What happened
On January 5, 2021, a Tecnam P2006T aircraft, registration CS-EAQ, was conducting a local training flight from Cascais Aerodrome (LPCS) toward the Sintra (LPST) area. Approximately three hours into the flight, the crew observed a drop in oil pressure in the number one Rotax 912S engine. After visually confirming an oil leak, the crew followed established checklist procedures and shut down the affected engine. The crew declared a "PAN-PAN" urgency to Air Traffic Control and returned to Cascais, successfully landing on the remaining engine at 11:45 UTC without further incident.
The investigation
The operator's Part 145 maintenance provider conducted an investigation into the cause of the leakage. During an engine run-up, technicians identified a leak near the ignition housing. Upon disassembly, the investigation revealed a damaged crankshaft oil seal retainer.
Findings
The investigation established that the primary cause of the in-flight oil leak was the failure of the crankshaft oil seal retainer due to wear caused by contact with the flywheel hub. This contact was a result of an improper installation of the retainer during an engine overhaul that had been completed less than 10 flight hours prior to the incident.
Several contributing factors were identified:
- The engine manual lacked sufficient installation details, specifically missing warnings or notes regarding the necessary alignment or eccentricity checks.
- The installation of the component requires a specialized tool (P/N: 877270); however, because the process is entirely manual, it is susceptible to misalignments that lack a secondary validation point.
- The overhaul training program available to the maintenance provider did not include specific details regarding this component's installation.
Safety action
The operator and maintenance providers have implemented the following measures:
- An inspection of the oil seal retainer installation and condition is being conducted on all currently active overhauled engines.
- The maintenance provider has updated its protocols to include more detailed installation instructions and a mandatory double-check inspection after the component is installed.
- The maintenance provider intends to consult the engine manufacturer to share these findings and seek further guidance to prevent recurrence.