B777-300
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation - Track / Heading All Types; Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter Weather / Turbulence
Flight Crew Took Evasive Action; General Physical Injury / Incapacitation
Weather
We came off our break approximately 4 hrs into the flight. The seatbelt sign was on and the Captain and FO were just finishing a weather deviation at FL280. Shortly thereafter; we encountered light chop and eased the aircraft up to FL290. We had a block of FL280 to FL300. The ride was smooth at FL290. After approximately 15 to 20 minutes of smooth air at FL290 and in the clear with the seatbelt sign on we went from smooth air to severe turbulence in a fraction of a second. We descended immediately to FL280 (in the block) while coordinating for descent to FL250. We were hit a second time with severe turbulence at FL280 and descended with clearance to FL250 while deviating left of course. We descended to FL240 where the ride finally smoothed out. During descent to FL240 the crew rest airflow off light illuminated with a warning chime in the bunks. We felt the turbulence threat overrode the recommendation for the bunks to not be occupied due to airflow. Both encounters with severe turbulence lasted less than a minute. The aircraft was at turbulence penetration airspeed for both encounters. There were no passenger injuries. Two flight attendants were injured.Sleep inertia coming off of a break in the middle of the night was a factor. It was a busy cockpit with finishing a weather deviation; changing altitude for light chop at FL280 and plotting SIGMETs from dispatch. I had taken my iPad to the bunk and gotten up early from the bunk to get the latest weather. There was NO internet connectivity in the cockpit and the turbulence graphic I had pulled up in the bunk disappeared for some reason without the Wi-Fi signal in the cockpit.Wi-Fi that works in the cockpit would certainly have helped. I question dispatching though this particular weather system.
[Report narrative contained no additional information.]
B777 flight crew reported encountering severe turbulence several times until descending to smoother conditions.