ACR MD80 FLC DSNDED FROM THEIR ASSIGNED ALT BEFORE THEY WERE CLRED FOR THE APCH. THE CTLR WAS WAITING FOR THE FLC TO CALL VISUAL CONTACT WITH ANOTHER ACFT BEFORE ASSIGNING APCH CLRNC. WHEN THE GS INTERCEPT WAS INDICATED THE CAPT FALSELY ASSUMED THAT THE FLT WAS CLRED FOR THE APCH.

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FLT WAS INBOUND FROM PHX TO DFW. ON THE LOC TO RWY 13R AT 4000 FT AND 210 KIAS; WE WERE CLRED TO INTERCEPT THE LOC ABOUT 15 MI OUT AND THE CAPT ARMED THE LOC FOR THE INTERCEPT. THE FREQ WAS VERY CONGESTED WITH RADIO TFC AS WE FLEW INBOUND TO THE FIELD. WE WERE TOLD TO SLOW TO 190 KIAS; I BELIEVE; AND AT ABOUT 9 MI WE WERE TOLD THAT WE WERE FOLLOWING COMMUTER TFC ABOUT 5 MI AHEAD AND DID WE HAVE TFC IN SIGHT? IT WAS HAZY OUT AND WE WERE FINALLY ABLE TO ACQUIRE THE TFC BUT ELECTED TO HOLD OFF ON THE CALL BECAUSE WE WERE NOT SURE WE WOULD BE ABLE TO MAINTAIN VISUAL SEPARATION TO THE FIELD. I TRIED TO VERIFY WITH THE CTLR THAT WE WERE CLRED FOR THE ILS APCH BUT WAS NOT ABLE TO GET A WORD IN. AS THE GS CAME DOWN; THE CAPT SAID HE WAS GOING TO DSND. AS HE DID; I WAS ABLE TO TALK TO THE CTLR AND SHE REPLIED NO WE WERE NOT CLRED TO DSND AND TO TURN TO A 170 DEG HDG FOR TFC. WE TOLD HER WE HAD THE TFC IN SIGHT AND SHE GAVE US CLRNC FOR THE VISUAL APCH. WE FOLLOWED THE TFC IN AND LANDED WITH NO FURTHER INCIDENT.