What happened
On September 26, 2018, at Grenchen Airport (LSZG), a pilot was taxiing a Piper J3C-65/L-4, registration HB-OUS, following a completed pleasure flight. After refueling at a fuel pump, the pilot began taxiing toward Hangar 83 with the engine running, while monitoring the airport traffic control frequency.
During the taxi, the pilot observed a twin-engine Beechcraft BE18, registration N223CM, stationary on taxiway N with its engines running. Because the propellers of the BE18 were rotating at a low speed, the pilot decided to continue taxiing past the aircraft while maintaining elevator back pressure. As the HB-OUS crossed behind the BE18, the right wing suddenly lifted, causing the left wingtip to strike the ground. The aircraft then pitched forward and came to a rest in a nose-up position after the propeller made contact with the surface. The pilot exited the aircraft without injury.
The investigation
The investigation established that the crew of the BE18, consisting of two mechanics, were performing a magneto test on taxiway N. During this procedure, the mechanics increased the engine speed to 1,950 RPM.
Investigators found that the location used for this engine run was not designated for such testing according to the Grenchen Airport manual. Furthermore, the air traffic control service had not been notified of the intended engine run. While the mechanics were conducting the test, the sudden increase in power from the BE18 created a significant propeller blast.
Findings
- The primary cause of the incident was the propeller blast from the BE18, which exerted enough force to destabilize the taxiing Piper L-4.
- The BE18 was performing engine tests at 1,950 RPM, a high power setting for the aircraft.
- The engine run was conducted on a taxiway not authorized for such operations.
- Air traffic control was not informed of the engine testing in progress.
- The HB-OUS sustained heavy damage to its propeller, engine, engine cowling, and the leading edge of the left wing.