What happened
On August 18, 2018, at approximately 23:46 UTC, a Fokker 50 (registration JU-8883) was performing a flight from Ulaanbaatar to Chinggis Khaan International Airport. During the flight, the crew observed significant torque fluctuations on the right engine. Following the detection of these fluctuations, the pilot initiated the single-engine procedure and shut down the right engine. The aircraft continued the flight on the remaining engine and landed safely at the destination airport.
The investigation
The investigation focused on the technical failure of the engine components and the subsequent engine shutdown. Investigators examined the Multi-Function Fuel Control Unit (MFCU) and the engine's performance data. The examination of the MFCU (part number 3244858-24) revealed that the driveshaft cap bearing (part number 1590/1600) had experienced wear. Specifically, the investigation established that the bearing's outer diameter had worn down to 1530 microns, while the inner diameter had worn to 1580 microns, deviating from the required specifications.
Findings
- The primary cause of the engine shutdown was the failure of the driveshaft cap bearing within the MFCU.
- The bearing wear led to the observed torque fluctuations on the right engine.
- A contributing factor was the presence of a soft time limit on the MFCU component, which allowed the degraded part to remain in service.
- The investigation also noted that the engine shutdown was executed in accordance with established single-engine procedures.