AFTER ACR MLG WAS CLRED FOR IAP ILS APCH TO RWY 21L AT DTW AND CTLR ADVISED HE WAS BEING CHANGED TO RWY 21R. ON SUBSEQUENT HDOF THE ACR WAS VECTORED FOR APCH TO 21L AS ORIGINALLY PLANNED.

Narrative

UPON HDOF TO DTW APCH WE WERE GIVEN 'ILS 21L' APCH. VECTORS AND ALTS SEEMED NORMAL FOR THE APCH. THE CTLR THEN INFORMED US WE WERE BEING SWITCHED TO '21R' LNDG AND 'ILS 21R' APCH. HE THEN IMMEDIATELY SWITCHED US TO THE NEXT CTLR. VECTORS AND ALT STILL SEEMED NORMAL. UPON BEING GIVEN THE FINAL LOC INTERCEPT HDG; THE CTLR SAID 'CLRED FOR THE APCH; MAINTAIN 5000 TO ROBBI; 170 KTS TO SCOFI CONTACT TWR 118.4 AT SCOFI.' THE FO READ BACK THE CLRNC. I IMMEDIATELY TOLD THE FO THAT THE CLRNC WAS FOR AN 'ILS 21L' APCH AND TO REQUEST CONFIRMATION OF THE APCH. UPON ASKING FOR CLARIFICATION; THE CTLR INFORMED US WE WERE ON AN 'ILS 21L' APCH AND THAT HE WAS NOT INFORMED OF US BEING SWITCHED TO '21R.' APCH AND LNDG TO 21L WAS UNEVENTFUL. AFTER TERMINATION OF THE FLT; I CALLED THE 'RADAR ROOM' AT DTW AND ASKED IF THERE WERE ANY PROBLEMS NOTED WITH OUR FLT. THE SUPVR STATED HE HAD NO KNOWLEDGE OF ANY PROBLEMS. THEREFORE; I ASSUME; THOUGH WE WERE IMC; THAT NO TFC CONFLICT EXISTED. IN MY OPINION THE PROBLEM STARTED WITH A COM BREAKDOWN BTWN CTLRS AND THE FINAL CTLR NOT SPECIFICALLY STATING THE APCH THAT WE WERE 'CLRED FOR.'