What happened
On March 5, 2013, a Cessna 152 was performing a takeoff from the Bielsko-Biała Aleksandrowice (EPBA) aerodrome. Shortly after liftoff and during the transition to the climb phase, the flight crew, consisting of an instructor and a student pilot, experienced a significant loss of engine power accompanied by intense engine vibrations.
Upon evaluating the situation, the instructor determined that attempting an immediate aborted takeoff and landing straight ahead would not allow the aircraft to stop safely within the airport boundaries. Consequently, the decision was made to continue the flight. The crew executed a small circuit and successfully landed the aircraft back at the aerodrome. Following the landing, a ground engine test and compression check were performed. While cylinders 1, 2, and 4 showed normal pressure, cylinder 3 recorded zero compression. Subsequent disassembly of the cylinder revealed that the exhaust valve was stuck in the open position.
The investigation
The investigation examined the recent maintenance history of the engine. Prior to the incident, maintenance tasks were performed at two different maintenance organizations (referred to as A and B). Following 100-hour and 400-hour inspections, and in accordance with Service Bulletin SB388C, clearances between the valve stems and guides were checked. During these inspections, excessive clearances were noted in cylinders 3 and 4.
Repairs to these cylinders were carried out by organization B, after which they were reinstalled on the engine by organization A. Following the reinstallation, the engine underwent testing and showed correct parameters. The engine had operated for approximately 50 minutes following this maintenance package.
Upon further inspection of the removed cylinder 3 by organization B, investigators confirmed that the exhaust valve was stuck open. While the diameters of the valve guide and stem were within correct limits, visible scoring/seizure was found on the lower part of the guide surface. This seizure was caused by a fragment of carbon deposit (soot) that had become lodged between the valve stem and the guide during engine operation.
Findings
- The primary cause of the engine power loss was the entry of a carbon deposit fragment between the valve stem and the guide of the cylinder 3 exhaust valve, which caused the valve to seize in the open position.
- The investigation could not determine the exact timing or the specific cause of how the carbon fragment entered the space between the stem and the guide.