What happened
On September 26, 2020, at approximately 15:00 UTC, a Cessna C525A CJ2, registration SP-KCK, was preparing for a flight from Nicea (LFMN) to Stockholm-Arlanda (ESSA). During the start-up sequence of the left engine, the flight crew observed that the low-pressure turbine RPM failed to increase. The crew immediately aborted the engine start attempt. Upon attempting to manually rotate the engine fan, the crew found that movement was impossible, indicating a mechanical seizure.
Following consultations with the operator's maintenance organization (CAMO), technical staff, and the engine manufacturer, a technician from the Cessna Service Center in Paris was dispatched to Nicea to perform a borescope inspection. While the inspection revealed no visible damage to the compressor or turbine blades, the technician suspected damage within the low-pressure turbine section. The engine manufacturer, Williams International (producer of the FJ44-2C engine), subsequently advised the operator that the engine required disassembly and overhaul at their facility.
The investigation
The investigation focused on the engine disassembly process and the subsequent communication regarding the failure. During disassembly, it was discovered that the engine seizure was caused by a crack in the low-pressure turbine first-stage guide vane case (P/N 115316).
The investigation highlighted significant issues regarding the information provided by the engine manufacturer. The disassembly report provided to the operator was noted as being overly brief, lacking detailed descriptions of the damage, specific locations of the failure, or photographic evidence. This lack of transparency led to operational concerns regarding the continued airworthiness of similar engines. The manufacturer declined to provide more granular details, citing the protection of intellectual property.
To resolve these uncertainties, the PKBWL requested assistance from the NTSB. The NTSB concluded that the manufacturer could have provided more detailed explanations to address the operator's concerns without compromising proprietary design information. Furthermore, the investigation identified that the existing Service Bulletin lacked sufficient information regarding differences between various guide vane assembly types, leading to conflicting manufacturer positions regarding part interchangeability.