What happened
On September 30, 2018, a PZL-104 Wilga, registered D-ELOH, was conducting a private flight from Bad Ragaz (LSZE). Following a successful landing, the pilot taxied the taildragger aircraft toward a designated parking area located on a grassy field northwest of the main building. During this taxiing phase, the pilot failed to notice a small, green-painted aluminum box, approximately 40 cm in height, positioned in the aircraft's path.
As the aircraft approached its stopping point, the rotating propeller struck the box. The impact caused the propeller to disintegrate into multiple fragments, with some debris being thrown as far as 200 meters from the aircraft. Although the pilot immediately shut down the engine, the resulting severe imbalance caused intense vibrations throughout the airframe. These vibrations were powerful enough to force the engine cowling into the windscreen, causing the glass to shatter, and placed such stress on the engine mount attachment points at the firewall that the forward fuselage structure was deformed. There were no injuries to the pilot or the passenger, and no damage was caused to third-party property.
The investigation
The investigation was initiated after the SUST was notified of the event by an eyewitness in late November 2018. The inquiry examined the sequence of the taxiing maneuver, the visibility constraints inherent to the aircraft type, and the presence of the obstacle on the airfield. The investigation also noted that the incident was not reported immediately to the required authorities following the occurrence.
Findings
- The primary cause of the propeller failure was the collision with an unobserved obstacle on the taxiway.
- The visibility from the cockpit of a taildragger aircraft is significantly restricted during forward taxiing.
- The green color of the aluminum box contributed to it being difficult to detect against the airfield environment.
- The extreme vibrations following the propeller breakup led to secondary structural damage, including a broken windscreen and a deformed fuselage.