What happened
On May 3, 2012, a Cessna 152, registration PR-KNB, departed from Maricá Aerodrome, RJ, for a navigation training flight toward Campos dos Goitacazes, RJ. The flight was operated by QNE Escola de Aviação Civil with an instructor and a student pilot on board.
Approximately five minutes after takeoff, the instructor noticed intense vibrations, followed by a drop in RPM and oil pressure, which culminated in a sudden engine shutdown. After attempting to restart the engine without success, the instructor performed an emergency landing on the sand at Praia da Barra de Maricá. The aircraft traveled approximately 120 meters along the shoreline before coming to a stop near the water. The aircraft sustained light damage to the horizontal stabilizer, and both occupants were uninjured.
The investigation
The investigation focused on the Lycoming O-235-L2C engine, which had undergone an overhaul in July 2011. The engine was sent to the Department of Aerospace Science and Technology (DCTA) for detailed analysis. Investigators discovered that the crankshaft had sheared at the connecting rod journal for cylinder number 3.
Evidence indicated that this specific journal had undergone overheating, reaching temperatures within the material's plastic tension range. While oil residue was present in other bearings and moving parts—suggesting the overall lubrication system was functional—the failure was attributed to a lack of or reduced lubrication specifically at the number 3 journal. Investigators also noted that the crankshaft oil delivery tube was correctly positioned and that the dimensions of the remaining journals and bearings were within manufacturer specifications. Due to the extent of the damage at the shear point, the precise mechanism that initially triggered the lubrication restriction could not be determined.