What happened
On May 24, 2010, an Air Tractor AT-401, registration EC-IXJ, was returning to its base at the El Reboso landing strip in Los Palacios y Villafranca, Spain, after completing rice sowing operations. As the aircraft approached the southern end of the runway, it performed a maneuver to transition from the base leg to the final approach.
During this turn, the aircraft reached an excessive bank angle, reportedly as high as 80 degrees. This maneuver caused the aircraft to enter a stall at a very low altitude, approximately 10 to 15 meters above the ground. The aircraft then rolled sharply to the right and descended toward the runway area, where two other aircraft, EC-HFJ and EC-GYX, were positioned near the runway threshold.
The right wing of EC-IXJ struck the left horizontal stabilizer of EC-HFJ, then hit the left wing of that same aircraft, and subsequently collided with a tractor. The impact caused the outer half of the right wing of EC-IXJ to be torn away. Following these collisions, the aircraft plummeted nose-down onto the runway, resulting in the engine and the left main landing gear detaching. The tail section of the aircraft also struck the nose of EC-GYX, causing damage to its exhaust manifolds, cylinder, and propeller. The aircraft finally came to rest in a ditch alongside a canal.
The investigation
The investigation focused on the flight path and the aerodynamic state of the aircraft during the turn. Investigators examined the aircraft's performance data, including stall speeds at various bank angles and weights. The investigation confirmed there were no marks on the ground prior to the collision with EC-HFJ, ruling out a loss of control due to ground contact before the initial impact.
Analysis of the aircraft's flight manual indicated that at a bank angle of 60 degrees with flaps up, the stall speed is approximately 103 mph for maximum takeoff weight. For the actual weight of the aircraft at the time of the accident (approximately 2,156 kg empty weight plus fuel), the estimated stall speed at a 60-degree bank angle was roughly 97.5 mph. Given that standard base-to-final turns are typically performed at 100 mph, the investigation concluded that the high bank angle likely pushed the stall speed above the aircraft's actual airspeed.
Findings
- The primary cause of the accident was the execution of the base-to-final turn with an excessive bank angle, which induced an aerodynamic stall.
- The pilot likely performed the turn too close to the runway, necessitating a tighter, steeper turn to align with the approach path.
- The low altitude at the time of the stall left the pilot with insufficient margin to recover the aircraft before impact.
- The pilot was wearing a flight suit, gloves, and a helmet, but the seatbelt was not tightly adjusted for maximum security, though it remained functional.
- The collision resulted in two serious injuries: the pilot of EC-IXJ and the tractor operator.