What happened
On 21 June 2002, a modified Piper PA-22-160 Tri-Pacer, registration G-BSED, was performing a private flight from a private airstrip at Cheyne Farm, Stonehaven. During the takeoff roll, the aircraft was experiencing surface winds of 10 to 13 knots, which were varying in direction. As the aircraft reached a speed of approximately 50 mph, a gust from the left caused the plane to veer leftward.
Despite the pilot attempting corrective control, the aircraft began to oscillate between left and right. The left main wheel subsequently left the grass runway and entered an area of long grass. The aircraft then veered sharply to the left and struck a wire fence located roughly 13 metres from the runway centreline. Upon impact, the left main wheel fell into a furrow, causing the landing gear to collapse. This impact caused the aircraft to slew 80 degrees to the right before coming to a halt. There were no injuries to the pilot or the passenger, though the aircraft sustained significant damage to its engine, cowling, propeller, elevator, landing gear, left wing, and left main wheel.
The investigation
The AAIB examined the runway conditions and the physical characteristics of the airstrip. The pilot noted that the grass on the side of the runway was between six and eight inches long, which is typical for the summer months. The investigation also reviewed safety guidance regarding unlicensed aerodromes, specifically CAP 408 and the 'Strip Sense' leaflet.
It was noted that for runways shorter than 800 metres, the recommended minimum width is 18 metres, with a runway strip extending 30 metres on either side of the centreline. Furthermore, safety guidance suggests that grass length should not exceed 30% of the wheel diameter to avoid excessive drag. The investigation found that the aircraft's excursion was triggered by the interaction between the wind gust and the runway environment.
Findings
- The aircraft veered due to a gust of wind from the left during the takeoff roll.
- The aircraft left the prepared surface and entered long grass, which increased drag and contributed to the loss of directional control.
- The aircraft struck a wire fence, leading to the collapse of the left landing gear.
- The grass height on the runway margins was significantly higher than recommended safety thresholds for wheel diameter.
- The owner of the airstrip has since expanded the lateral dimensions of the runway and the surrounding runway strip.