What happened
On March 18, 2020, a PA-25-260 aircraft, registration PT-LZC, was performing agricultural spraying operations in Garuva, Santa Catarina. During the final pass of a fungicide application, the pilot heard a loud noise followed by a sudden loss of engine power. As the pilot attempted to return to the landing area, smoke and fire became visible in the engine compartment.
In response to the developing fire, the pilot shut off the engine and executed a forced landing into a banana plantation. The aircraft sustained substantial damage to the powerplant, landing gear, wings, and control surfaces. The pilot escaped the wreckage without injury.
The investigation
CENIPA investigators examined the wreckage and the Textron Lycoming O-540-G1A5 engine. The investigation revealed that cylinder number 4 had detached from the engine block during flight. Physical evidence showed that the remaining stud bolts had failed due to overload following the initial failure of a primary bolt.
Analysis of the remaining stud bolt indicated signs of fatigue. Investigators considered several hypotheses, including the possibility that improper torque was applied to the cylinder fixing nuts during a previous engine overhaul or unrecorded maintenance service. While the aircraft's logbooks showed inconsistencies in total hours computation, investigators determined this was not a direct cause of the accident, though it highlighted flaws in maintenance supervision.
Findings
- The engine failure was caused by the detachment of cylinder number 4 due to the failure of the engine's stud bolts.
- The failure of the initial bolt was likely due to a fatigue process.
- The subsequent failure of the remaining bolts was caused by the resulting mechanical overload.
- Aircraft maintenance was identified as a contributing factor, specifically the possibility that improper torque application during engine assembly led to the fatigue and eventual rupture of the bolts.