What happened
On December 25, 2019, a Piper PA-36-375, registration PR-AEC, was performing an agricultural spraying mission over a soybean field near Itambé, Paraná. The aircraft had departed from the Ivaí Aeroagrícola airfield for a local flight. During the operation, the pilot experienced a sudden engine failure accompanied by an explosion-like sound, smoke in the cabin, and oil spraying onto the windshield. Following the engine stoppage, the pilot executed a forced landing into the crop. The pilot was uninjured, but the aircraft sustained substantial damage.
The investigation
CENIPA investigators examined the Lycoming IO-720-D1CD engine and the aircraft's maintenance history. The investigation focused on the mechanical failure that led to the sudden loss of power. Technical analysis was conducted by the Department of Aerospace Science and Technology (DCTA) and the Institute of Aeronautics and Space (IAE). Investigators also reviewed the aircraft's records, noting that while the pilot was properly licensed and the aircraft held a valid Special Flight Authorization (AEV) for ethanol use, the aircraft's logbooks for the airframe, engine, and propeller were not up to date regarding monthly hour entries.
Findings
Technical analysis of the engine revealed that the failure was triggered by the fatigue of a crankshaft bushing and its housing. The fatigue-induced breakage of the bushing allowed the dynamic counterweight to detach due to centrifugal force. This detachment caused the counterweight to strike the engine block, perforating it and damaging cylinders 5 and 6. Additionally, the impact caused the rupture of the camshaft. Metal shavings and fragments were discovered in the primary oil filter and the engine crankcase, confirming the internal structural failure.