What happened
During an aerotow operation at Långtora Airport, a motor glider, SE-UPH, was towing a glider, SE-TRI, along runway 30. The flight was conducted under northerly winds, which both pilots noted as being turbulent. Shortly after takeoff, the pilot of the towplane experienced a sudden, unexplained nose-down attitude. Despite attempts to pull the nose up, the aircraft failed to respond initially, bringing the plane as low as 26 metres above the ground. The pilot responded by reducing throttle, which eventually restored control and allowed the aircraft to climb.
Simultaneously, the glider pilot observed the towplane dropping unexpectedly and chose to abort the tow by releasing the tow line. Following the release, the glider pilot attempted to perform a short circuit to return to runway 30. During the turn onto the final approach, the glider lost lift, causing the right wing to strike the ground. The impact resulted in substantial damage to the SE-TRI.
The investigation
The investigation focused on the aerodynamic behavior of the aircraft during the tow and the subsequent flight path of the glider. Investigators examined the flight conditions, noting the presence of turbulent crosswinds. The investigation also looked into the mechanical configuration of the aircraft, specifically the use of a center-of-gravity towing hook.
Findings
- The primary cause of the incident was the glider ascending too high relative to the towplane, which caused the tail of the SE-UPH to be inadvertently pulled upward.
- The turbulent crosswind conditions contributed to the instability of the tow.
- The use of a center-of-gravity towing hook was a contributing factor to the flight dynamics.
- The damage to the glider was caused by the pilot's misjudgment regarding the altitude required to complete a full traffic circuit to runway 30.