B777 Undifferentiated or Other Model
Flight Crew Last 90 Days 180; Flight Crew Total 18000; Flight Crew Type 1000
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Weather
Aircraft encountered sudden severe CAT. clearly Jet stream activity. Autopilot disengaged and aircraft descended from FL330 to FL320. Full power added and RJJJ [ATC] notified. QRH procedure accomplished. There was no build up; smooth to immediately severe. Seat belt had been placed on earlier because the flight ahead had encountered some turbulence a bit earlier. The horizon was reported as visible; no clouds; and the WX radar had no echoes. The only report of turbulence had been about an hour previous and at a point behind the aircraft. Sabre WX chart had shown turbulence during the climb and into Korean/Southern Japan airspace which was mostly light; but nothing indicated in this area. No injuries but later 2 flight attendants told me they were a bit sore from holding on to the aircraft. note: I was Capt of this flight and the First Officer and I were in the bunk at the time. I woke up during this and very shortly after we climbed into very smooth air. It apparently was worse in the rear of the aircraft.
At PUTER intersection on A590 we encountered severe clear air turbulence. The turbulence caused a high speed warning; then a rapid loss of airspeed and a 1000 foot altitude deviation. We immediately reported the turbulence and altitude to atc; returned to assigned altitude and requested new altitude. Also informed company Maintenance of event. Referenced turbulence action guide in QRH. No damage or injury was reported.
B777 Flight Crew reports encountering severe clear air turbulence in RJJJ airspace; causing an overspeed warning initially then a 1000 foot altitude loss. The crew is able to return to the assigned altitude then to FL350 for a smooth ride. No injuries are reported.