On 16 December 2014, a US-operated Boeing 777-200 encountered a significant period of severe clear air turbulence (CAT) which was unexpected by the flight crew when travelling eastbound over northern Japan at night between FL 270 and FL290. The decision to turn back to Tokyo to allow the nine seriously injured passengers and crew to be treated was made 90 minutes later. The Investigation concluded that the CAT encountered had been correctly forecasted but the Operator's dispatcher-based system for ensuring crew weather awareness was flawed in respect of international operations out of 'non hub' airports.