What happened
On 13 April 2017, a YAK-52, registration G-SPUT, was involved in an accident at Brown Shutters Airfield in Somerset. Following a routine landing on Runway 33, the pilot taxied the aircraft beyond the designated grass runway surface. While attempting a left-hand turn at an estimated ground speed of 20 to 25 mph, the aircraft began to slide sideways to the right. The aircraft moved down a grass slope and struck a mound, causing it to tip onto its nose and a wingtip. The incident resulted in no injuries to the pilot, though the aircraft sustained damage to the propeller, engine, and wing.
The investigation
The investigation examined the aircraft's steering mechanics and the environmental conditions at the time of the accident. The nosewheel of the YAK-52 is not steerable; instead, directional control during taxiing relies on differential braking, where the rudder mechanism regulates pneumatic brake pressure to the left and right brakes. At low taxiing speeds, the aerodynamic effectiveness of the rudder is primarily dependent on airflow generated by the propeller.
Investigators noted that the airfield's website describes the location as a challenging environment due to limited landing distances. While infrastructure works were being conducted near the end of the runway on the day of the accident, the pilot did not identify these as a factor. The weather was reported as dry with 10 km visibility and light, variable winds.
Findings
- The pilot's attempt to turn left resulted in a lateral slide down a grass slope.
- The braking system was found to be functioning correctly with no technical faults reported.
- The slippery nature of the grass rendered differential braking ineffective for maintaining directional control.
- The pilot failed to sufficiently account for the slope of the terrain and the lateral forces acting on the aircraft during the turn.