JAL B763 near Tokyo on Nov 26th 2012, inflight upset injures passenger

A JAL Japan Airlines Boeing 767-300, registration JA610J performing flight JL-877 from Tokyo Narita (Japan) to Shanghai Pudong (China), was enroute at FL360 about 110nm southwest of Tokyo's Narita Airport when an inflight upset caused an injury to a passenger. The crew descended the aircraft to FL280 and continued to Shanghai for a safe landing about 3 hours later.

Japan's Transportation Safety Board (JTSB) opened an investigation into the accident confirming the details but not providing any hint as to what caused the inflight upset.

On May 30th 2014 the JTSB released their final report concluding the probable cause of the accident was:

It is highly probable that this accident occurred because the aircraft encountered the turbulence and was shaken at the cruising altitude of 36,000 ft. This shaking caused one of the passengers who had been away from his seat to lose his body’s balance and to sustain serious injuries.

It is probable that the turbulence the aircraft encountered was caused by the large VWS formed in a temporally and spatially limited narrow range due to the strong southerly warm wind which flowed into the developing front side of the Low.

The JTSB reported that the aircraft was flying in thin cloud with no indications on the weather radar when the captain instructed cabin crew to server passengers with extra care for a while in anticipation of a "little shaking" ahead, after some time in smooth conditions the captain (55, ATPL, 16,048 hours total, 10,247 hours on type) extinguished the fasten seat belt sign. A number of passengers got up to visit the toilets.

About 9 minutes after extinguishing the "fasten seat belt" signs the aircraft encountered severe turbulence producing vertical accelerations between +0.7 and +1.9G. The first officer (36, CPL, 5,240 hours total, 4,953 hours on type), pilot flying, immediately illuminated the fasten seat belt signs and descended the aircraft. After the conditions became smooth again a passenger reported the cabin crew that he had been in the aft toilet and was leaving the toilet when the aircraft encountered the jolts, he had sprained his right ankle (which was later confirmed in hospital as fracture of the right hand ankle).

The JTSB analysed that weather was most likely the primary cause with no involvement whatsoever by crew or aircraft.