What happened
On February 1, 2016, at approximately 14:30 UTC, a Chincul Sacaifi PA-25-260, registration PT-OQV, was conducting an agricultural reconnaissance flight near Sete Barras, São Paulo. The flight was intended to survey a spraying area characterized by various small plots marked by flags. After roughly 25 minutes of flight, the pilot noticed power oscillations followed by a drop in oil pressure. The pilot performed an emergency landing in a rural area, which resulted in substantial damage to the aircraft. The pilot was uninjured.
The investigation
CENIPA investigators examined the Lycoming O-540-G1A5 engine and the aircraft's maintenance records. The investigation confirmed that the aircraft was airworthy, within weight and balance limits, and that all maintenance logs for the airframe, engine, and propeller were up to date. Fuel samples analyzed by the Aeronautical Propulsion Division (APA) showed no signs of contamination and met all regulatory specifications, ruling out fuel starvation.
Upon disassembly of the engine, investigators found metal fragments and shavings within the oil pan. A fracture was identified in the engine block near cylinder number 5. Detailed analysis revealed that the connecting rod bolts for cylinder number 5 had fractured due to overload. Furthermore, the investigation found evidence of overheating in the cylinder number 4 bearing and melting on the cylinder number 5 crankpin.
Findings
- Loss of torque in one of the nuts securing the connecting rod cap to the crankshaft.
- Internal lubrication failure caused by the loosening nut, which allowed oil pressure to escape directly into the oil pan.
- Mechanical failure of the cylinder number 5 connecting rod bolts due to overload.
- Substantial damage to the engine components, including melted crankpin surfaces and bearing damage.
- Undetermined maintenance and managerial supervision factors.