ATSB issues safety advisory notice against CFM56-5 and CFM56-7 engines

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The Australian Transport Safety Bureau (ATSB) has warned operators of CFM International CFM56-5 and CFM56-7 engines to be aware of premature wear that may precipitate engine failure.

The bureau wishes to "draw the attention of all operators of CFM56-7 and CFM56-5 engines and their variants to the safety issues identified by this investigation," says the ATSB in its safety advisory notice.

"In particular, operators should be aware of the potential for premature wear within the compressor variable stator vane bushings and shroud to develop to levels where it may precipitate the failure of the engine while in service, and within a time-frame that is less than the minimum threshold for the initial inspection for the problem."

"Operators are encouraged to review their procedures to ensure an appropriate awareness of the issues among maintenance personnel," it adds.

The CFM56 is found on Airbus A320s and Boeing 737s.

The ATSB launched its investigation after a 20 August 2009 incident in which a Virgin Blue Boeing 737-800, local registration VH-VOC, had to return to Launceston Airport because a compressor surge and damage to the left engine.

"The compressor surge and damage to the left engine was the result of advanced variable stator vane bushing/shroud wear, which caused a seal retainer to dislodge from the inner shroud segment and move into the compressor gas path," says the ATSB.

"The liberated seal segments then progressed downstream, causing significant damage to the remaining stages, resulting in loss of compressor efficiency," it says.

The ATSB says the engine manufacturer has responded by issuing a number of service bulletins to operators highlighting the need for on-wing borescope inspection to look for inner shroud and j-hook wear.

It also introduced new part numbers that appear to eliminate the cause Of the compressor surge, says the bureau.

As a consequence, the ATSB considers that the safety action, taken by CFM International, adequately addresses this safety issue, it adds.