A diversion by a Malaysia Airlines Airbus A330 to Alice Springs has prompted a call by Australian safety investigators for a mandatory modification to engines powering some versions of the jet.
The Australian Transport Safety Bureau has issued safety recommendations to the US Federal Aviation Administration and engine manufacturer Pratt & Whitney calling on them to “maximize” a modification that would prevent a component failure of the PW4170 series engine.
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The recommendations stem from a January 18, 2018 incident in which a Malaysia Airlines Airbus A330-300 flying from Sydney to Kuala Lumpur diverted to Alice Springs in Central Australia due to a malfunctioning left engine.
ATSB investigators found that elevated temperatures had caused part of the third stage outer transition duct (OTD) to distort and fracture.
The large fractured section caused a blockage within the engine that created turbulent airflow, partially blocking a low-pressure turbine vane inlet stage and causing an increase in exhaust gas temperature.
The higher temperature led to low-pressure turbine blade failure, high vibration and compressor stall/surge events.
The ATSB found there had been 16 similar events globally within the past four years, all attributed to an increased thrust modification for the PW4000-100 engines called “Advanced 70”. This included five involving Malaysia Airlines aircraft.
Pratt & Whitney ceased producing the PW4000-100 series engines for the Airbus A330 in July 2017 but it has redesigned the OTD to withstand higher temperatures and the new hardware is available from this month.
Service bulletins will recommend the installation of the new ducts at the operator’s discretion but the ATSB would like to see the modifications made mandatory.
ATSB Director Transport Safety Stuart Macleod said that the ATSB welcomed the availability of the redesigned OTD
“This incident is an example of an engine modification that had undesirable consequences, and Pratt & Whitney has taken timely and significant safety action to redesign the outer transition duct,” ATSB director transport safety Stuart Macleod said.
“We have issued safety recommendations to Pratt & Whitney and to the United States Federal Aviation Administration, urging them to take action to maximise the fitment of the improved components,” Macleod said.
“If fleet-wide replacement is implemented, we expect this will address the safety issue.”
Malaysia Airlines told the ATSB it was conducting scheduled inspections to identify problems with the engines and would upgrade its fleet with the new OTD in stages.
The ATSB said the incident was also a reminder to pilots that the safest action when confronted with significantly abnormal indications in most instances was to land as soon as possible.
“Recognising that the crew’s response to the elevated temperature shortly after take-off was in accordance with the ECAM (electronic centralised aircraft monitoring) procedure, this occurrence highlights that significantly abnormal indications are often symptomatic of a developing problem,” Macleod said.
“In such circumstances, crews should give serious consideration to returning and landing the aircraft rather than continuing with the flight.”
