AN ACR MDT FLC PROCEEDED DIRECT TO 'KETCH' INTXN WHEN THEY HAD BEEN CLRED DIRECT TO BUTTE; MT. 'KETCH' WAS THE INITIAL APCH FIX FOR THE ILS RWY 15 AT BUTTE.

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FOLLOWING DEP FROM SEA AND ON A SCHEDULED PAX FLT TO BUTTE; MT; WE WERE HANDED OFF TO ZSE. THE CAPT INDICATED HE WOULD LIKE TO PROCEED VIA RNAV DIRECT TO KETCH INTXN (THE INITIAL APCH FIX FOR THE ILS RWY 15 TO BUTTE). UPON MY REQUEST; WE WERE ISSUED A CLRNC 'DIRECT BUTTE' WHICH I UNDERSTOOD TO MEAN THE ARPT. THE RPTED WX WAS SUCH THAT AN APCH WOULD BE REQUIRED AND I WANTED TO CLARIFY THAT WE WERE CLRED TO COPPERTOWN WHICH IS THE NEAREST VOR FACILITY (AND AT LEAST SERVES AS AN IAF IN THE EVENT OF LOST COMS). CTR DID NOT RESPOND WHEN I READ BACK 'CONFIRM CLRED DIRECT COPPERTOWN.' THE CTLR WAS QUITE BUSY SO I DECIDED TO CLARIFY OR CHANGE OUR CLRNC LIMIT WITH THE NEXT CTR. I ASSUMED WE WERE PROCEEDING DIRECT BUTTE AT THIS POINT; BUT DID NOT CONFIRM THE CAPT'S FMS DATA. THE CAPT SAID 'I'M GOING DIRECT KETCH; WE'LL NEED THE ILS' AND I SAID 'I'LL GET THAT WITH THE NEXT CTLR; I DON'T BELIEVE THIS SECTOR IS FAMILIAR WITH KETCH.' HE AGREED. APPROX 10 MINS LATER I HAPPENED TO GLANCE AT THE FMS WHICH INDICATED A DIRECT COURSE TO KETCH INTXN. WITH 300 MI LEFT ENRTE I AGAIN COMMITTED TO CLARIFYING OUR CLRNC LIMIT WITH THE NEXT SECTOR RATHER THAN CHALLENGING THE CAPT. DUE TO COCKPIT WORKLOAD I NEGLECTED TO FOLLOW THROUGH AND IN FACT CANNOT RECALL IF IT WAS ME OR THE CAPT WHO CHKED ON WITH CTR. APCHING BUTTE; AN HR AND A HALF LATER IT WAS ZLC WHO INQUIRED OUR DEST. I RESPONDED 'DIRECT KETCH.' THE CTLR SAID HE SHOWED US DIRECT 'BUTTE.' THE ZLC CTLR INDICATED THAT THE SEA CTLR SAID HE HAD ONLY CLRED US TO BUTTE. IT WAS UNCLR AT THIS POINT WHETHER THE ERROR TO GO DIRECT KETCH WAS INTENTIONAL OR UNINTENTIONAL TO ME AND NO EXPLANATION WAS OFFERED ABOUT THE MISUNDERSTANDING UNTIL WE WERE ON THE GND. HE ASSURED ME THAT IT WAS HIS 'MISTAKE' AND THAT HE WOULD ACCEPT RESPONSIBILITY. HOWEVER I BELIEVE MY LACK OF CHALLENGE WAS INAPPROPRIATE. CONTRIBUTING FACTORS INCLUDED THAT THIS WAS A FIRST TIME PAIRING FOR US AS A CREW. WE HAD NO ESTABLISHED METHODS OF COM FOR CHALLENGING EACH OTHER AND CONVERSATION WAS LIMITED. COCKPIT WORKLOAD AND CTLR WORKLOAD ALSO INHIBITED CLARIFYING OUR CLRNC LIMIT. WHILE THE RTE DEV CREATED NO KNOWN TFC CONFLICT; I FELT THIS RPT WAS IN ORDER. WHETHER THE CAPT'S DEV WAS INTENTIONAL OR A SIMPLE FMS ERROR I WILL NOT KNOW. THE CREW'S DEV HOWEVER I BELIEVE WAS AT ITS MOST BASIC; A FAILURE OF EFFECTIVE COM AND ALLOWING THE MOST 'TACTFUL' MEANS OF CHALLENGING AUTH TO ENTAIL A DELAY RATHER THAN IMMEDIATE ACTION.