What happened
On July 12, 2020, an Air Tractor 3/01, registration HK4968, was conducting agricultural spraying operations near Apartadó, Colombia. After completing a mission over the Monterrey 1 farm, the pilot was returning to the Los Almendros base at an altitude of approximately 700 feet.
During the return flight, the pilot experienced a loud noise and severe vibrations that were so intense they obscured the cockpit instruments. The pilot observed smoke and oil escaping from the engine before the powerplant failed completely. Unable to reach the nearby Indira airstrip, the pilot executed an emergency landing on a roadway near the village of Currulao.
While the pilot managed a controlled touchdown on the road, the aircraft collided with a vehicle traveling in the opposite direction during the deceleration phase. Both the aircraft and the vehicle veered off the road. The pilot and the driver of the vehicle were both uninjured.
The investigation
The GRIAA investigation focused on the mechanical failure of the Pratt & Whitney engine and the operator's maintenance practices. Investigators examined the engine components and found that the connecting rod had fractured due to material fatigue.
Further scrutiny of the operator's records revealed significant discrepancies in maintenance tracking. The investigation found that the operator's maintenance manual incorrectly specified engine overhauls at 1,200 hours, whereas the manufacturer's requirements for agricultural aircraft mandate service between 600 and 1,000 hours. Additionally, the operator was using an inaccurate method for calculating engine flight time, recording only the interval between takeoff and landing rather than the time from engine start to engine shutdown. This practice likely resulted in engines operating well beyond their safe service limits.