What happened
On June 29, 2015, at approximately 19:40 UTC, an Air Tractor AT-402A, registration PT-MSB, was performing agricultural spraying operations at Fazenda Planta in Sapezal, Mato Grosso. The aircraft was engaged in its ninth takeoff of the day, applying pesticides to a corn plantation.
Shortly after lifting off from the dirt runway, the aircraft suffered a sudden loss of engine power. Unable to maintain flight, the pilot performed an emergency landing in a cornfield located just ahead of the takeoff area. The aircraft traveled approximately 25 meters before coming to a complete stop. The impact resulted in substantial damage to the aircraft, though the pilot emerged uninjured.
The investigation
CENIPA investigators examined the Pratt & Whitney PT6A-11AG engine and its components. Post-accident testing of the fuel pump, Fuel Control Unit (FCU), and propeller governor was conducted by specialized maintenance organizations with oversight from investigators and manufacturer representatives.
While the engine's air lines and oil filter showed no abnormalities, inspections of the propeller governor revealed that the relief valve was stuck. Additionally, investigators found that the Ng stop had been adjusted in the field, as evidenced by a missing locknut. The investigation also noted that the differential pressure (ΔP) signal from the governor to the FCU was significantly below the manufacturer's required specification.