addressed
General details
Date: 25 June 2017   Investigation status: Completed  
Time: 0816 WST   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): near Carnarvon   Investigation phase: Final report: Dissemination  
State: Western Australia   Occurrence type: Engine failure or malfunction  
Release date: 30 June 2020   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Airbus  
Aircraft model A330-343  
Aircraft registration 9M-XXE  
Serial number 1075  
Operator AirAsia X  
Type of operation Air Transport High Capacity  
Sector Jet  
Damage to aircraft Minor  
Departure point Perth, Western Australia  
Destination Kuala Lumpur, Malaysia  
Last update 30 June 2020