What happened
On 7 March 2017, a DHC-6 Series 310 Twin Otter, registration G-BVVK, was performing a scheduled passenger service from Glasgow to Tiree. The flight, carrying two crew members and seven passengers, arrived at Tiree Airport amidst marginal weather conditions characterized by low cloud and strong southerly winds. Due to the low cloudbase, the crew executed a VOR/DME approach to Runway 23.
Prior to landing, the crew requested several wind updates. The information provided by the Tiree AFISO indicated wind speeds around 23 to 27 knots, which fell within the operator's established 25-knot crosswind limit. The commander took control of the aircraft when the runway became visible at approximately 450 feet. The landing itself was initially perceived as normal, with the pilot noting that control inputs were consistent with the expected crosswind.
However, as the aircraft decelerated during the landing roll, the left wing suddenly lifted and the aircraft veered sharply to the left. Despite the application of full right rudder and left aileron, the aircraft continued to deviate from the centerline for several seconds, crossing a section of grass before the crew managed to bring it to a stop. There were no injuries to the passengers or crew, and the aircraft sustained no damage.
The investigation
The investigation examined the meteorological records at Tiree Airport and compared them with the wind information communicated to the flight crew. While the crew received wind reports that suggested speeds within their operational limits, official Met Office sensors recorded regular gusts reaching approximately 32 knots during the period surrounding the landing.
Investigators also reviewed the aircraft's performance capabilities and the operator's specific landing policies. The investigation noted that the wind information provided to the crew via the Runway 23 touchdown zone indicator did not include the gust components, as the criteria for reporting gusts under CAP 746 (requiring a difference of 10 knots or more from the mean) were not met by the specific wind fluctuations at that time.
Findings
- The crew operated under the belief that the wind conditions were within their permitted landing limits based on the information received.
- A strong gust of wind from the left likely impacted the aircraft during the landing roll.
- As the aircraft's airspeed decreased during deceleration, the flight controls lost sufficient effectiveness to counteract the sudden gust.
- This loss of control authority caused the aircraft to weathercock and depart the paved surface.