B757-200 ACFT IN CRUISE ENCOUNTERED WAKE TURB FROM PRECEDING B747 12 MI AHEAD AND CLBING 1200 FT ABOVE RPTR ACFT ALT. RAPID ROLL TO L OF APPROX 48 DEGS; RPTR CLICKED OFF AUTOPLT AND REGAINED ACFT CTL AND DSNDED 700 FT TO GET OUT OF THE WAKE.

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DEPARTED 4 MINS AFTER A B747 FROM GUAM. I WAS CAPT FLYING A B757 ACFT. DURING CRUISE AT FL330 WITH AUTOPLT ON APCHING PAYEE INTXN SPEAKING WITH GUAM CTR ON FREQ 118.7 AT APPROX XZ40Z WE ENCOUNTERED AN ABRUPT ROLL L WITH A BANK ANGLE OF 48 DEGS. RATE OF ROLL WAS VERY FAST. INITIALLY APPEARS AS CLR AIR TURB. I TURNED OFF AUTOPLT DURING RECOVERY AND PUSHED NOSE DOWN TO ESCAPE THE ROLL AND ALSO RECOVER. WE DSNDED QUICKLY TO 32300 FT AND ADVISED ATC OF THE SIT AND THAT WE WOULD RETURN TO FL330. WE PROMPTLY RETURNED TO FL330. DURING THE RECOVERY I ALSO CONSIDERED A POSSIBLE VORTEX OR JET WASH FROM THE PRECEDING B747 WHICH WAS CLBING AHEAD OF US TO FL370. TCASII SHOWED THE B747 1200 FT ABOVE OUR ALT AND 12 MI AHEAD OF US. WE HAD NO DAMAGE OR INJURIES WHATSOEVER. ONLY SPILLED 2 MEALS IN THE FIRST CLASS GALLEY. AGAIN; NO INJURIES OR DAMAGE. CALLED UP FLT ATTENDANTS AND DEBRIEFED CREW. NOTIFIED COMPANY AND FILLED CAPT'S IRREGULARITY RPT. SUGGEST AN ADVISORY LETTER TO PLTS WARNING OF THIS SIT. WE WERE QUICK. I BELIEVE IT COULD HAVE EASILY BEEN MUCH WORSE. NO CONTRAILS AT THE TIME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALLBACK IN CONJUNCTION WITH WAKE TURB INCIDENT QUESTIONNAIRE. RPTR CAPT WAS VERY INTERESTED IN COOPERATING. HE HAD NO PRE-WARNING OF THE IMPENDING WAKE ENCOUNTER; BUT HAD SEEN THE OTHER ACFT PERIODICALLY AND HAD IT ON TCASII. PRIOR TO THE ACTUAL WAKE JOLT THEY EXPERIENCED WHAT APPEARED TO BE A LOW RUMBLE SIMILAR TO MACH BUFFET AND THEY HAD BEEN IN LIGHT TO MODERATE TURB. RPTR FIRST THOUGHT THEY HAD ENCOUNTERED CLR AIR TURB; BUT THEN AFTER THE EVENT SAW THE WINGTIP VORTICES IN THE WISPY CLOUDS OF THE B747 AND; BECAUSE THE B747 WAS CLBING WITH MAX PWR; IT BECAME MORE EVIDENT THAT THE TURB WAS CAUSED BY B747 WAKE. RPTR THINKS THAT FLCS SHOULD HAVE GREATER FLEXIBILITY IN THE OCEANIC SYS TO ALTER COURSES AND/OR ALTS TO AVOID SUCH EVENTS. HE WAS COUNSELED THAT IN FACT IT WILL HAPPEN IN THE FUTURE WHEN FANS IS IMPLEMENTED.