A 2022 CFM Leap-1A in-flight engine shutdown traced to non-conforming parts has prompted the FAA to plan mandatory replacements of the affected components based on the manufacturer’s recommendations.
The agency’s proposed fix is replacing the affected parts, high pressure turbine (HPT) rotor interstage seals, at the next engine shop visit, a draft rule published Oct. 2 said. A “shop visit” involves separating “major mating engine flanges” for maintenance, the FAA said. The draft directive is based on a CFM service bulletin issue in June.
The swaps must be done before the parts reach their design limits of 11,100 cycles since new for commercial operators, or 9,700 cycles since new for engines on corporate jets. CFM’s recommended fix does not reduce the life limits.
“We expect the vast majority of the seals to be replaced during already-planned shop visits, minimizing disruption for our customers,” CFM said in a statement.
The company said about 500 seals are affected and about 25% have been removed from service.
The problem was discovered during the probe of a May 19, 2022, in-flight engine shutdown involving an Air India Airbus A320neo near Mumbai. A final Director General of Civil Aviation (DGCA) report on the incident published in late 2023 said CFM narrowed down the non-conformance to “inadequate peen coverage” during the shot-peening process used to make metal parts more resistant to cracking and fatigue.
“While CFM determined the root cause to be specific to a single supplier of this part, the company has implemented corrective actions with all suppliers of this part,” the company’s statement said. Information in the DCGA report refers to the supplier as “Paradigm.”
The incident engine had accumulated 6,596 cycles since new and 3,242 since its most recent shop visit when the seal failed, the DGCA report said.
The issue only affects Leap-1As that power some A320neo-family aircraft.
The FAA draft rule said the seal failed due to a combination of two issues: the part’s non-conforming surface and friction-related stress.
“Ground inspection following the event found that several low-pressure turbine blades had broken and metal had entered the exhaust,” the draft rule said. “A manufacturer investigation later determined that the aft arm of the HPT rotor interstage seal had failed due to a non-conforming surface condition in the fillet area coupled with higher-than-expected operating stress due to friction.”
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