What happened
On August 10, 2011, a Pilatus PC6 H2B2, registered F-BTCG, was conducting parachute deployment operations at the Besançon-Thise aerodrome. The aircraft was operating from this location temporarily because its usual base, Besançon-la-Vèze, was undergoing runway resurfacing work.
While taxiing on an unpaved taxiway toward the threshold of runway 06 left for a second rotation, the pilot was observing a tractor performing mowing operations on the right side of the path. During this period of observation, the pilot lost sight of the yellow taxiway edge markers near the runway intersection. As the pilot turned left toward the runway, the aircraft drifted off the taxiway and the right wing struck a sign marking the boundary of the aerodrome's restricted area. The impact caused significant damage to the underside of the wing and the aileron.
The investigation
The investigation focused on the positioning of the sign and the pilot's visibility during the taxi maneuver. The sign, which stood 2.35 meters tall, was located 22.2 meters from the center of the taxiway. The taxiway has a half-width of 10 meters. Investigators confirmed that the placement of the sign met all applicable regulatory requirements for the aerodrome.
Measurements of the aircraft's wing showed that the leading and trailing edges were at a height of 2.31 meters. The pilot, who had over 20 years of experience but was unfamiliar with this specific aerodrome, noted that he had not seen the sign. The investigation also considered the aircraft's configuration, noting that the visibility inherent to a conventional landing gear (taildragger) aircraft can make detecting low-profile markers more difficult during taxi.
Findings
- The pilot's attention was diverted by the mowing activity occurring alongside the taxiway, leading to a failure to monitor the taxiway edge markers.
- The aircraft veered off the taxiway due to this loss of situational awareness.
- The visibility of the taxiway markers and the sign was likely reduced by the flight attitude of the Pilatus PC6 H2B2 during taxi.
Safety action
- The local DSAC delegation requested that the aerodrome operator relocate the sign.