What happened
On February 16, 2004, at approximately 15:18 local time, a Dynamic WT-9 ultralight aircraft, owned by Mäntsälän Ilmailukerho, crashed in the Kallio village area of Hollola. The aircraft had departed from Vesivehmaa airport heading south following a stop from Hyvinkää.
Approximately 8 kilometers from Vesivehmaa, the aircraft entered an uncontrolled flight state characterized by a sudden, steep pitch-up attitude that transitioned into an inverted position. The aircraft then entered a steep dive with the engine stopped, gliding for another 800 meters before impacting a field. During the sequence, the pilot fell through the aircraft's canopy and was killed. A passenger sustained serious injuries.
The investigation
The investigation examined the aircraft's weight and balance, the pilot's training, and the aircraft's technical condition. Investigators found that the aircraft was 18% overweight, exceeding the maximum takeoff weight of 450 kg by 85 kg. Additionally, the center of gravity was 36 mm beyond the aft limit.
Discrepancies were noted in the flight manual versions and the weight and balance certificate regarding center of gravity limits. The investigation also looked into the pilot's experience and the aircraft's longitudinal stability, noting that previous check-flights during importation had already identified stability issues. No technical mechanical failure contributing to the accident was identified.
Findings
- The aircraft was significantly overweight and the center of gravity was too far aft, rendering the aircraft longitudinally unstable.
- The aircraft entered an uncontrolled pitch-up and inverted state due to a wind gust or an unintentional movement of the elevator, exacerbated by the unstable weight distribution.
- The pilot's seatbelts were unfastened; it is suspected the pilot may have unfastened them to reach the rear luggage compartment, an action that would have shifted the center of gravity even further aft.
- The pilot had relatively limited flight experience and insufficient type training for this specific aircraft model.
- No weight and balance calculations had been performed prior to the flight.