What happened
On June 18, 2015, a Piper PA36-375, registration CS-AUC, was performing aerial spraying services at the Biscainho Brandão agricultural airstrip near Coruche, Portugal. The aircraft had been prepared with fuel and phytosanitary products for the mission.
While waiting for ground crews to finish their procedures, the pilot observed vegetation moving in the wind, suggesting a preference for using runway 1s. Deciding that the wind intensity was not a hindrance, the pilot aligned the aircraft on runway 31, which was closer to the loading position. The aircraft began its take-off roll with the first notch of flaps selected. However, the aircraft failed to reach the required take-off airspeed of 80 mph.
During the final phase of the take-off run, the pilot selected full flaps, but the aircraft was unable to overcome obstacles and began to sink. The aircraft struck a cork tree with a pronounced left wing-down attitude, followed by a second collision with another tree, and finally came to rest at the base of a third tree. The impact was severe enough to separate the engine and propeller from the primary structure. The pilot sustained serious injuries, including head trauma and chest injuries, and was evacuated by helicopter to a hospital in Lisbon.
The investigation
The GPIAAF investigation examined the aircraft's mechanical state, the airfield conditions, and the operational procedures. Investigators found that the aircraft was not equipped with a flight data recorder. The investigation also noted that the aircraft's emergency cargo release system was inoperative, and the pilot had attempted to compensate by selecting full flaps, which contributed to the loss of control.
Regarding the airfield, the investigation established that the agricultural airstrip did not meet regulatory requirements for wind direction indicators or firefighting and rescue services. The runway, which had a declared length of 500 meters, featured a positive slope of approximately 1.7% in the first 400 meters and was bordered by large cork trees reaching heights of about 10 meters.
Findings
- The aircraft experienced an asymmetric aerodynamic stall due to low aerodynamic control speed, which caused the left wing to drop.
- An unsafe precondition existed because the emergency cargo release system was inoperative, and the pilot had used an improvised method to inhibit the valve.
- The pilot's decision to continue the take-off despite not reaching the required airspeed, combined with the selection of full flaps, led to the loss of control.
- Environmental and operational factors, including a tailwind, the runway slope, and the probable heavy loading of the aircraft, contributed to the accident.
- Maintenance practices were identified as deficient, specifically regarding the lack of traceability for certain anomalies and repairs.