What happened
On November 5, 2019, a Saab 340A, registration SP-KPV, was performing a scheduled flight from Kraków (UKKK) to Warsaw (EPWA). While cruising at flight level FL 220, the crew observed a "R ENG OIL PRESS" warning light, followed by a gradual decline in oil pressure.
In response to the pressure drop, the crew decided to divert to the nearest airport, Łódź (EPLB). Upon landing and conducting an engine inspection, maintenance personnel discovered an oil leak at the connection of an oil line supplying the turbine bearings. The engine's oil seals were replaced at the Łódź aerodrome, which successfully restored normal oil pressure. Following the flight to Warsaw, the CT7-5A2 turboprop engine's power turbine module was replaced as a preventive measure.
The investigation
The PKBWL investigation focused on determining why the oil leak occurred, particularly as the symptoms were identical to a previous incident. Following guidance from the engine manufacturer, investigators performed a borescope inspection of the ports and oil line attachment points.
The inspection revealed that remnants of old seals remained on the walls of the ports. These residues had caused the newly installed seals to fail during installation. The investigation found that while the operator had implemented a policy to replace all oil line seals annually, the cleaning of the ports was not being performed during routine line maintenance. According to the manufacturer, the specific procedure for cleaning and inspecting these ports is typically only required during major overhauls and is technically difficult to perform during standard line maintenance.
Findings
- The primary cause of the event was the failure of a new oil line seal due to damage caused by residual material from old seals left on the port walls.
- A contributing factor was the lack of an established procedure for inspecting and cleaning the ports during routine seal replacements.
Safety action
- Flight and maintenance personnel are to be briefed on the circumstances and causes of this occurrence.
- A request has been made to the manufacturer to develop a procedure for cleaning and inspecting these ports during both line and hangar maintenance.