B737-300 ACFT ENCOUNTERED WAKE TURB WHILE 7 MI IN TRAIL OF ANOTHER ACFT ON THE SAME ROUTING STAR. POSTFLT TAPES REVEALED THAT THE LEAD ACFT WAS 200 FT ABOVE RPTR ACFT ALT AT THE TIME OF THE ENCOUNTER.

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JUST AFTER STARTING DSCNT ON ARR INTO SEA AND SLOWING FROM 300 KTS TO 280 KTS FOR CTR REQUEST; THE ACFT PITCHED DOWN AND ROLLED L THEN TO R; FOLLOWED BY PITCH UP. CAPT AND I BOTH JUMPED ON CTL WHEELS TO KEEP ACFT FROM ROLLING. AUTOPLT AND YAW DAMPER WERE TURNED OFF BY CREW AS PER QRH PROCS. AFTER COUPLE OSCILLATIONS WE REGAINED CTL AND CONTINUED TO NORMAL LNDG WITH YAW DAMPER OFF. WE ASKED CTR FOR NEAREST ACFT. SEA SAID 7 NM AT 1200 FT B737. SOME PAX WERE SHOOK UP AS WELL AS CABIN CREW. ACFT WAS GNDED AND MAINT AND FAA AND BOEING NOTIFIED ON AUG/XA/97. CREW WAS NOTIFIED THAT BLACK BOXES WERE PULLED AND EXAMINED AND DETERMINED THAT IT WAS INDEED WAKE TURB. IF IT WAS WAKE TURB; IT WAS COMPLETELY DIFFERENT THAN ANY TURB THAT I HAVE EVER ENCOUNTERED. ALSO IT WAS 7 NM BEHIND ANOTHER B737. MAYBE 1 B737 AT 7 NM BEHIND ANOTHER B737 GIVES OFF MORE TURB THAN RPTED. THIS SHOULD BE LOOKED AT. CORRECTIVE ACTION: THE YAW DAMPER INDICATOR IN THE B737-200/300 IS LOCATED JUST UNDER THE GLARE SHIELD. WHEN PLTS ARE SITTING NORMAL FOR TKOF; LAND (UP CLOSE; FEET ON RUDDER PEDALS); THE SMALL 1 1/2 INCH DIAMETER INDICATOR IS OUT OF VIEW OF BOTH PLTS. THIS SHOULD BE MOVED LOWER ON PANEL SO BOTH PLTS CAN SEE IT IN ALL FLT CONDITIONS. BOEING; FAA; AND MY ACR WON'T AGREE WITH ME BUT I HAVE SPOKEN TO LOTS OF PLTS ABOUT THIS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR FO HAD BEEN OUT OF THE COM LOOP OBTAINING ATIS AND HAD JUST RETURNED WHEN THE ENCOUNTER OCCURRED. CAPT WAS PF BUT BOTH PLTS REACTED TO THE UPSET. CTL WAS MAINTAINED EASILY. AUTOPLT WAS IMMEDIATELY DISCONNECTED AND; THINKING THAT IT MAY HAVE BEEN CAUSED BY THE YAW DAMPER; IT WAS ALSO TURNED OFF. ATC AND BOEING WERE ADVISED AND A PRINTOUT OF THE FLT DATA RECORDER WAS FORWARDED. THE UPSET WAS SO VIOLENT THAT RPTR SAYS HE COULDN'T READ THE GAUGES AND COULDN'T FOCUS HIS EYES FOR 10 SECONDS. RPTR SUSPECTS THAT THE B737-500; WITH ITS LONGER WINGS AND FUSELAGE SIZE MAY CAUSE MORE SEVERE WAKE THAN IS GENERALLY KNOWN. RPTR'S COMPANY MAINT CHANGED THE AUTOPLT; YAW DAMPER AND MCP.