THIS ACR MLG FLC DEVIATED FROM THEIR ASSIGNED HDG WHEN THEY MISINTERPRETED THEIR PDC. THE RPTR QUESTIONS THE PRACTICE OF ADJUSTING FLT ROUTING FOR FMC EQUIPPED ACFT WHEN A PRIMARY NAVAID IS OTS.

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PDC READ: FLY RWY HDG VECTOR FOR OASYS2; OASYS2 GFS HEC J64; LAS OASYS2 GFS HEC CIVET CIVET1 LAX. NOTAM 3/1: LAS VOR OTS. I HAVE BEEN FLYING THIS DEP FOR 2 MONTHS; SEVERAL TIMES PER WK. WE LOADED INTO FMS OASYS2 DEP WHICH IS 'HDG 255 DEGS (RWY HDG) TO 3 DME L TURN INTERCEPT 211 DEG RADIAL LAS.' AFTER MAKING OUR TURN SBOUND TO INTERCEPT 211 DEG RADIAL; DEP CTL QUERIED AS TO OUR HDG WHICH WAS 160 DEGS. HE THEN STATED THAT WE WERE TO REMAIN RWY HDG; HENCE OUR DEV FROM CLRNC. CONTRIBUTING TO OCCURRENCE WAS THAT THIS WAS OUR FIFTH AND FINAL LEG FOR DAY. WE HAD BEEN AWAKE SINCE XA00 LCL. FATIGUE WAS INDEED A FACTOR. ALSO; WE SAT AT END OF RWY FOR 22 MINS FOR LAX FLOW CTL. MY PERCEPTION OF THE CLRNC WAS THAT 'FLY RWY HDG; VECTOR FOR OASYS2' IS THAT THE OASYS2 ALREADY HAS YOU FLY RWY HDG TO 3 DME. SO MY MINDSET WAS 'NO CHANGE' THOUGH PDC WAS ANNOTATED -- OASYS2...J64; WHICH MEANT TO ME WE WERE GOING TO RECEIVE EXPEDITED VECTORS LIKE DIRECT HEC OR CIVET. RECOMMENDATIONS: FOR FMS EQUIPPED ACFT; WHY SHOULDN'T WE BE ABLE TO FLY DEP ROUTING BASED UPON PRIMARY NAV FACILITIES NOTAMED OUT OF SVC? IN THIS CASE; THE AMBIGUITY OF THE PDC WOULD BE ELIMINATED IF IT HAD NOT USED THE WORDING OF 'OASYS2' TWICE. CLRNC WOULD HAVE BEEN CRYSTAL CLR IF IT HAD READ 'FLY RWY HDG; VECTORS GFS OASYS2; GFS HEC CIVET CIVET1 LAX.'