What happened
On 7 February 2014, a DHC-8-402 Dash 8, registration G-ECOH, was performing a scheduled commercial passenger flight from Birmingham Airport to Belfast City Airport. While cruising at FL220 in visual meteorological conditions near the Isle of Man, the aircraft encountered a sudden and violent onset of turbulence.
During the event, the aircraft's airspeed increased rapidly, causing the autopilot to disconnect and the aircraft to climb to a peak altitude of FL225. The pilot flying took manual control, reduced power, and descended the aircraft back to FL220. While the turbulence eventually moderated to a moderate level, the flight crew initiated a descent for safety.
Inside the cabin, the turbulence caused one cabin crew member to be thrown from her position, resulting in serious injuries. A passenger also sustained minor injuries. The aircraft landed safely at Belfast, where the injured crew member received medical care from a doctor on board before being transferred to a hospital.
The investigation
The AAIB examined flight data recorder (FDR) information, which confirmed that the flight had been smooth until the sudden disturbance. The data recorded a maximum normal acceleration of +2.74g and a minimum of -0.43g. Investigators also reviewed radar data to check for potential wake turbulence from other aircraft, but no other relevant traffic was identified in the vicinity.
Meteorological analysis was conducted by the Met Office to assess the possibility of Clear Air Turbulence (CAT). The investigation reviewed atmospheric models, including wind and temperature gradients, to determine the cause of the instability.
Findings
- The aircraft encountered Clear Air Turbulence caused by significant windshear near the Isle of Man.
- The turbulence was driven by a large windshift resulting from two strong jetstreams (exceeding 100 knots) positioned on either side of the UK.
- While significant weather charts produced 24 hours in advance did not indicate CAT for the specific area, updated meteorological modeling confirmed that the wind and temperature gradients were highly conducive to such an event.
- No structural damage was found on the aircraft following a post-incident inspection.