Flight Conditions
A passenger transport encountered severe turbulence while descending en route to its destination. The flight's forecast had indicated thunderstorm development in the vicinity of the destination. Prior to the event, the crew heard the destination's Automatic Terminal Information Service (ATIS) announce severe turbulence on approach, but they recalled no air traffic control (ATC) advisory stating that the turbulence was severe.
Turbulence Encounter
During the descent, the pilot complied with an ATC request to slow down for traffic separation, which resulted in the aircraft's speed falling below that recommended for turbulence penetration. The aircraft was turning to avoid clouds and virga, with speedbrakes extended and the autopilot engaged when it entered increasing turbulence. The airplane then pitched up 20 degrees and rolled to 45 degrees. The pilot righted the airplane and stopped the descent 500 feet below the assigned altitude.
Aircraft Configuration
Speedbrake extension is known to increase roll rate. The use of the autopilot in severe turbulence is recommended only in the pitch-hold mode.
Additional Information
No injuries or damage were reported in the source. No further details about the aircraft type, registration, engine count, date, operator, location, occupants, or time of day were provided.