What happened
On October 13, 2018, a Cessna 152 was conducting a training flight from Łososina Dolna airport. The crew, consisting of a flight instructor and a student pilot, intended to fly a route including stops at Krosno, Arłamów, and Rzeszów.
Approximately 11 minutes after takeoff, while descending to 2,000 feet, the aircraft experienced severe engine vibrations. The instructor took control of the aircraft and initiated a 160-degree turn back toward the airport. Shortly after the vibrations began, the engine ceased operation. Following unsuccessful attempts to restart the engine, the instructor instructed the student to shut off the fuel supply, ignition, and electrical master switch. The instructor then performed an emergency landing in an open field near Podole-Górowa. The aircraft came to a stop after a 120-meter ground roll. No injuries were sustained by the crew.
The investigation
The investigation, conducted by the operator's commission, focused on the engine's mechanical condition. Upon inspection of the engine, investigators discovered damage to the engine crankcase. The engine was subsequently disassembled by a maintenance organization for a detailed component analysis.
Investigators examined the engine's maintenance history, noting that during a 100-hour inspection, cylinder compression in the third cylinder had been recorded as below the allowable norm. However, that cylinder had been repaired and returned to service 86.7 flight hours prior to the incident. The oil pump was found to be fully functional, and no metal particles were found in the oil filter during the most recent 50-hour inspection.
Findings
Technical analysis of the disassembled engine revealed that the crankshaft had overheated, resulting in twisting and deformation along its longitudinal axis. Specific evidence included traces of a worn bearing on the connecting rod cap of the third cylinder and purple discoloration on the crankshaft, indicating extreme heat. This overheating caused the bolts securing the connecting rod cap to fail. The subsequent failure of the rod cap led to the connecting rod damaging the engine crankcase, the piston, and the third cylinder.
The investigation concluded that the primary cause was the melting of the bearing and the overheating of the third cylinder's connecting rod cap. It is believed that operating the engine with low compression in the third cylinder likely led to inadequate lubrication of the bearing, resulting in the overheating and eventual mechanical failure of the connecting rod assembly.