What happened
On December 10, 2005, at approximately 17:05 UTC, a Weedhopper ultralight, registration 30-AG, was conducting a flight test at a private airstrip in Atouguableia, Peniche. The pilot had recently transported the aircraft to the site in kit form to perform a series of significant structural and control modifications.
Following several aborted takeoff runs intended to test the aircraft's ground handling, the pilot attempted a full takeoff. Shortly after lifting off, the aircraft reached an altitude of approximately 15 meters before entering a sharp, uncontrolled right-hand turn. The aircraft subsequently spiraled toward the ground and struck the edge of the runway, resulting in the death of the pilot and the total destruction of the aircraft.
The investigation
The GPIAAF investigation focused on the extensive unauthorized modifications made to the aircraft's airframe and control systems. The pilot, an experienced hang glider pilot, had attempted to modify the two-axis Weedhopper to behave more like a three-axis aircraft or a weight-shift control (hang glider) aircraft, to which he was accustomed.
Investigators examined the aircraft's center of gravity and aerodynamic stability. They found that the pilot had installed an electric bicycle behind the pilot's seat, which shifted the center of gravity rearward. To compensate, the pilot moved the engine cradle 24 cm forward along the longitudinal axis. Additionally, the investigation looked into the new ailerons added to the wing surfaces and the reconfiguration of the rudder controls.
Findings
- The pilot's flight medical certification had expired in 1995.
- The aircraft was not registered in the Portuguese National Aeronautical Registry (RAN); it remained under its French registration, 30-AG.
- The aircraft had undergone several uncertified structural and control modifications, including the addition of ailerons that increased the wing area and chord.
- The increase in wing chord shifted the aerodynamic center rearward, creating a nose-down tendency that was not corrected.
- The pilot had reconfigured the control inputs to mimic hang glider mechanics, which involved crossing the rudder pedals—a maneuver that is counter-intuitive and likely caused cognitive conflict during the emergency.
- The rudder control cables had been repaired using risky Nicopress sleeves, which were found broken near the joints.
- The primary cause of the accident was the pilot's loss of control of the aircraft, contributed by the uncertified and unstudied modifications to the flight controls and airframe structure.