Date: 201706
Local time of day: 1201-1800
Location: VHHH.Airport, FO
Flight conditions: VMC
Weather elements / visibility: Thunderstorm; Turbulence
Light: Daylight
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: Center ZGZU
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Relief Pilot
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: Pilot Flying; Relief Pilot
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; General Physical Injury / Incapacitation
Contributing factors: Weather; Human Factors
Primary problem: Weather

Narrative: On descent into VHHH about an hour from planned landing we picked up a broken line of TSRA on radar on our route into VHHH. I was a relief pilot and PM and had just called to get the flying pilots back up to the cockpit. It appeared we would be near the line of storms that ran E-W and were moving little in about 20 mins. We expected the flying pilots back in the cockpit in the usual 10. We had been advised by dispatch to expect 20 mins of holding in VHHH; so fuel reserves were a consideration; as they always are on this flight I understand. We saw a nice gap between cells that looked safe (as the storms were not too big and basically stationary) and we decided on a slight left/right jog off of our route to get through what radar depicted as a several mile gap in cells. My guess is highest tops around FL330. About 15 mins out we called the purser and advised him that moderate turbulence was possible in 15 mins also turned on the seatbelt sign and made the PA. As a precaution about 3-4 mins out we advised the 'Flight Attendants; take your jumpeasts.' Although we didn't speak directly to the other pilots; I personally felt that this would be sufficient warning to either sit and delay returning to cockpit or expedite it; plus we had told the purser what was happening and felt like he had the info to pass along to pilots coming off of break while we were busy flying. I asked the flying pilot (and PIC) if he wanted me to call them and let them know to get up front; but he didn't think it was necessary. Meanwhile the controller advised that for us to descend from FL320 to FL270 (in meters); 2000 FPM in the descent and 300 knots. He had been keeping us busy with gradual descent clearances of about 1000-2000 meters; route offsets; etc. We are now pretty task saturated: Chinese ATC; Weather; crew change/cabin communications; meters conversion; end of long flight; etc. Fatigue wasn't a huge issue but looking back it may have harmed communications. At the exact same time that we approached the gap the chime for pilots returning to the flight deck occurred and the pilot flying instructed me to let them in I elected to stay in my seat until we were past the weather just as the flying pilot slightly misjudged the turn and we wound up grazing the edge of one of the cells at FL270 and for about 5-10 seconds we found ourselves in severe turbulence at about 280-290 knots. We were already turning away from the cell. There was a gain in alt in an updraft; but I don't know how much and we could hear precipitation hitting the glass. We quickly returned to assigned after clear of weather. Also; after we were well clear of the weather (1 min) we called back to ask about the crew; purser said he thought FA in back might have been injured; and that he was checking; as the two pilots at the cockpit door and two FAs in back were not seated at the time of the encounter. All other FAs and Passengers were seated and later the FAs said they had to encourage passengers to sit. When it was clear that we were clear of the Weather I got up and check on Captain and flying FO and let them in the cockpit. Pilots were slightly shaken up but uninjured and we swapped seats as normal. They said that they had been delayed in returning to the cockpit by elderly folks using the first class lav. After we landed we checked with the purser and he told us that we had given the FAs in the back ample warning to take their jump seats. One FA did seek medical attention for a bump on the head and we had radioed station to be ready to assist her. They said that things happen and we debriefed both at the gate and on the ride to hotel about what we might do differently next time. For my part; I would definitely have called back and let the pilots know directly what was happening; and knowing what I know now advocated a much larger diversion around the area of weather; although it was difficult to determine how long the line was and we were very close to having this be a non-event. Honestly; it seemed that the course we selected looked as good as any of our other diversion options at the time. Still in hindsight; I would have advocated something else. Also; I would have stated why the seat belt sign was coming on early to make sure that everyone understood that being seated was paramount; and that this wasn't just the usual prior to landing seat belt call. This would also have let the pilots on break know exactly what was happening so they could come up and assume the flying duties; or been someplace other than just behind the door. The Captain accomplished the turbulence write-up; we held on our way in and we landed with 5000-6000 lbs less than planned on the fuel; around 18;000 lbs remaining I think.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B777 flight crew reported anticipating turbulence ahead due to thunderstorms and informed the flight attendants and passengers to take their seats and fasten their seatbelts. Two flight attendants did not and were slightly injured by severe turbulence.