WAKE TURB -- IN CRUISE.

Narrative

SEA-LAX. JUST PRIOR TO DSCNT PHASE AT ABOVE LISTED POS; ACFT ENCOUNTERED SEVERE WAKE TURB. ACFT BEGAN TO SHAKE; THEN ROLLED RAPIDLY TO L TO APPROX 50-55 DEG ANGLE OF BANK. THE NOSE DROPPED; AUTOPLT HAD DISCONNECTED; AND BOTH PLTS TOOK MANUAL CTL OF ACFT. WINGS WERE LEVELED WITH LOSS OF 300 FT ALT. AS CAPT; I CONTACTED ZLA TO INFORM THEM OF OUR ENCOUNTER AND ASKED IF THERE WAS ANY TFC AHEAD. THEY INFORMED US THAT WE WERE FOLLOWING A B- 747 INTO LAX. I REQUESTED A HDG DEV AWAY FROM TRACT OF THE 747 AND SEPARATION FROM THE 747. I CONTACTED THE FLT ATTENDANTS TO CONDUCT A CABIN CHK OF THE PAX. THEY RPTED NO INJURIES. I EXPLAINED TO THE PAX WHAT HAPPENED AND CONTINUED TO LAX FOR A NORMAL LNDG. ZLA QUALITY ASSURANCE PERSONNEL WERE CALLED AS WELL AS MGMNT PERSONNEL TO COORDINATE A FOLLOW-UP EVALUATION OF THIS INCIDENT. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE B747 WAS DSNDING AND WAS 10 MI AHEAD OF THE RPTR'S MD-80. THE FIRST INDICATION OF THE WAKE WAS A SLIGHT 'RUMBLE' IN THE MD80'S AIRFRAME. THEN THE AUTOPLT DISCONNECTED AS THE MD80 ROLLED 60 DEGS TO THE L AND LOST 200-300 FT. BOTH THE FO (WHO WAS FLYING) AND THE RPTR (CAPT) GRABBED THE CTLS AND RECOVERED THE ACFT AND CLBED BACK TO FL330. ONLY AFTER THEY INQUIRED DID THE ARTCC RADAR CTLR TELL THE CREW ABOUT THE B747. THE RPTR THEN REQUESTED TO BE VECTORED OFF-TRACK FOR THE REST OF THE LEG TO LAX. THIS EVENT OCCURRED ABOUT 60 MI NW OF FIM. THE RPTR SUGGESTS THAT THE WAKE TURB ADVISORY PROGRAM BE EXPANDED TO INCLUDE ADVISORIES DURING CRUISE AS WELL AS THE TFC PATTERN AND FINAL APCH. HE SAID THAT THE FLC TEMPORARILY LOSS CTL OF THE ACFT AND THE FLT ATTENDANTS AND PAX WERE BADLY FRIGHTENED. ONE COUPLE; WHO WERE SCHEDULED TO CONTINUE TO MEXICO; INSTEAD TOOK THE TRAIN BACK TO SEA. THE RPTR FURTHER STATES THAT; AT THE TIME OF THE ENCOUNTER; THEY WERE CRUISING AT .78 MACH AND USUALLY ZLA STARTS SLOWING EVERYONE DOWN AROUND THIS AREA. IF THE ACFT HAD BEEN AT A MUCH LOWER SPD THEY WOULD HAVE STALLED AND LOST A GREAT AMOUNT OF ALT DURING THE RECOVERY.