A B777 FO AND CABIN CREW RPTED SEVERE TURB OVER THE ATLANTIC WHICH CAUSED A SIGNIFICANT LOSS OF AIRSPD REQUIRING THE CREW TO DSND 400 FT.

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WHILE IN CRUISE AT FL360; THE ACFT EXPERIENCED MODERATE TO SEVERE WINDSHEAR/TURB WITH AN ASSOCIATED 50 KT LOSS OF AIRSPD. THE STICK SHAKER ACTIVATED AND A DSCNT WAS INITIATED TO MAINTAIN AIRSPD. TOTAL ALT LOSS WAS 400 FT. ALL PAX AND FLT ATTENDANTS WERE SEATED. NO INJURIES OR DAMAGE TO ACFT. SUPPLEMENTAL INFO FROM ACN 597996: INSTEAD OF JUST VISUALLY MONITORING SEATBELT COMPLIANCE; I ALSO VERBALLY WARNED PAX WE WERE EXPECTING A ROUGH RIDE (SOMETHING I USUALLY DO WHEN COCKPIT FOREWARNS US OF TURB). WE HAD JUST COMPLETED CHKS AND GALLEY SECURITY WHEN WE ENTERED THE TURBULENT AREA. THIS TURB WAS NOT LIKE ANYTHING I HAVE ENCOUNTERED IN 31 YRS OF FLT. THE MOVEMENT WAS VERY SHARP AND ROUGH; AKIN TO DRIVING EXCEEDINGLY FAST OVER A RUTTED ROAD. COFFEEMAKERS BACKED THEMSELVES OUT OF THEIR INSERTS; AND BREW BASKETS FLEW HORIZLY TO OTHER SIDE OF GALLEY. AT THE SAME TIME; YOU COULD FEEL THE NOSE OF THE ACFT MOVE LATERALLY AS WELL AS UP AND DOWN. PAX WERE CRYING AND MAKING SOUNDS YOU ONLY HEAR ON A CARNIVAL RIDE. IF WE HAD NOT RECEIVED ADEQUATE NOTIFICATION; OR HAD CARTS IN THE AISLE; I AM SURE SERIOUS INJURIES WOULD HAVE BEEN SUSTAINED BY PAX AND CREW. WE NEED SOME DEVICE TO SECURE CARTS; WEIGHING UP TO 250 LBS; DURING UNEXPECTED TURB. WE ALSO TOOK EVASIVE ACTION; AS A COMPANY FLT ABOVE US SET OFF OUR PROX ALARM DUE TO UNCTLED ACTION OF THEIR ACFT BECAUSE OF THE SAME TURB. ANOTHER ROUND OF SIMILAR TURB HIT US FOR ANOTHER 10 MINS; THEN SLACKED OFF. I CHKED CABIN; EVERYONE WAS FINE EXCEPT FOR THE USUAL AIRSICKNESS YOU'D EXPECT FROM AN INCIDENT OF THIS PROPORTION. SUN-SPOT ACTIVITY WAS UNUSUALLY HIGH; WOULD THIS HAVE CAUSED AN INCIDENT OF THIS TYPE? SUPPLEMENTAL INFO FROM ACN 598164: I'M OUT ON AN 'IOD' BECAUSE OF MY NECK.