DH8 CREW DID NOT FOLLOW PUBLISHED HEADING ON STAR.

Narrative

ACTING AS PNF; ON 'DADES THREE' ARR INTO TPA DSNDING TO 7000 FT. WHEN CTLR ASKED IF WE HAD BEEN CLRED TO FLY ANYTHING OTHER THAN THE DADES ARR; I CHKED WITH THE FO (WHO WAS FLYING); BECAUSE I HAD BEEN OFF THE FREQ TALKING TO THE COMPANY. THE FO SAID 'NO' WE WERE STILL ON THE DADES ARR. ATC GAVE US A VECTOR FROM OUR SW COURSE BACK TO THE SE (AND SUBSEQUENTLY TO THE S). UPON CHKING THE ARR PROC WE SAW THAT A NEW INTXN HAD BEEN ADDED TO THE PROC. FOR A 'N' LNDG; WE SHOULD HAVE TURNED TO 180 DEGS AT 'TUMPY.' OUR FMS HAD BEEN UPDATED WITH THE INTXN BUT THE ACFT HAD PROCEEDED TOWARDS THE VOR (WHICH WAS THE NEXT FIX AFTER THE INTXN); AS IT WAS DESIGNED TO DO UNLESS RE-DIRECTED BY THE CREW (FOR PURPOSES OF LNDG N). I HAD FAILED TO NOTICE THE NEW INTXN BECAUSE I WAS 'PLAYING CATCH UP' WITH THE DSCNT PROC DUE TO MY RECENT INACTIVITY IN LINE FLYING (7 DAYS OF FLYING IN THE LAST 4 MONTH PERIOD). NO EXCUSE; AND COMPLACENCY IN ASSUMING THAT THE PROC HADN'T CHANGED DURING THE PREVIOUS SEVERAL MONTHS.