Primary finding
Probable cause
The airplane’s inadvertent encounter with convective turbulence.
Investigator assessment
Analysis narrative
The airplane was in cruise flight when it encountered convective turbulence at flight level (FL) 320. Weather conditions were dark moonless night with scattered storms visible on radar, but the crew reported no returns along their path. A Convective SIGMET was in effect for the area which forecast cloud tops to FL320. The cabin crew was conducting drink service. The flight crew stated they unexpectedly entered a cloud and experienced moderate to borderline severe turbulence. The C flight attendant fell and broke her ankle.