B777 flight crew reported encountering severe wake turbulence 20 miles in trail of another B777 on their trans-Pacific flight.
Synopsis
B777 flight crew reported encountering severe wake turbulence 20 miles in trail of another B777 on their trans-Pacific flight.
Narrative
While flying at FL310 and M83 we encountered severe wake turbulence for approximately 10 seconds. Nobody got hurt. We were approximately 20 miles in trail of a 777. Approximately 50 minutes prior to the event; we encountered moderate wake turbulence from the same airplane. We were offset 1 mi right of course; the other 777 was on course and 1000 feet above. The wind was quartering from the left at approximately 30 knots. Both the FO and I were surprised that we hit turbulence of that magnitude despite the fact that the wind was against us. After the first event; we removed the SLOP (Strategic Lateral Offset Procedure) and remained 1000 ft below and 20 mi in trail. The wind had been quartering; however; at the time of the second event the wind display on the ND (Navigation Display) was showing calm wind. When the second encounter happened the onset was almost instantaneous and the turbulence encountered was significant. We did not have time to make a PA announcement as we were both trying to ensure the airplane remained in control; which it did. The autopilot kicked off and the airplane climbed 300 feet. The airspeed fluctuations and pitch changes were not significant. When I regained control of the plane I asked the FO to call the F/A's and check if there were any injuries. All F/A's and PAX were unhurt. After the event; we descended an additional 1000 ft and offset 10 nm left of course. (The wx radar was on and there was no convective activity near us. The turbulence was definitely wake turbulence.). I verbally debriefed with both Dispatch and the Chief Pilot.
Second reporter narrative
I was sleeping in the bunk. All of a sudden everything went flying; including me. I thought 'I hope everyone is okay' and then I fell back asleep. I was later told it was because of wake turbulence from a 777 ahead of us.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.