What happened
On 17 February 2025, a Tecnam P2/006T, registration SP-SUT, was conducting a professional pilot license training flight near Gliwice when the crew experienced engine issues. At approximately 9:52 a.m., the crew noticed unstable tachometer readings on the right engine. The instructor initially decided to return to the EPGL airport to land. During the approach, the engine readings stabilized, leading the instructor to abort the landing attempt and continue the flight pattern to complete training tasks.
However, during the subsequent climb at 9:57 a.m., the right engine RPM became unstable again. Simultaneously, the crew observed the right fuel tank gauge dropping to zero. The instructor then declared an emergency and requested an immediate landing. The crew informed the AFIS officer of the need for an urgent return, and the aircraft landed at 10:06 a.m. on runway 08R. During the final approach, the right engine was kept at idle in accordance with the aircraft's flight manual procedures. The landing was completed without further incident.
The investigation
The PKBWL investigation examined the engine components and flight data. Post-flight inspections revealed that the exhaust valve of the second cylinder in the right engine had burned out. Additionally, the investigation identified a malfunction in the right fuel tank level sensor, which had provided erroneous zero-fuel readings; this sensor failure was determined to be unrelated to the engine malfunction, as the tank was confirmed to be fueled during the flight.
Findings
- The unstable engine operation was caused by pressure fluctuations in cylinder number 2 following the burnout of the exhaust valve.
- The valve burnout was likely caused by excessive exhaust gas temperatures (EGT) leading to oxidation of the valve material.
- The absence of an EGT monitoring sensor prevented the crew from detecting and managing the thermal performance of the engine effectively.
- The instructor's decision to abort the initial approach and continue flying without identifying the root cause of the malfunction was noted as being contrary to good practice.
- The aircraft was using 98-octane automotive petrol, which is regularly used by the operator.