MODE CONFUSION BTWN FLC AND FIX INFO ON THE ARR PAGE VICE THE APCH PAGE.

Narrative

I WAS THE PNF ON THIS PARTICULAR LEG OF FLT (PIT-SEA) AND WAS PICKING UP THE SEA ATIS AT 70 NM E OF SEA. WE WERE IN A DSCNT AT THE TIME ON THE GLASR 3 ARR. I NOTICED THE FO HAD GONE TO FLT LEVEL CHANGE MODE AND EXTENDED THE SPD BRAKE. WHEN I INQUIRED AS TO OUR STATUS HE SAID WE WERE GOING TO BE HIGH ON XING JAKSN FIX AND SHORTLY AFTER ZSE RECLRED US FOR A 360 DEG R TURN AND THEN DIRECT JAKSN TO CROSS AT 250 KTS 12000 FT MSL. CLRNC WAS DIRECT MLP; CLRED FOR GLASR 3 ARR TO CROSS JAKSN AT 250 KTS 12000 FT. FMC WAS PROGRAMMED AS FOLLOWS: 1) STAR 'GLASR 3' FROM SEA ARR PAGE WAS SELECTED. 2) TRANS 'MLP' WAS SELECTED. 3) ILS RWY 16R WAS SELECTED. 4) TRANS 'JAKSN' WAS SELECTED LAST. AFTER ATC QUESTIONED WHETHER WE COULD MAKE THE XING RESTR WE CHKED THE LEGS PAGE AND DISCOVERED TWO 'JAKSN' FIXES -- THE 2 FIXES BEING 50+ MI APART. THE LEGS SEQUENCE WAS JAKSN-HETHR-JAKSN AND THE FMC WAS LOOKING AT THE LAST JAKSN FIX FOR THE 250 KTS 12000 FT. WE DID SOME FOLLOW-UP THE NEXT DAY AND IT SEEMS THE PROB STARTS WITH ITEM 3 ABOVE. WHEN ILS RWY 16R IS SELECTED; 3 TRANS ALSO COME UP; WITH JAKSN BEING ONE OF THOSE. WHEN THIS COMBINATION IS ENTERED (ILS RWY 16R; JAKSN TRANS) YOU END UP WITH A JAKSN FMS TRANSITION TO RWY 16R IN THE FMC; AS WELL AS A GLASR 3 ARR. WITH THE PROGRAMMING WE HAD; THE FMC WANTED TO TAKE THE ACFT TO JAKSN THEN HETHR; THEN JAKSN AGAIN TO BEGIN THE INADVERTENTLY PROGRAMMED JAKSN FMS TRANSITION. THE PROB/CONFUSION; I BELIEVE; IS THAT JAKSN IS INVOLVED IN 2 DIFFERENT APCHS -- ONE AS A FIX/INTXN WITH A XING RESTR (GLASR 3) AND THE OTHER AS A TRANSITION FOR AN APCH (JAKSN FMS RWY 16R). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CAPT WAS OFF THE RADIOS OBTAINING SEA ATIS WHEN HE NOTED THE FLYING FO COMMENCED A DSCNT AND THEN WAS QUESTIONED BY ATC IF THEY COULD MAKE THE XING RESTR AT JAKSN. THE FO REPLIED 'YES' AFTER LOOKING AT THE PROGRESS ON THE FMC. BUT; AFTER BECOMING SUSPICIOUS BECAUSE OF THE ATC QUERY; HE LOOKED AT THE 'LEGS' PAGE AND SAW THAT THERE WERE 2 'JAKSNS.' SO; THE FMC WAS COMPUTING THE DSCNT FROM ENRTE TO JAKSN; THEN HETHR AND BACK TO JAKSN. APPARENTLY; AFTER THE GLASR ARR WAS SET IN THE FMC WITH THE JAKSN SPD AND ALT RESTR; AND INSERTING THE ILS RWY 16R APCH ON THE APCH PAGE; THE PROMPT ASKED FOR A TRANSITION; OF WHICH JAKSN WAS ONE OF THE POSSIBILITIES. WHEN SELECTING THE JAKSN TRANSITION FOR THE ILS RWY 16R; THE FMC THEN RTED THE LEGS TO JAKSN; HETHR; AND BACK TO JAKSN. THE CAPT RPTR SAYS THAT IT WAS VERY CONFUSING TO BOTH HE AND HIS FO TO HAVE MORE THAN ONE JAKSN DEPICTED ON THE FMC.