What happened
On 8 June 2006, a DHC-8-402 Dash 8, registration G-JEDM, was performing a public transport flight from Newcastle to Exeter. While descending through cloud at approximately 9,338 ft, the aircraft encountered sudden and severe turbulence that had not been predicted in the meteorological forecasts.
At the time of the encounter, the aircraft was travelling at 260 kt. The intensity of the turbulence caused the autopilot to disconnect automatically. The pilot responded by maintaining wings level and reducing engine power to manage the aircraft's attitude. During the 15-second event, the aircraft's speed dropped to 240 kt, and a maximum vertical acceleration of 2.285g was recorded.
While passengers had been secured in their seats for landing, the two cabin crew members were still unseated. One crew member managed to secure themselves in a passenger seat, but the second crew member, who was in the rear galley, was unable to reach a seat. This crew member was lifted off the floor twice by the turbulence, landing heavily on their right ankle during the second impact, resulting in a broken ankle.
The investigation
The AAIB examined the flight data and the circumstances surrounding the turbulence. The investigation confirmed that the weather radar had not been active at the time of the encounter. Meteorological reports for the area indicated scattered clouds and moderate turbulence between 3,000 and 4,000 ft, but the specific severe turbulence encountered by the aircraft was entirely unexpected.
Engineers subsequently inspected the aircraft and found no structural damage resulting from the event. The investigation also reviewed the operator's standard operating procedures (SOPs), which dictate that the seat belt sign should be activated and passengers secured ten minutes before landing. The investigation noted that the aircraft's speed during the turbulence was 50 kt higher than the recommended speed for severe turbulence conditions.
Findings
- The turbulence encountered by G-JEDM was unforecasted.
- The aircraft was flying at a speed significantly higher than the recommended speed for severe turbulence.
- The high airspeed likely exacerbated the effects of the turbulence within the cabin.
- The cabin crew member's injury was caused by being lifted and dropped heavily due to the turbulence while unseated.