What happened
While operating in cruise flight at 22,000 feet, the aircraft encountered unforecast and unexpected clear air turbulence. During this encounter, a flight attendant who was standing was thrown against the bulkhead and subsequently to the floor. The incident resulted in serious injuries to the crew member.
Following the turbulence, the aircraft continued its flight toward its destination and completed the landing without further incident.
The investigation
A review of the flight release provided to the pilots indicated that a warning had been issued for occasional moderate turbulence at altitudes below 12,000 feet. This specific weather advisory applied to an area located several hundred miles west of the aircraft's actual route of flight. Additionally, investigations confirmed that no SIGMETs or AIRMETs had been issued for the area surrounding Roanoke, Virginia, at the time of the event.