What happened
On May 15, 2020, a Piper PA-25-235 performing agricultural spraying operations departed from an airstrip in Luiz Alves, Santa Catarina, for a local mission. Approximately twenty minutes into the flight, while the pilot was climbing at roughly 750 feet above the application area, an explosion occurred within the engine, followed by intense vibration. The failure caused engine oil to spray across the aircraft's windshield, severely obscuring the pilot's vision.
In response to the sudden loss of power and loss of visibility, the pilot initiated a left level turn to locate a suitable landing site. After jettisoning the agricultural chemicals, the pilot performed a forced landing into a banana plantation in Ilhota, Santa Catarina. The aircraft sustained substantial damage, but the pilot emerged uninjured.
The investigation
CENIPA investigators examined the Textron Lycoming O-540-B2C5 engine and recovered several components, including a dynamic counterweight, bushing, retaining ring, and washer. Technical analysis conducted by the Department of Aerospace Science and Technology (DCTA) revealed that the engine failure was caused by the detachment of a dynamic counterweight from its housing.
Physical examination of the recovered parts showed evidence of fractures due to overload, with no signs of corrosion or fatigue. The investigation focused on the internal retaining ring, which had been replaced during the engine's last overhaul in July 2019. Investigators determined that the centrifugal force of the operating engine likely caused the counterweight to exit its seat after the retaining mechanism failed, leading it to collide with internal engine components, such as the camshaft, and eventually breach the engine block.