What happened
On August 13, 2009, an Air Tractor AT-502B, registration EC-IVX, was operating at the Ocaña Aerodrome in Toledo, Spain, performing aerial application services. While taxiing toward runway heading 11, the pilot encountered several gliders positioned near the runway threshold, preventing the use of the first 3 and 300 meters of the runway. To utilize the full runway length for takeoff, the pilot steered the aircraft to the right, onto the runway shoulder, intending to taxi along the verge to reach the far end.
During this maneuver, the aircraft began a progressive leftward turn. As the aircraft moved along the shoulder, the turn became increasingly sharp, eventually resulting in a 180-degree rotation. During this sequence, the tail section of the aircraft suffered a structural failure. The aircraft eventually came to a stop on the right side of the runway, aligned with the intended takeoff direction.
The investigation
The investigation focused on the structural failure of the tail assembly and the sequence of the taxi maneuver. Investigators examined the wreckage and found that the rear fuselage had partially detached due to the breakage of the right-side lower structural tube and the surrounding skin panels. The tailwheel assembly had also detached from its spring, and the tail strut was positioned nearly parallel to the ground, causing the fuselage to rest directly on the pavement.
Analysis of the ground tracks revealed that the aircraft initially moved away from the runway before beginning a gradual leftward turn. As the turn intensified, the aircraft began to skid. The investigation determined that the right main wheel impacted the pavement with enough force to cause multiple bounces. When the tailwheel finally made contact with the runway, it was subjected to a massive lateral load.
Findings
- The primary cause of the accident was the uncommanded leftward turn initiated during taxi, which the pilot did not perceive, leading to a loss of directional control.
- The structural failure of the tail assembly was caused by a static overload, specifically a heavy lateral load transmitted through the tailwheel spring during the skid.
- The tailwheel locking mechanism was likely not engaged; because the aircraft was turning, the locking pin and the housing hole were not aligned, preventing the wheel from being centered and locked.
- Environmental factors, including a light southeasterly wind and the engine's torque effect, contributed to the increasing leftward rotation.
- The pilot's limited visibility of the immediate area adjacent to the aircraft and the belief that the tailwheel was locked likely prevented timely corrective action.