What happened
On May 26, 2018, a crew from the Zielona Góra branch completed a medical transport mission to Nowa Sól, landing safely at the base. During a routine inspection of the main rotor prior to a subsequent mission, the commander heard unusual cracking noises originating from the fenestron area. The pilot immediately notified the Technical Coordination Center (CKT).
To investigate the source of the noise, the CKT directed the crew to perform a cold engine start. Following this procedure, an audio recording of the sounds was transmitted to the technical center for analysis. Consequently, the EC 135 P2+ was grounded and withdrawn from further flight operations.
The investigation
Technical personnel from the Szczecin maintenance station performed a diagnostic inspection of the aircraft. The investigation established that the abnormal sounds were caused by the overheating of the bearings on the long shaft, which transmits power from the main gearbox to the fenestron. To rectify the issue, a mechanic replaced five bearings within the drive shaft supports with new components. A ground test was subsequently performed, which yielded a positive result, allowing the aircraft to return to service.
Findings
- The probable cause of the incident was the operational wear of the bearings on the long shaft connecting the main gearbox to the fenestron.