Narrative:

The captain and I had returned from break to relieve the flying crew about 1 hour and 45 minutes prior. Had just turned off the center fuel tanks; when about 5 minutes after that heard the warning sound go off which sounded like the autopilot disconnect button. We immediately looked at the instruments and noticed the airspeed was in the red zone and our altitude was off by - 500 feet. The captain reduced the throttles but airspeed continued to increase; so opened the speed brakes slightly. I noticed that yellow slash bars were indicated on both LNAV and VNAV. I told the captain no LNAV or VNAV; engines look fine. The captain disconnected the autopilot while continuing to get the airspeed under control and regain our altitude back to fl 380. I reset the flight directors selected heading select and V/south +300. I then reengaged LNAV/vanv and informed the captain that these systems were available again. The captain turned on the seatbelt sign as a precaution. We were both stunned as to what had happened; because the ride was smooth and had no bumps or chop at all. I immediately got on the radio and told another aircraft behind us (one that we had been communicating with and passing pirep information); that we had just experienced something very; erratic and strange. As I was making this call; a printer message came across the printer about a B777 that had experienced severe wave turbulence at fl 350 in same vicinity we had just traveled. I relayed this info to the aircraft behind us. They informed us yes they had just encountered the same and gained 1000ft; and 50kts. There were other aircraft in the area who later confirmed they experienced the same wave; however; were better prepared to handle it due to our detailed pireps and were very appreciative. We sent a message to dispatch. Dispatch did not show any unusual activity such as horizontal windshear or unusual jet streams in the area so was very surprised to get our prep/report. We later learned that aircraft north of our track did not experience the wave action; but aircraft just south of us did.

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Original NASA ASRS Text

Title: B787 First Officer reported a severe wave encounter at FL380 which resulted in an overspeed and uncommanded 500 foot climb.

Narrative: The Captain and I had returned from break to relieve the flying crew about 1 hour and 45 minutes prior. Had just turned off the center fuel tanks; when about 5 minutes after that heard the warning sound go off which sounded like the autopilot disconnect button. We immediately looked at the instruments and noticed the airspeed was in the red zone and our altitude was off by - 500 feet. The Captain reduced the throttles but airspeed continued to increase; so opened the speed brakes slightly. I noticed that yellow slash bars were indicated on both LNAV and VNAV. I told the Captain no LNAV or VNAV; engines look fine. The Captain disconnected the autopilot while continuing to get the airspeed under control and regain our altitude back to FL 380. I reset the flight directors selected heading select and V/S +300. I then reengaged LNAV/VANV and informed the Captain that these systems were available again. The Captain turned on the seatbelt sign as a precaution. We were both stunned as to what had happened; because the ride was smooth and had no bumps or chop at all. I immediately got on the radio and told another aircraft behind us (one that we had been communicating with and passing pirep information); that we had just experienced something very; erratic and strange. As I was making this call; a printer message came across the printer about a B777 that had experienced severe wave turbulence at FL 350 in same vicinity we had just traveled. I relayed this info to the aircraft behind us. They informed us yes they had just encountered the same and gained 1000ft; and 50kts. There were other aircraft in the area who later confirmed they experienced the same wave; however; were better prepared to handle it due to our detailed pireps and were very appreciative. We sent a message to dispatch. Dispatch did not show any unusual activity such as horizontal windshear or unusual jet streams in the area so was very surprised to get our prep/report. We later learned that aircraft north of our track did not experience the wave action; but aircraft just south of us did.

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.