What happened
On June 10, 2018, a student pilot undergoing PPL(A) training departed from EPBC airport in a Tecnam P20_JF for a planned flight to the Grądy (EPGY) area. Following a standard engine run-up where all parameters appeared normal, the aircraft took off from runway 10. During the initial climb, the crew noted that the rate of climb was lower than usual, which they initially attributed to high ambient temperatures of approximately 30°C.
As the aircraft completed its first turn, the crew sensed that engine power was lower than expected for the given temperature. After three minutes of flight, the cylinder head temperature (CHT) exceeded the maximum allowable limit, reaching approximately 140°C. The instructor took control of the aircraft and reduced engine power to the minimum level required to stabilize the temperature. The pilot then decided to return to the departure airport and notified Radio Babice of the intention. The aircraft landed safely on runway 10.
The investigation
The investigation focused on the technical condition of the engine cooling system. Upon inspection of the engine's cooling circuit, investigators identified a malfunction in the thermostat. The component was found to be opening the full flow of coolant to the radiator only when the coolant temperature reached 120°C, rather than the required 100°C.
Findings
- The direct cause of the overheating in the Rotax engine was a malfunctioning thermostat.
- The thermostat failed to open the coolant flow at the appropriate threshold, delaying the cooling process until the temperature reached 120°C.
- This delay prevented effective cooling of the cylinder heads, leading to temperatures exceeding the manufacturer's limits.