What aircraft was involved and where did it happen?

The accident on 2014-07-17 involved a DHC-1 Chipmunk 22 and EV-97 Eurostar Sl, registration G-ULAS and G-CIDZ, at Wycombe Air Park, Buckinghamshire, GB.

What was the probable cause of the accident?

The collision occurred when the instructor of the stationary Eurostar applied power to move forward to avoid an imminent impact, inadvertently driving the aircraft's tailplane into the propeller arc of the taxiing Chipmunk.

Mid-air collision between two aircraft at Wycombe Air Park

A collision involving a DHC-1 Chipmunk and an EV-97 Eurostar occurred at a runway holding point during taxiing operations.

What happened

On 17 July 2014, at Wycombe Air Park, two aircraft were involved in a collision while preparing for departure from Runway 06. The EV-97 Eurostar Sl Microlight, registration G-CIDZ, was stationary at the holding point for pre-takeoff checks with an instructor and a student on board. Simultaneously, a DHC-1 Chipmunk 22, registration G-ULAS, was taxiing toward the same holding point.

The pilot of the G-ULAS had been instructed by ATC to use a grass taxiway marked by blue stakes. Due to the narrowness of the path, the pilot had been weaving the aircraft from side to side to maintain visibility of the area ahead. After the blue markers ended, the pilot struck a runway holding board, which caused light damage to the aircraft. During this period, the passenger in the G-end noticed the G-CIDZ positioned approximately 3 metres ahead and 2 metres to the right, and alerted the pilot to stop.

The pilot of the G-ULAS brought the aircraft to a halt at roughly a 45-degree angle to the stationary Eurostar. The nose of the Chipmunk was positioned between the right wing and tailplane of the Eurostar. While the Chipmunk pilot prepared to shut down the engine to push the aircraft back, the instructor in the G-CIDZ applied power to move the aircraft forward to avoid what he perceived as an imminent collision. As the Eurostar moved, its right horizontal tailplane and elevator passed through the rotating propeller disc of the G-ULAS, resulting in structural damage to the Eurostar.

The investigation

Investigators examined the taxiing procedures and the visibility conditions at the time of the accident. The investigation established that the G-ULAS pilot had been attempting to maintain a lookout by weaving the aircraft, but this technique proved insufficient once the blue markers disappeared. The investigation also looked into the actions of the instructor in the G-CIDZ, who moved his aircraft forward to avoid a perceived collision, which ultimately led to the contact between the propeller and the tailplane.

Findings

The collision was caused by the Eurostar moving forward into the propeller arc of the Chipmunk.
The pilot of the G-ULAS failed to stop the aircraft immediately after losing sight of the taxiway markers.
The instructor in the G-CIDZ believed moving his aircraft forward would prevent a collision, but this action caused the tailplane to strike the propeller.
The pilot of the G-ULAS was using a weaving technique to compensate for limited forward visibility due to the aircraft's configuration, but this was ineffective once the visual markers ended.