ZAB CONTROLLER QUESTIONS A320 FLT CREW ABOUT THEIR EARLY TURN APPROACHING A NAVAID TO THE OUT BOUND LEG WITH A 90 DEGREE HEADING CHANGE.

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THIS EVENT OCCURRED BECAUSE ATC EXPECTS US TO FLY CLOSER TO THE CTR OF THE AIRWAY THAN REQUIRED BY THE AIM AND BECAUSE WE CHOSE TO ALLOW THE ACFT TO FLY TO THE LIMITS OF THE AIM. ATC KEPT US ON THE 100 DEG HDG FOR QUITE A DISTANCE THEN CLRED US DIRECT TFD AS FILED. THIS GAVE US ABOUT A 90 DEG TURN OVER TFD TO THE 121 DEG OUTBOUND TO TUS. I WAS CONCERNED ABOUT THE WIDE TURN THE AUTOMATION WAS PLANNING TO MAKE AT TFD; AS I RECALLED THERE WERE PROBS WITH THE OLD GOFFS INTXN OUT OF LAS YRS AGO. I MENTIONED THIS TO THE FO AND THEN HAD A CLOSER LOOK ON THE NAV DISPLAY; WHICH INDICATED THAT WE WOULD REMAIN JUST WITHIN 4 MI OF THE AIRWAY IN THE TURN. ABOUT 7 MI FROM TFD; WHICH IS A MI OR TWO AFTER THE A320 STARTED THE TURN; ATC CONTACTED US TO ASK WHERE WE WERE GOING. WE REPEATED OUR CLRNC AND ASKED THEM TO VERIFY. ATC POINTED OUT THAT WE WERE ALREADY STARTING OUR TURN; WHICH WE KNEW TO BE NORMAL FOR THE AIRBUS; BUT DIDN'T CLRLY SPELL OUT WHAT THEIR CONCERN WAS. RATHER THAN GET IN AN ARGUMENT; I ASKED FOR A HDG. ATC REFUSED AND STATED THEY WANTED US TO FLY OUR CLRNC AND TO EXPEDITE OUR CLB FOR TFC. AT THIS POINT WE WERE STILL WITHIN THE AIRWAY. WE COMPLIED WITH THE CLB AND GUESSING THE WIDE TURN WAS THE ISSUE; WE PUT THE ACFT ON A HDG TO TFD AND THEN MANUALLY ENTERED A HDG FOR THE OUTBOUND. ONCE OUTBOUND; WE SELECTED MANAGED NAV. WE ARE GUESSING THAT THIS WAS THE PROB; SINCE ATC NEVER CAME RIGHT OUT AND SAID WHAT THEY WANTED OR NEEDED FOR SEPARATION. THIS IS ONE OF THOSE STANDARD AIRBUS 'ISSUES.' OF COURSE IN THE FUTURE; WHEN MAKING A TURN ON AN AIRWAY GREATER THAN 70 DEGS; OR SO; I'LL USE THE HDG MODE. THIS IS THE MAIN CHANGE TO BE MADE. ATC SHOULD BE MORE AWARE OF THIS ISSUE OVER TFD THE WAY THEY ARE OUT BY LIDAT. MORE IMPORTANTLY; AND I'VE SEEN THIS IN MANY INSTANCES; IT IS VERY IMPORTANT THAT WHEN AN ACFT IS GOING SOMEWHERE A CTLR DOES NOT WANT IT TO GO; THAT THE CTLR GET THE AIRPLANE WHERE IT NEEDS TO BE USING UNAMBIGUOUS HDGS AND ALTS. THEN; AFTER LETTING THE CREW KNOW THEY ARE OUT OF THE CONFLICT; CONVERSE ABOUT THE MISUNDERSTANDING. WHAT HAPPENED IN THIS CASE IS WE WERE TOLD TO GET BACK ON OUR CLRNC. WE THOUGHT; AND SOMEWHAT RIGHTLY SO; THAT WE WERE ON IT; AND WE HAD TO MAKE A NUMBER OF XMISSIONS BACK AND FORTH TO MAKE SURE OF WHAT THE CTLR WANTED. THIS WAS A LOT OF STRESS AND DISTR IN A TIGHT SITUATION.