What happened
On 3 March 2009, a DHC8-402 Dash 8 Q400, registration G-JEDM, was conducting a scheduled passenger flight from Edinburgh to Southampton. While descending through 6,000 ft, the aircraft encountered moderate to severe turbulence and an ice detection message.
As the aircraft turned towards the base leg, the airspeed decreased steadily. During this period, the crew selected flap 5, but the deceleration continued until the aircraft reached a minimum speed of 147 kt. This drop in speed triggered the stick shaker warning and caused the autopilot to disengage. Following the warning, the aircraft' 12.5° nose-up pitch and 43.5° left bank increased significantly. The flight crew eventually regained control, and the airspeed recovered to approximately 175 kt before the autopilot was re-engaged.
The investigation
The AAIB investigation examined flight data recorder (FDR) information, which revealed that the aircraft was in an 'icing configuration' with the REF SPEEDS switch set to INCR. This setting increases the minimum operating speeds to account for potential aerodynamic changes. The investigation also reviewed the crew's actions, noting that the commander had set the REF SPEEDS switch to OFF shortly after the stick shaker activation, rather than performing standard stall recovery procedures.
Findings
- The aircraft's airspeed fell below the minimum safety margin for the configuration, causing the stick shaker to activate.
- The crew's workload was increased by heavy rain, turbulence, and an Air Traffic Control instruction to reduce speed to 160 kt.
- The co-pilot did not provide immediate manual control inputs to correct the bank angle after the autopilot disengaged.
- The commander's focus was divided by radio communications and the upcoming flap selection.
- The aircraft's configuration and the high tailwind contributed to the rapid deceleration.