What happened
On 13 March 2023, a DHC-6 Series 310 Twin Otter, registration G-CBML, was performing a scheduled passenger flight from Land’s End to St Mary’s Airport in the Isles of Scilly. After several earlier cancellations due to high winds, the crew proceeded with the flight as reported wind speeds had dropped within operational limits.
During the visual approach to Runway 27, the aircraft encountered significant wind fluctuations. Although the initial touchdown was smooth, the aircraft began to float down the runway. As the crew attempted to stabilize the aircraft, the right wing lifted, followed by a violent rise of the left wing. The aircraft began to veer left and weathercock into the wind, eventually traveling onto the nose and right main wheels.
Recognizing the loss of directional control as the aircraft approached the edge of the runway, the commander initiated a go-around by applying full power. The aircraft traveled approximately 12 metres across the adjacent grass before becoming airborne. After climbing away, the crew performed a second, uneventful approach and landed safely. There were no injuries to the 15 passengers or 2 crew members, and no damage was sustained by the aircraft.
The investigation
The AAIB examined the flight sequence, meteorological data, and aircraft controls. Investigators noted that while the aircraft was within crosswind limits, the landing occurred during a period of gusty conditions. ATC reports indicated a headwind of approximately 10–15 kt and a left crosswind of 16–23 kt.
Witnesses, including local pilots, observed two significant wind gusts punctuated by a short lull during the landing phase. The investigation also reviewed the aircraft's configuration, noting the commander had elected to use full flaps to ensure the aircraft could stop within the available runway distance, despite the potential benefits of using Flap 20 in such winds.
Findings
- The aircraft experienced a sudden change in wind stability, likely due to a lull in the wind followed by an increase in wind strength.
- It is probable that the commander's attempt to correct the right wing's lift by reducing in-to-wind aileron left the aircraft with insufficient control to counteract the subsequent wind increase.
- As airspeed decreased, the flight controls became less effective, leading to the aircraft veering off the paved surface.
- The commander's rapid decision to execute a go-around prevented a more serious excursion.