What happened
On December 13, 2018, an ATR 72-202 arrived at Warsaw Chopin Airport (EPWA). Following the aircraft's arrival, maintenance personnel conducted an inspection and discovered an oil leak originating from the left propeller area.
Detailed inspections of the propeller assembly revealed several significant mechanical discrepancies. The findings included an oil leak from the propeller shaft seal, as well as several issues regarding the fasteners connecting the propeller hub to the engine shaft. Specifically, the nuts on the bolts securing the hub were not tightened to the required torque, and the threads on two of these bolts were found to be damaged. Furthermore, the inspection identified cracks and material loss on 16 hexagonal nuts used in the hub-to-shaft assembly. The investigation also noted the absence of a slip ring between the actuator and the propeller hub.
The investigation
The investigation, conducted by the aircraft operator, established that the propeller assembly had been installed by an external maintenance organization. The technical review focused on the assembly process and the integrity of the components involved in the propeller-to-engine shaft connection.
Findings
The investigation determined that the improper installation of the propeller on the engine shaft in violation of the aircraft maintenance manual was the primary cause of the incident. The mechanical failures and leaks were direct results of the non-compliant assembly procedures performed by the external service provider.