What happened
On October 11, 2013, a Cessna 152, registration PT-FCA, was conducting a local instructional flight near Bacacheri, Brazil, when the engine experienced a significant power loss. The flight, operated by Aerocon Escola de Aviação Civil, carried an instructor and a student.
Ten minutes into the flight, the instructor noticed that despite applying full power, the tachometer indicated only 2200 RPM while the aircraft remained in level flight. This was immediately followed by a sudden drop in power, intense engine vibrations, and white smoke emitting from the engine air intake. The propeller subsequently locked. After three unsuccessful attempts to restart the engine, the instructor configured the aircraft for a glide and performed an emergency landing on the BR-116 highway near Quatro Barras, Paraná. Both occupants escaped the incident uninjured, though the aircraft sustained substantial damage to the engine.
The investigation
CENIPA investigators conducted a detailed inspection of the Lycoming O-235-L2C engine at a maintenance facility in Bacacheri. The external inspection revealed a crack in the upper engine block caused by the impact of an internal rotating component.
Upon disassembling the engine, investigators found a significant amount of metal debris (swarf) within the oil filter and the crankcase. The investigation established that the connecting rod journal for cylinder number 2 had operated without proper lubrication, leading to overheating and the observed crack. The failure sequence was traced to the loss of torque on one of the nuts securing the cylinder number 2 connecting rod cap. This allowed the bolt to shift, causing it to strike internal engine components, which stripped the threads and eventually led to the bolt snapping due to overload. This mechanical failure caused the connecting rod to become detached from the cap, remaining attached only to the piston.