What happened
On June 20, 2005, at 08:30 h, an Air Tractor AT-401, registration EC-JAU, was preparing to perform agricultural spraying operations near Isla Mayor, Seville. After loading the aircraft with spray material, the pilot began the takeoff roll on an unpaved 630-meter runway. Approximately 200 meters before the end of the runway, the tail lifted, leading the pilot to believe sufficient runway remained for takeoff.
However, the aircraft began to descend to the right, and the right main gear struck the edge of the runway. In an attempt to manage the situation, the pilot performed a partial emergency discharge of the spray load, which briefly lifted the aircraft and allowed it to clear a nearby water canal. The pilot then executed a full discharge, but the aircraft subsequently struck the ground and slid along the terrain until it came to a complete stop. During the impact, the engine and propeller detached from the airframe and were thrown approximately ten meters forward. The pilot sustained a neck injury and contusions to the shoulders.
The investigation
The CIAIAC examined the aircraft's mechanical condition, the environmental factors, and the pilot's operational procedures. An inspection of the Pratt & Whitney R-1340-AN1 engine was conducted to determine if a power loss had occurred. While investigators found dirty air filters and some carbon buildup on the left magneto breaker, they concluded that these issues were not significant enough to cause a meaningful loss of power. The engine was found to be functioning within normal parameters prior to the impact.
Investigators also analyzed the takeoff performance under the prevailing conditions. The aircraft was operating at a high weight of approximately 7,433 lb. The investigation considered the effects of high temperature, high humidity, the unpaved runway surface, and a light tailwind, all of which contributed to an increased takeoff distance.
Findings
- The primary cause of the accident was the use of an incorrect flap configuration; the pilot used a full-flap setting (26°), which increased parasitic drag and prevented the aircraft from reaching the necessary takeoff speed.
- The takeoff distance was critically extended due to a combination of high density altitude, high humidity, the unpaved runway surface, the heavy aircraft weight, and a light tailwind.
- The pilot's emergency procedure was improper, as the flight manual does not recognize a partial discharge procedure, and a full discharge would have been necessary to reduce induced drag and weight.
- The actual engine power was slightly lower than nominal due to environmental conditions and suboptimal filter/magneto cleanliness, though not significantly enough to be the primary cause.