NTSB Factual Report

While cruising at FL360 in smooth air conditions with no storms in the vicinity, the airplane experienced a 3 to 5 second encounter with clear air turbulence. The seatbelt sign was illuminated at the time. During the event a flight attendant fell and fractured her ankle. Following the brief turbulence encounter, the flight returned to smooth air conditions and later landed uneventfully at its intended destination.

NTSB Probable Cause

The airplane's inadvertent encounter with clear air turbulence during cruise flight, which resulted in a serious injury to a flight attendant.