What happened
On May 21, 2005, at approximately 10:15 UTC, a Zephyr 2000 ultralight aircraft, registration CS-UNI, disintegrated in mid-air while flying over the Vinhó area in the Arganil municipality. The aircraft was performing a visual flight rules (VFR) flight from Alqueidão to Seia.
During the flight, the pilot exhibited erratic behavior, including significant variations in altitude and heading. Radar tracking showed the aircraft flying at altitudes that were inconsistent with safety requirements for the mountainous terrain. At one point, the aircraft appeared to be flying in circles. Witnesses on the ground reported hearing a loud boom and seeing the aircraft break apart into pieces. The debris field covered an area of more than two hectares. The fuselage and engine plummeted into a field near a primary school, where a post-impact fire consumed the wreckage. Both the pilot and the passenger sustained fatal injuries and died instantly.
The investigation
The GPIAAF investigation relied on radar records, communications with the Flight Information Service (FIS) in Lisbon, and eyewitness accounts. The investigation noted that while the aircraft was legally registered and the pilot held valid licenses, maintenance documentation for the aircraft and engine could not be located.
Investigators examined the wreckage and found fracture patterns on the wing and horizontal stabilizer. These fractures were consistent with structural failure caused by excessive aerodynamic loads. The investigation also analyzed meteorological data, which showed a continuous cloud layer across the flight path, with cloud bases at times lower than the surrounding mountain peaks.
Findings
- The pilot attempted to maintain VFR flight despite weather conditions that did not allow for the required cloud clearances or terrain separation.
- The aircraft's flight path was irregular, involving uncoordinated changes in direction and altitude.
- The pilot likely executed an aggressive recovery maneuver at high speed while flying through unstable air and attempting to descend below the cloud layer.
- This maneuver exceeded the structural load limits of the Zephyr 2000, leading to the structural failure of the wings and tail assembly.