What happened
Approximately three hours before departure, a dispatcher approved a flight release that included SIGMET Whiskey 8, which indicated occasional severe turbulence between 14,000 feet and FL 280. At that time, the turbulence area covered the departure airport and the planned climb altitude, though the top of descent and the destination remained clear.
After the pilot printed the flight release, the weather information had been updated to SIGMET Whiskey 9. This update moved the turbulence area east of the departure airport, leaving both the top of descent and the destination outside of the affected zone. The release also included a single pilot report of severe turbulence from a Boeing 737 at FL 240 within that same area.
Following the signing of the flight release but prior to departure, the weather was updated again to SIGMET Whiskey 10. This change shifted the turbulence box further east, such that it now covered both the top of descent and the destination airport.
As the aircraft approached its destination, the pilot descended into the area defined by both SIGMET Whiskey 9 and Whiskey 10. The turbulence zones spanned from Ottawa, Canada, to Florida and Cleveland, Ohio. Prior to the encounter, the pilot had activated the seat belt sign, instructed the flight attendant to be seated, and announced that passengers should remain seated as the aircraft was within 30 minutes of arrival. While descending through 17,800 feet, the aircraft encountered severe turbulence.
The investigation
The aircraft was not equipped with ACARS. Under existing procedures, flight crews were required to monitor dispatch frequencies for updates and were encouraged to obtain weather updates while en route. These updates were performed via direct radio contact between the dispatcher and pilots or by the pilots accessing FAA facilities during the flight. Records indicated that while the operator had approximately 100 flights operating within the turbulence box, none were cancelled due to forecast turbulence or reported to have encountered severe turbulence prior to this event.