What happened
On April 7, 2018, a Robin DR 40 and/80 R, registration HB-KAW, was prepared for glider towing operations at Sion Aerodrome (LSGS). The pilot, having just completed a separate instructional flight, intended to perform several glider tugging duties. Because the aircraft had been in use throughout the day, the pilot approached the aircraft from the rear and boarded without performing a formal pre-flight inspection, relying instead on the assumption that the previous user had left the aircraft in a safe condition.
During the taxi phase toward the grass takeoff area, the pilot executed a 180-degree left turn. During this maneuver, the propeller struck the tow bar, which had been left positioned in line with the nose wheel. The pilot heard a sudden impact and immediately shut down the engine. A ground crew member inspected the aircraft and informed the pilot that there was a small mark on the propeller. Believing the damage to be negligible, the pilot remained in the cockpit, performed engine and control checks, and proceeded to take off at 17:53. The towing flight was completed without further incident, but upon returning to the ground, the pilot discovered the extent of the damage to the metal propeller and the nose wheel tow bar.
The investigation
The investigation focused on the circumstances leading to the contact between the propeller and the tow bar. Investigators examined the pilot's actions regarding the pre-flight inspection and the subsequent assessment of the propeller damage. The investigation confirmed that the propeller was heavily damaged and the tow bar was also impacted. Following the event, the engine and propeller were removed for inspection, and the propeller was found to be beyond repairable limits.
Findings
- The pilot omitted a pre-flight inspection, which prevented the detection of the tow bar's position relative to the nose wheel.
- An unqualified ground crew member provided an initial assessment of the propeller damage, which was misleading.
- The pilot failed to personally verify the extent of the damage, assuming the impact was minor, and proceeded with a scheduled flight despite the unidentified structural risk.