B1/2004L Ultralight aircraft accident in Hollola on 16 February 2004

On February 16th 2004 at 15.18 local time (LT), an ultralight aircraft Dynamic WT-9 crashed during a cross-country flight in Hollola, near Lahti. The pilot of the aircraft fell through the canopy as the aircraft was inverted, and was killed. The passenger remained on his seat as the aircraft continued its dive another 800 meters before it impacted to the ground. The passenger was seriously injured. On February 17th 2004, the Accident Investigation Board Finland, in the decision B1/2004L, decided to conduct an investigation into the accident. Investigator Tapani Vänttinen was nominated as the Chairman of the Investigation Commission and Aircraft Accident Investigator Hannu Melaranta as a member of the Commission.

The aircraft had departed from Hyvinkää airport to Vesivehmaa airport earlier that afternoon. After a short stop in Vesivehmaa, the aircraft was supposed to return to Hyvinkää. Departure from Vesivehmaa took place at 15.10 LT. The aircraft headed south, and at the distance of 8 KM, it entered into uncontrolled steep pitch-up attitude, turned inverted, and continued in an inverted dive until the point of impact.

The pilot had relatively short experience and his type training to this particular aircraft type was insufficient. The aircraft possessed longitudinal controllability problems that were noticed during the check-flight programme, which was conducted when the aircraft was imported into the country. Different versions of the flight manual and the weight and balance certificate presented contradictory values for the center of gravity limits of the aircraft. The weight of the aircraft and it’s center of gravity were out of limits during the time of the accident. No technical fault contributing the accident was found during the investigation.

The probable cause of the accident was overweight and center of gravity that was well beyond the aft limit. As a result, the aircraft became unstable. When the horizontal stabilizer was suddenly pulled back, either by a gust or by the pilot unintentionally, the aircraft entered rapidly in a steep nose-up attitude and further inverted. The pilot had not fastened his seatbelts, or had unfastened them at some point, so he fell through the canopy. One reason for the pilot’s unfastened seatbelts could be that they were deliberately unfastened in order to reach for the luggage compartment behind the seats. As a result of this kind of movement, the center of gravity would move even further backwards, making the aircraft more unstable. The horizontal movement of the aircraft had been so rapid, that the pilot had no chance to make corrective action. It is also possible, that as the airspeed decreased, the possible corrective action had no longer effect on the movement of the aircraft.

The Investigation Commission made three safety recommendations as a result of the investigation. The Finnish Aeronautical Association is recommended to emphasize the importance of the student’s ability to fully understand the contents of their training and that the training is complemented with practical examples and learning is confirmed by examinations. This should be achieved by stressing the matter during teacher’s basic and supplementary training. The Finnish Flight Safety Authority (FSA) is recommended to draw their attention to the performance and handling qualities of various ultra-light aircraft types and to define, if necessary, the requirements set for type training. Further, the FSA is recommended to consider bringing the ultra-light pilot’s licence requirements up to date and in line with the current aircraft types’ requirements and field of use.

B1/2004L Report (pdf, 0.78 Mt)