What happened
On 17 September 2020, a Bombardier BD700-1A10, registration CS-GLD, was performing a non-revenue positioning flight from Edinburgh to Biggin Hill. The flight crew, consisting of four members, was executing a circle-to-land procedure onto Runway 03. During the final approach, the aircraft was flying at a VREF of 117 kt with the autothroble engaged, though the pilot was hand-flying the aircraft.
As the aircraft entered the flare at approximately 30 ft radio altitude, the pilot increased the nose-up pitch to 9.1°. During this maneuver, the aircraft initially rolled to the left before the pilot applied significant right rudder and right roll control. This input, combined with unidentified external factors, triggered a rapid roll to the right, reaching a peak bank angle of 8.5°. Although the pilot immediately applied a large left roll correction, the aircraft's right main landing gear touched down before the corrective input could stabilize the wings. Consequently, the right wingtip made contact with the runway surface, causing abrasion to the wingtip, aileron, wing leading edge, and the canoe fairings.
The investigation
The AAIB examined the flight data recorder (FDR) and cockpit voice recorder (CVR) to reconstruct the landing sequence. The investigation focused on the aircraft's aerodynamic behavior, the effectiveness of the flight controls at low speeds, and the impact of wind conditions.
Technical analysis by the manufacturer used a six-degree-of-freedom simulation model to evaluate the roll rate and pitch attitude. The investigation also reviewed the manufacturer's recommended landing techniques for crosswind conditions and the operational procedures regarding airspeed increments during turbulence. The investigation confirmed that the autothrottle system functioned as designed and that the aircraft's yaw damper was operating correctly.
Findings
- The aircraft was experiencing a significant crosswind component from the right during the final stages of the approach.
- The pilot applied large right rudder and right roll control inputs during the flare, which contributed to the rightward roll.
- Localized wind or gust effects likely acted in conjunction with the pilot's inputs to increase the roll rate beyond what was caused by control inputs alone.
- The resulting bank angle of 8.5° exceeded the manufacturer's recommended limit of 3° for crosswind landings.
- Roll control effectiveness was reduced by approximately 20% due to the decay in airspeed from VREF to the touchdown speed of 106 kt.
- The combination of a high nose-up pitch attitude and the rapid right roll reduced wingtip clearance to the point of runway contact.