FLC UNABLE TO COMPLY WITH CLRNC.

Narrative

WHILE FLYING AT FL310 ON THE BUNTR 1 ARR AT A POINT BTWN GUP AND SLIDR; WE WERE VECTORED OFF COURSE TO THE N ON A HDG OF 275 DEGS (WHICH WAS APPROX A 62 DEG TURN). AT A POINT NEARLY ABEAM SLIDR WE WERE CLRED TO FLY DIRECT TO SLIDR TO JOIN THE BUNTR ARR. (I PRESSED THE DIRECT KEY AND LINE SELECTED SLIDR ON THE MCDU.) THE PLANE TURNED TOWARD SLIDR AND THE NAV DISPLAY SHOWED A LARGE S-TURN WITH THE ACFT WANTING TO REVERSE COURSE TO GET TO SLIDR. AS WE GOT CLOSER TO SLIDR; THE NAV DISPLAY SHOWED A TURN PRIOR TO THE INTXN (WHICH I BELIEVED TO BE NORMAL FOR THE AIRBUS). TRYING TO COMPLY WITH CTR'S CLRNC; AND AFTER ASSESSING THE REQUESTED CLRNC; I HAD CONCERN OVER THE FACT THAT MY ACFT WAS TURNING PRIOR TO SLIDE INTXN. IT BECAME APPARENT THAT MY ACFT WAS INCAPABLE OF PROCEEDING DIRECT TO SLIDR AND I WAS READY TO ADVISE CTR BUT WAS UNABLE TO DO SO DUE TO FREQ CONGESTION. SIMULTANEOUS TO THIS CONCERN; AS WE WERE JOINING THE ARR; ZAB GAVE US A FREQ CHANGE. AFTER WAITING TO CHK IN ON THE NEW FREQ DUE TO HIGH VOLUME; WE WERE GIVEN A VECTOR OF 225 DEGS S OF THE COURSE. WE CONTINUED ON VECTORS MOST OF THE WAY INTO PHX AND UPON LNDG WERE TOLD TO CALL ZAB. I SPOKE TO THE MGR OF ZAB (ON THE PHONE) WHEREIN HE ASKED WHY MY ACFT HAD NOT FLOWN DIRECTLY OVER SLIDR INTXN. AFTER REVIEWING THE CIRCUMSTANCES; IT IS MY OPINION THAT CTR SHOULD NOT HAVE PRESENTED US WITH A DIRECT CLRNC TO SLIDR DUE TO OUR ASSIGNED SPD AND POS WHICH WAS VIRTUALLY PAST THE STATED INTXN; THUS PHYSICALLY INCAPABLE OF COMPLYING WITH THE CLRNC AS REQUESTED. AT THE POINT THAT I BECAME AWARE OF THIS; AGAIN I WAS UNABLE TO ADVISE DUE TO THE SIMULTANEOUS FREQ CHANGE AND CONGESTION ON THE RADIO.