Background
In the months preceding the incident, wild boars had repeatedly damaged the grass runways and taxiways at Fricktal Schupfart airfield (LSZI). To deter the animals, an electric flash device mounted on a pole (referred to as a wild boar protection device) was installed. The device was moved to various locations over time, but its positions and the dates of relocation were not documented. The identity of the person(s) who installed and moved the device could not be determined.
Several days before the incident, another aircraft of the same type (Christen A I Husky) had collided with the same device at a different location. In that occurrence, the wing strut only grazed the device, resulting in no damage. The pilot of that aircraft subsequently spoke with the airfield groundskeeper, but the airfield manager was not contacted.
Incident
On Saturday, 8 September 2018, the airfield had assigned separate tow pilots for the morning and afternoon periods. There was no handover briefing between the two pilots.
After refueling and conducting a preflight check, the pilot boarded the tailwheel aircraft, registered as HB-KCI, which was parked pointing toward runway 25. The pilot started the engine and intended to taxi toward the holding position of runway 07. Approximately 50 meters into the taxi, a dull thud was heard from the wing area, and the pilot saw an object flying through the air. The pilot immediately stopped the aircraft and shut down the engine.
Findings
According to Swiss national guidelines for visual aids on unpaved runways and taxiways (AD I-002), markings or flags with a maximum height of 35 cm are permitted along grass taxiways and runways. If an object is located within the taxiway, minimum separation distances between the object and the taxiway must be observed.
The wild boar protection device had been moved repeatedly without documenting its locations. Neither the airfield manager nor the pilot had been informed of the device's most recent position at the time the pilot taxied toward the holding position of runway 07.
The aircraft had been parked directly aligned with the device after refueling. While taxiing to the point of collision, it was nearly impossible to see the obstacle from the cockpit.
Analysis
The investigation determined that the obstacle was placed within the taxiway area without adherence to national guidelines for obstacle-free zones. The lack of documentation and communication regarding the device's location contributed to the collision. However, the guidelines clearly specify the required clearances, and therefore the event was not attributed to a systemic deficiency.
The aircraft sustained minor damage: the propeller was damaged, and the left wing underside had a small scratch. The wild boar protection device was also damaged.