Incident Overview
On 5 November 2019, a SAAB 340A aircraft, registered as SP-KPV, was conducting a flight from UKKK to EPWA. During cruise at flight level 220, the "R ENG OIL PRESS" warning light illuminated. After several minutes, the crew observed a gradual decrease in oil pressure. The decision was made to divert to the nearest suitable airport, EPLB in Łódź.
Findings and Repairs
Upon engine inspection at EPLB, an oil leak was detected at the connection of the oil supply line to the turbine bearings, located in a dedicated port. The operator replaced the complete set of seals on the oil lines: one supply line to the turbine bearings and three oil scavenge lines from the oil sump. After seal replacement, no oil leak was observed and oil pressure returned to normal. Following arrival at EPWA, the engine's CT7-5A2 turboprop turbine module was replaced as a preventive measure.
Investigation and Root Cause
Because the symptoms were identical to a previous incident (No. 4738/19), the operator contacted the manufacturer. The manufacturer directed a borescope inspection of the ports where the oil lines attach. The inspection revealed remnants of old rubber seals adhering to the port walls (see Fig. 2). These remnants had damaged the new seals during installation after the earlier incident. The operator had introduced a practice of annual replacement of the entire seal set on oil lines several years earlier, based on operational experience. However, the seal replacements were performed without prior cleaning of the ports, as there was no procedure for such cleaning under line maintenance conditions. According to manufacturer specifications, port inspection, cleaning, and seal replacement are only performed during major overhauls using a manufacturer-developed procedure. That procedure is technically not feasible during line maintenance.
Corrective Actions
To prevent recurrence, the engine was removed from the aircraft and will undergo inspection and rectification after the manufacturer issues a new procedure for port inspection and cleaning.
Probable Cause
The cause of the incident was a loss of seal integrity in the oil line connection to the oil sump, due to damage of the new seal by remnants of the old seal on the port walls.
Contributing Circumstance
A contributing circumstance was the lack of a procedure for inspecting and cleaning the ports when seal replacement is necessary.
Recommendations
1. Inform flight and maintenance personnel of the circumstances and causes of the incident. 2. Request the manufacturer to develop a procedure for cleaning ports during line and hangar maintenance.