What happened
Shortly after departing from Meekatharra Airport, the pilot of a VH-OWS observed engine oil leaking from the engine and coating the aircraft's windscreen. Recognizing the hazard, the pilot immediately initiated a return to the airport, where the aircraft was brought to a safe landing.
The investigation
Investigators determined that the leak originated from the propeller shaft seal assembly. The investigation revealed that the seal had been replaced the previous day, but the components were not installed in the proper sequence. Specifically, a half flat spacer was positioned forward of the seal rather than aft. This incorrect placement caused the seal to be compressed against the seal runner, leading to abnormal wear caused by friction during rotation.
To perform the assembly, the engineer consulted the engine manufacturer's illustrated parts catalogue (IPC), which contained an indicative but technically incorrect diagram. While the engineer did refer to the engine maintenance manual (EMM), he failed to notice that the assembly procedure and diagram in the EMM differed from those in the IPC. Furthermore, the engineer relied on his memory of the disassembly process rather than strictly following the manual's instructions.
Findings
- The propeller shaft seal assembly was incorrectly configured, with the spacer placed in the wrong position.
- The engineer utilized an incorrect diagram from the IPC instead of the correct sequence provided in the EMM.
- The engineer's reliance on memory during reassembly was a contributing factor.
- The engineer's ability to recall the correct order may have been compromised by fatigue resulting from disrupted sleep and extended working hours.