Incident Overview
USAir Flight 95 was climbing to FL350 when it encountered light chop. The crew leveled at FL310 and kept the seat belt sign on. After inquiring about turbulence ahead, they were advised of reported light to moderate chop and one encounter with severe turbulence at FL260. The flight was cleared to descend to FL240. During the descent, the aircraft encountered severe turbulence. The captain declared an emergency and continued the descent to FL200. The captain noted that the turbulence lasted approximately 1.5 minutes between FL270 and FL210. There were no clouds, and visibility was unlimited at night. The flight attendants were unrestrained; one was seriously injured and three received minor injuries.
Weather Conditions
A SIGMET was in effect that forecast moderate to occasional severe turbulence between FL240 and FL350 in an area west of the aircraft's flight path. A weather study showed that the turbulence was encountered where subtropical and polar jet streams converged.
Investigation Findings
Investigation revealed an inconsistency in the dissemination of Center Weather Advisories (CWAs) and SIGMETs. Although CWAs and SIGMETs had the same level of priority for air traffic control and flight service station use, CWAs were not disseminated over 604 and 135 weather circuits. USAir received weather information via the FAA's 604 and 135 circuits, so the airline did not have CWA information for weather briefings.