The European Aviation Safety Agency issued a safety information bulletin alerting operators of Airbus A320 family aircraft equipped with CFM International CFM56-5A engines to an unexplained anomaly that on 30 June caused a departing aircraft to return to the airport.
CFM says there are more than 1,100 of the engines in service built specifically for the A320 series, with a cumulative total of 32 million flight hours and dispatch reliability of more than 99.9%. The engine has been offered on the A319 and A320 models, but not the A318 or A321.
According to the EASA report, issued on 30 July, a CFM56-5A-powered A320 family aircraft of an undisclosed operator experienced a stall and in-flight shutdown with an accompanying exhaust gas temperature (EGT) over limit and high vibrations during take-off.
Mechanics conducting a borescope inspection after the incident found that the engine's low-pressure turbine (LPT) section had been damaged, with several blades broken off. The engine had accumulated 39,808h and 30,980 cycles since new but only 21h and 15 cycles since its last shop visit.
Upon disassembly, a preliminary examination of the LPT and high-pressure turbine (HPT) revealed overheating, suggesting a "cooling deficiency by hot gas ingestion into the turbine rotor air cooling system", says EASA. "The cause of this overheat condition has not yet been identified."
The disk, identified as the LPT stage 1 disk, had fractured with "one full radial separation", says EASA. "The disk remained in one piece, expanded but fully contained."
EASA, the US Federal Aviation Administration and CFM continue to investigate the maintenance shop that performed the most recent work, and the airline involved. "This investigation will determine whether any recommendations or mandatory actions are necessary."
Source: Flight International
