The CFM56-7B engine design was susceptible to VSV bushing and shroud wear that can lead to internal mechanical damage and potential in-flight performance difficulties.
Safety bulletins to highlight potential for bushing/shroud wear, and operator performed fleet wide inspectoin.
The engine manufacturer has issued a number of service bulletins to operators highlighting the need for on-wing borescope inspection (S/B 72-0515) to look for inner shroud / J-hook wear. Additionally, the manufacturer has introduced new part numbers (S/B 72-0665 and S/B 72-0851) that appear to eliminate the root cause of the compressor surge.
The ATSB considers the safety action taken by the engine manufacturer adequately addresses this safety issue.
As a result of this incident, the operator approached the manufacturer to enquire if the recommended schedule of 24,000 TSN for the first inspection (as per S/B 72-0515) should be reviewed based on this occurrence. They were given a similar response to that provided to the ATSB. The operator was satisfied with this response, and further justified not changing the recommended schedule based on the findings of inspections performed on their fleet. The operator advised the ATSB that upon advice from CFMI, they were starting a campaign to replace the bushings and associated hardware on their owned engines (as per S/B 72-0581 and S/B 72-0665) at overhaul or whenever the engine had criteria that scheduled the next inspection at 800 hours or below (as per the service bulletin).
The operator further stated that they currently had 19 engines in service with new modified bushings factory installed and S/B 72-0581 had been incorporated to one engine at the shop visit. The majority of shop visits so far had been for lease engines (i.e., returned to the vendor well before 24,000 hours since new/repair), and as such, new pre-modification bushings had been installed unless the lease company specifically requested the hybrid or new metallic bushings. Since the incident, the operator has carried out a significant number of inspections in accordance with S/B 72-0515 and observed that the extent of VSV damage appeared to be greater on the high thrust engines.
As such, the operator has recently implemented Engine Plan Phase 2 which prioritises the replacement of the bushings and associated hardware of these high thrust engines, and includes a plan to replace the VSV components on over 40 engines within their inventory.
