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Western Australia: Engine malfunction involving Airbus Industrie A330-323

Christian Fernsby |
On 18 January 2018, a Malaysia Airlines Berhad (MAB) Airbus A330-323 aircraft registered 9M-MTM was operating a scheduled passenger flight designated MH122, which departed from Sydney, New South Wales, for Kuala Lumpur, Malaysia.

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On board were two flight crew, 10 cabin crew and 243 passengers. During the flight, the left engine malfunctioned, necessitating a diversion to Alice Springs where the aircraft landed safely.

The left engine, a Pratt and Whitney PW4170, had a third stage outer transition duct (OTD) segment liberation, which created a rise in exhaust gas temperature and significant turbulent airflow within the engine.

That in turn led to low pressure turbine blade failure, high vibration and compressor stall/surge events.

There have been a total of 16 similar events globally within the past 4 years that were all attributed to an engine modification, including five involving MAB aircraft. The modification increased the gas path temperature at the outer diameter of the flowpath, which led to distortion and liberation of OTD segments.

The engine manufacturer Pratt and Whitney had ceased production of PW4000-100 series engines for the Airbus A330 in July 2017. They have also redesigned the OTD to withstand higher temperatures.

The newly designed hardware will be available for purchase from November 2019 and recommended by service bulletin for installation at the customers’ discretion in affected engines when they are next scheduled for disassembly at an overhaul facility. Engines that have scheduled overhauls and repairs before the redesigned OTDs are available will receive a full new set of current OTDs.

This will remove ducts that were potentially exposed to elevated temperatures.

While the ATSB welcomed the availability of the redesigned OTD, as their fitment is not mandatory, safety recommendations were issued to Pratt and Whitney and the United States Federal Aviation Administration (FAA) to maximise fitment of the improved components.

MAB has implemented scheduled borescope inspections that are designed to identify precursors to an OTD failure. One of the five MAB events was identified while conducting a borescope inspection.

This incident is an example of an engine modification that had undesirable consequences. The negative effect of the redesign was identified by the engine manufacturer during analysis of a previously unseen failure mode in the PW4000-100 series engine.

The engine manufacturer has taken timely and significant safety action to redesign the outer transition duct. If fleet-wide replacement is implemented, the safety issue is expected to be addressed.

Finally, while the crew's response to the elevated temperature was in accordance with the required procedure, this occurrence highlights that significantly abnormal indications are often symptomatic of a developing problem. In such circumstances, the safest course of action is to discontinue the flight as soon as possible. â– 

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