Engine fan blade failure leads to enhanced inspection processes

A fan blade failure in an Airbus A330's Rolls-Royce Trent 700 engine

A fan blade failure in an Airbus A330’s Rolls-Royce Trent 700 engine due to a fatigue crack has led to enhanced inspection processes and technical solutions that reduce the likelihood of future similar occurrences, a new ATSB investigation report details.

In June 2017, an AirAsia X Airbus A330-300 sustained an engine failure while operating a scheduled passenger flight from Perth to Kuala Lumpur. About one hour into the flight, during a step change in altitude, the flight crew heard a metallic bang, significant vibrations could be felt through the airframe, and an ‘ENG 1 STALL’ warning was triggered.

The flight crew executed the relevant engine malfunction procedure and commenced a single-engine return to Perth. While the airframe vibrations continued during the return to Perth, the aircraft landed there without further incident.

On the ground an inspection found about three quarters of one fan blade was missing from the failed left engine.

Subsequent detailed structural analysis determined that the failure of the fan blade was due to a fatigue crack which had initiated from within the blade’s internal structure where an internal reinforcing membrane joins to the blade’s convex skin panel.

Detailed structural analysis determined that the failure of the fan blade was due to a fatigue crack.

The report notes the blade manufacturing process produced a variation in the 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.

The investigation also determined that 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.

Rolls-Royce have taken a number of proactive safety actions to mitigate future blade failures. These include reviewing the design and manufacturing of the Trent 700 fan blade and releasing service bulletins covering engine inspections (one of which was supported by a European Aviation Safety Agency (EASA) issued Airworthiness Directive).

The engine manufacturer also introduced new a control system modification, designed to shut the engine down quickly when fan blade failure event occurs to reduce damage to the fan shaft.

During the complex manufacturing process of Trent 700 fan blades, a latent issue developed that was not realised for a number of years, the investigation notes. This 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 measures to mitigate risk.

The report also notes that 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.

You can find here the investigation report AO-2017-066: Engine failure involving Airbus A330, 9M-XXE, near Carnarvon, Western Australia, on 25 June 2017

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