What happened
On July 17, 2004, an Aisa I-11B, registration EC-BUY, was performing local flight operations at the San Luis Aerodrome in Menorca. The pilot had previously completed several flight segments that day. During the final takeoff attempt, the pilot noted a lack of rudder response while attempting to align the aircraft with runway 02, necessitating a manual repositioning of the aircraft after stopping the engine.
As the aircraft accelerated and climbed to an altitude of approximately 10 meters, it began a sharp left turn. The aircraft entered a series of unstable oscillations, characterized by sudden pitching and rolling movements. Despite the pilot's attempts to recover control by pushing the control column forward to gain speed, the aircraft continued to wobble and eventually struck the ground with high vertical velocity and low horizontal speed. The impact caused significant damage to the fuselage, wings, and engine.
The investigation
The CIAIAC examined the aircraft's control systems, the wreckage distribution, and the condition of the safety equipment. Investigators found that the flight control surfaces, including the elevators and rudder, were functional and connected to the cockpit controls. A single broken cable was found in the trim tab mechanism, but it was determined that this was caused by static overload during the impact rather than a pre-existing failure.
Regarding occupant protection, the investigation revealed that the two-point seatbelts were severely degraded. Although they appeared intact to a visual inspection, the synthetic fibers disintegrated upon touch. During the impact, both seatbelts failed, causing the pilot and the passenger to be thrown forward against the aircraft structure. The pilot sustained multiple fractures and deep lacerations, while the passenger suffered facial cuts and contusions.
Findings
- The primary cause of the accident was the development of Dutch roll instability during a left turn at low altitude and low airspeed, triggered by the wing dihedral effect.
- The pilot's attempt to recover by pitching the nose down was unsuccessful due to the insufficient altitude available.
- The degraded condition of the seatbelts contributed to the severity of the pilot's injuries by failing to restrain the occupants during the impact.
Safety action
- A recommendation was issued to the DGAC to implement an inspection program for the historical aircraft fleet in Spain to assess the condition of installed seatbelts and determine if service life limitations are necessary.