What happened
On 25 July 2019, a Piper PA-18-150, registration N162AW, was operating from Glenforsa Airfield on the Isle of Mull to various remote locations. While at a field site west of Ben More, at an elevation of roughly 1,500 ft, the aircraft was being prepared for departure. The flight involved two occupants, both of whom held pilot licences.
As the pilot lined up for takeoff, they noted a slight crosswind from the right. During the pre-takeoff phase, the aircraft unexpectedly lifted off the ground. The pilot attempted to maintain control by applying full power and right aileron, but the aircraft rolled to the left. The left wingtip and the nose struck the ground, causing the aircraft to overturn and come to rest in an inverted position. There were no injuries to the two occupants, though the aircraft was destroyed.
The investigation
The investigation examined the aircraft's configuration and the local meteorological conditions. The Piper PA-18-150 was a modified version of the type, featuring large-diameter tyres for unprepared strips and a stalling speed lower than the 40 mph minimum speed readable on the airspeed indicator.
The pilot estimated that a gust of approximately 25 kt would be sufficient to lift the aircraft into the air, noting that at such low airspeeds, the ailerons lack the necessary authority to counteract a rolling tendency once the wind has lifted the plane.
A review of Met Office data indicated that while the weather was generally fine with good visibility, surface wind speeds in the area were likely between 15 and 20 knots. While the Met Office report suggested that gusts were unlikely due to stable air, the investigation considered that local terrain effects could have produced a sudden, strong gust near the ground.