What happened
On January 5, 2025, a ground collision occurred at Visby Airport involving two aircraft operated by the Voluntary Air Corps (FFK) during a formation flight training session. The aircraft involved were a Daher TB 9, registration SE-KBL, and a Daher TB 10, registration SE-KBF.
Prior to the incident, the two aircraft were positioned on an extension of the apron, both angled toward the left. The ground was covered in snow and ice, though the pilots had assessed the surface friction as good. Following engine start, the rear aircraft, SE-KBF, began moving forward unexpectedly. The pilot attempted to use the wheel brakes to stop the movement, but the aircraft continued forward until its propeller struck the left wing of SE-KBL, resulting in structural damage to both aircraft. No injuries were reported.
The investigation
The Swedish Accident Investigation Authority (SHK) examined the braking systems, engine performance, and the positioning of the aircraft. Investigators found no technical defects in the braking system of SE-KBF; the brakes functioned normally when applied. While the pilot reported that the brakes provided insufficient stopping power, the investigation suggested that the primary issue was the high level of thrust generated during the engine start sequence.
Analysis of the ground tracks and witness accounts indicated that the engine power was higher than the standard 1000–1200 RPM range typically used during start-up. This increased thrust, combined with reduced ground friction due to the icy conditions, caused the aircraft to slide. Furthermore, the investigation determined that the aircraft were parked too close to one another, leaving no margin for error if unintended movement occurred.
Findings
- The primary cause of the collision was that high engine power during the start sequence exceeded the available ground friction.
- The aircraft were positioned at an angle and distance that did not provide sufficient obstacle clearance.
- The risks associated with the aircraft positioning and the prevailing slippery surface conditions had not been fully addressed during flight preparations.
Safety action
Following the incident, both the Gotland Flying Club and the Voluntary Air Corps have implemented measures to mitigate collision risks during engine starts. Because these corrective actions have already been initiated, the SHK did not issue formal safety recommendations.