What happened
On 26 January 2017, a Dornier 328-120, registration D-CTRJ, was conducting an EASA certification test flight at Sumburgh Airport, Shetland. The objective of the flight was to verify the aircraft's maximum demonstrated crosswind capability, specifically aiming to increase the limit from 21 kt to 30 kt. The flight crew consisted of two pilots, with an experienced commander acting as pilot monitoring and a test pilot acting as pilot flying.
During the final approach, the aircraft encountered significant wind conditions, with a 24 kt wind gusting to 36 kt from 160°. Upon touchdown, the aircraft landed slightly left of the runway centerline. As the pilot flying attempted to maintain the runway heading by applying left rudder, the aircraft began to drift toward the right side of the runway. In an effort to correct the drift, the pilot applied the left brake. During this maneuver, the pilot inadvertently relaxed the aileron input, causing the aileron deflection to reverse from a right-roll to a left-roll sense. This resulted in the right wing lifting and the right main landing gear leaving the runway surface.
In an attempt to regain control, the pilot moved the power levers forward, intending to reach ground idle, but instead moved them to flight idle, which momentarily increased engine power. Although the pilot monitoring immediately corrected the power to ground idle and applied maximum reverse thrust, the aircraft continued to yaw into the wind. The aircraft eventually left the runway surface and ran onto the grass at approximately 25 kt, where it came to an abrupt stop on the soft ground. There were no injuries to the two crew members or two passengers on board, and no damage was sustained by the aircraft.
The investigation
The AAIB examined the aircraft accident report and analyzed post-flight data provided by EASA. The investigation focused on the sequence of control inputs and the effectiveness of the aircraft's steering systems during the high-wind landing roll. Flight data analysis revealed that aileron deflection reversed significantly during the period when the right main gear lifted. The investigation also looked into the engagement of the nosewheel steering via the nose landing gear weight-on-wheels switch.
Findings
- The pilot flying's attempt to use asymmetric braking led to an inadvertent relaxation of aileron input, causing the right main landing gear to lift.
- The aircraft began to weather-cock into the wind once the right main gear lost contact with the runway.
- Insufficient directional control was available to counteract the strong crosswind conditions.
- The nosewheel steering likely only engaged intermittently during the landing roll, which contributed to the difficulty in maintaining the runway heading.