Aviation safety investigations & reports

Engine malfunction involving Airbus Industrie A330-323, registered 9M-MTM, 37 km north of Curtin Airfield, Western Australia on 18 January 2018

Investigation number:
AO-2018-007
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase

Final Report

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What happened

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. 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.

What the ATSB found

The left engine, a Pratt & 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.

What's been done as a result

The engine manufacturer Pratt & 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 & 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.

Safety message

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.

Pratt & Whitney PW4170 gas turbine engine

Pratt & Whitney PW4170 gas turbine engine. Source: Pratt & Whitney, modified by the ATSB

Source: Pratt & Whitney, modified by the ATSB

Download final report
[Download  PDF: 477KB]
 
 
 

The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions

Safety Issue

Go to AO-2018-007-SI-01 -

Advantage 70 engine modification

There were a total of 16 engine malfunction events globally over a 4-year period attributed to modification of the Advantage 70™ engine. The modification increased the engine outer duct gas path temperature, which led to distortion and liberation of the outer transition duct segments.

Safety issue details
Issue number: AO-2018-007-SI-01
Who it affects: All operators of Airbus A330 aircraft fitted with Pratt & Whitney PW4170 engines or Advantage 70™ engine modification.
Status: Safety action pending
General details
Date: 18 January 2018   Investigation status: Completed  
Time: 1500 WSuT   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): Near Curtin Airport   Investigation phase: Final report: Dissemination  
State: Western Australia   Occurrence type: Engine failure or malfunction  
Release date: 06 November 2019   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Airbus  
Aircraft model A333  
Aircraft registration 9M-MTM  
Serial number 1431  
Operator Malaysia Airlines  
Type of operation Air Transport High Capacity  
Sector Jet  
Damage to aircraft Minor  
Departure point Sydney, NSW  
Destination Kuala Lumpur, Malaysia  
Last update 06 November 2019