B777 flight crew reports encountering severe clear air turbulence in rjjj airspace; causing an overs...

Narrative:

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.

Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1217425
Time
Date	201411
Local Time Of Day	1801-2400
Place
Locale Reference	RJJJ.ARTCC
State Reference	FO
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B777 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Oceanic
Flight Plan	IFR
Person 1
Function	Captain
Experience	Flight Crew Last 90 Days 180 Flight Crew Total 18000 Flight Crew Type 1000
Person 2
Function	Pilot Flying First Officer
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Speed All Types Inflight Event / Encounter Weather / Turbulence

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.