What happened
On January 5, 2021, a PA-25-235 aircraft, registration PR-TCE, was performing a local agricultural spraying flight over a sugarcane plantation near Guará, São Paulo. The aircraft took off from a landing area at Floresta Farm to apply pesticides. During the operation, the engine suffered a sudden failure, forcing the pilot to perform an emergency landing within the crop. The impact caused substantial damage to the propeller, engine, landing gear, wings, and the lower fuselage, but the pilot escaped the wreckage unharmed.
The investigation
CENIPA investigators examined the powerplant and found that the engine's electrical wiring, specifically the cables for the starter and magnetos, had deteriorated. The investigation revealed that the wiring was leaning against the exhaust pipe due to the failure of a plastic clamp used to secure the cables to the engine cradle. The heat and friction from the exhaust caused the protective insulation to degrade, eventually leading to the magneto grounding wires making contact with the exhaust.
During functional testing, investigators were able to replicate the failure by intentionally placing the magneto grounding wires against the exhaust structure, which resulted in an immediate engine shutdown. The investigation also noted that while the aircraft's maintenance logs for the airframe, engine, and propeller were outdated in their primary entries, the aircraft was within weight and balance limits and the pilot was fully qualified for the mission.
Findings
- The primary cause of the engine failure was the inadvertent grounding of the magnetos caused by deteriorated electrical wiring.
- The use of inadequate plastic clamps to secure engine electrical cabling allowed the wires to shift and contact the hot exhaust.
- Maintenance oversight contributed to the event, as the operator's management failed to ensure that appropriate metal clamps or stainless steel braiding were used for securing cables in the engine area.
Safety action
CENIPA issued recommendations to Brazil’s National Civil Aviation Agency (ANAC) to disseminate the lessons learned regarding the risks of using plastic clamps in engine compartments. Additionally, a recommendation was made to evaluate whether the aircraft manufacturer should issue technical instructions specifically guiding the proper attachment of electrical cables in the engine region of the PA-25-235.