WPR11LA139

As the airplane descended from about 38,000 feet, the flight crew observed that they had a tailwind of between 60 and 70 knots and that cumulonimbus clouds were ahead of the airplane. Descending through 34,668 feet, the tailwind suddenly decreased and the indicated speed of the airplane quickly increased. The captain activated the speed brakes and disengaged the autopilot. Subsequently, the airplane began to slow. As the captain was slowly retarding the speed brakes, the airplane started to climb and the captain slowly lowered the nose of the airplane. The digital flight data recorder revealed that over a 30-second period the airplane’s vertical acceleration decreased to 0.75 g, then increased to 2.33 g, decreased to 0.05 g, then stabilized at 0.9 g (normal). During the event, one passenger broke her femur; two cabin attendants and four passengers received minor injuries. The airplane was not damaged. Convective activity was located immediately west of where the event occurred, likely blocking the wind flow and causing a wave-like disturbance downstream of the storms, which would result in unanticipated convectively induced turbulence. Since the event occurred in clear air downstream of the cumulonimbus clouds, the airplane likely encountered an undulating turbulence under a strong temperature inversion and strong windshear. The turbulence was not predicted by weather forecasters.

On February 10, 2011, at 0830 Hawaiian standard time (HST), a Boeing 767-300, Japan registry JA603J, while descending through 34,668 feet mean sea level (msl), experienced a turbulence event 4 miles south of Ni'ihau, Hawaii. Japan Airlines International Co, Ltd., operated the airplane as a commercial passenger flight, JAL074, under the provisions of Title 14 Code of Federal Regulations Part 129. The flight crew was not injured. One passenger was seriously injured; two cabin attendants and four passengers received minor injuries. The airplane was not damaged. Visual meteorological conditions prevailed, and an instrument flight plan had been filed. The flight originated from Narita, Japan. The flight crew reported that after starting the descent from 38,000 feet, they observed the tailwind increase from about 60 knots to about 65-70 knots, along with cumulonimbus clouds located in front of the airplane. As the airplane descended through about 34,668 feet, they observed the tailwind suddenly drop and the airplane’s speed quickly accelerated. The captain pulled the speed brake, disengaged the autopilot, and the airplane gradually began to slow. As the captain slowly retarded the speed brake, the co-pilot stated that the airplane was starting to climb. Subsequently, the captain slowly started to pitch the nose of the airplane down. During the event, one passenger received a broken femur. The passenger was located outside of the aft lavatory when she felt her body sink and she fell onto the floor; she collided with cabin objects throughout the turbulence event. A cabin attendant was located in the aft galley when she felt her body float halfway up to the ceiling and then she fell onto her knees. Her body floated up a second time and she struck her head on the ceiling; subsequently, she fell onto the right side of her body, striking her face and elbow on the floor but was not seriously injured. The Japan Transport Safety Board (JTSB) downloaded the data from the airplane’s digital flight data recorder (DFDR) and provided it to the National Transportation Safety Board’s (NTSB) Vehicle Recorder Laboratory. According to the DFDR data, the event occurred at 18:30.05 UTC (0830 HST); at this time, the airplane was descending through 34,964 feet mean sea level (msl). The vertical acceleration decreased from approximately 1 g to 0.76 g’s in less than 1 second, approximately 6 seconds later at 8:30:11, the vertical acceleration peaked at 2.33 g’s while the pressure altitude leveled at approximately 34,634 feet msl. About 2 seconds later at 8:30:13, the vertical acceleration decreased to 0.05 g’s and approximately 22 seconds later at 8:30:35, the vertical acceleration settled back to approximately 0.9g. A weather synopsis produced by a NTSB meteorologist revealed convective activity approximately 20-40 miles west of where the event occurred. Satellite imagery indicated several high level cirrus cloud bands moving eastward towards where the event occurred. TheLihue sounding revealed a level of maximum wind from 280° at 71 knots at 38,000 feet. At 34,000 feet the wind was estimated from 294° at 49 knots with a temperature of -46° Celsius (C). The event occurred in clear air, downstream of cumulonimbus clouds, within a strong temperature inversion and wind shear. No turbulence was predicted by weather forecasters where the event occurred.