What happened
On 7 November 2023, a Slingsby Swallow T45 glider, registration BYJ, was engaged in a private ridge soaring flight near Bishop Hill, Kinross. The flight commenced with a winch launch from Portmoak Airfield, reaching an altitude of approximately 1,100 ft agl. The pilot proceeded toward the ridge line, noting the presence of other gliders and paragliders in the vicinity.
As the aircraft approached the hill, the pilot maintained an airspeed of approximately 45 kt. While attempting to fly parallel to the ridge, the aircraft encountered turbulence and a sudden, severe sink rate. Despite an intention to turn away from the terrain, the glider struck the side of the hill and slid through gorse vegetation. The impact caused substantial damage to the cockpit and wings. The pilot sustained serious injuries to the spine and required medical evacuation by air.
The investigation
The investigation examined the flight conditions and the aircraft's performance during the encounter with the ridge. Investigators reviewed the pilot's account of the airspeed and the environmental conditions, including a reported wind of 270° at 8 to 10 kt. Post-accident inspections of the aircraft's control systems revealed no mechanical anomalies or failures in control continuity.
Findings
- The aircraft was flying at an airspeed that was likely below the recommended safety margin for mountain flying.
- The pilot encountered strong sinking air and turbulence while near the ridge line.
- The glider lacked the necessary energy to execute a safe maneuver away from the terrain due to the low airspeed and high sink rate.
- Safety guidelines from the FFVP recommend maintaining a minimum airspeed of 1.45 Vs to provide sufficient energy to navigate windshear or strong sink without stalling.