What happened
On June 10, 2018, a Bombardier DHC-8-402 was performing a scheduled flight from Warsaw Chopin Airport (EPWA) to Budapest Ferenc Liszt International Airport (LHBP). Shortly after takeoff, at approximately 14:10 UTC, the flight crew noticed an increase in the oil temperature of the number two engine.
As the temperature reached 105°C, approaching the maximum limit of 107°C, the crew implemented the "HIGH OIL TEMPERATURE IN FLIGHT" checklist. Following the procedure, the crew reduced the power of the number two engine by 20%, which successfully lowered the oil temperature. The aircraft's climb was terminated at FL100. The crew decided to return to EPWA and requested a holding pattern to reduce the aircraft's weight for landing. After consuming approximately 150 kg of fuel, the aircraft commenced its approach and landed safely without further incident. The aircraft was subsequently handed over to maintenance personnel.
The investigation
The investigation focused on the mechanical cause of the temperature fluctuation. Technical inspections and testing were conducted to identify why the engine oil temperature had risen despite the crew's corrective actions.
Findings
- The primary cause of the incident was a malfunction of the engine number two oil cooler flap actuator (P/N 800600M03).
- Testing revealed that the oil cooler flap actuator had become stuck in the closed position, preventing adequate cooling of the engine oil.