UNAUTH LNDG. ACR LANDS WITHOUT A CLRNC.

Narrative

I WAS THE PF. THE CAPT WAS PERFORMING PNF DUTIES. WE WERE APCHING NOV NDB ON APCH CTL AT 4000 FT FOR THE ILS RWY 35R (VISUAL CONDITIONS). APCH SWITCHED US OVER TO TWR. TWR ASKED US TO RPT NOV (APCH HAD ALREADY CLRED US FOR THE APCH). THE CAPT RPTED NOV. THE APCH WAS STABILIZED ON GS AND LOC. I CALLED FOR GEAR AND FLAPS ON SCHEDULE. APCHING 1000 FT AGL; I MADE THE SOP CALL AND THE CAPT AND MYSELF THOUGHT WE HAD BEEN CLRED TO LAND. AFTER A SMOOTH NON EVENTFUL LNDG; UPON EXITING THE RWY; THE TWR CALLED AND SAID WE WERE NOT CLRED TO LAND AND TO CONTACT GND. THERE WAS NOT ANY TFC CONFLICT. WE HAD BEEN ON THE PROPER FREQS AT ALL TIMES. I DID NOTICE A SMALL ACFT ON THE TXWY WAITING FOR US TO LAND. OTHER DATA: 767-300 ACFT. FLT FROM FCO (ROME) TO MXP (MILAN). ACTUAL FOR TIME: 58 MINS. NO UNUSUAL EVENTS DURING FLT. VISIBILITY WAS GOOD; WHEREAS THE TWR HAD BEEN ABLE TO SEE US ON THE APCH SEVERAL MI OUT; BUT DID NOT COMMUNICATE WITH US UNTIL ON THE GND. WE DID NOT TRY TO COMMUNICATE ANYMORE BECAUSE WE THOUGHT WE HAD BEEN CLRED TO LAND. NO OTHER TFC ON FREQ (TWR).