LTT CROSSED AN ACTIVE RWY WITHOUT CLRNC.

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DEPARTED CVG ARPT FOR SCHEDULED PAX FLT TO GSO. TKOF AND INITIAL CLB NORMAL. AT APPROX 6000 FT; A 'SVC DOOR' AURAL WARNING WAS RECEIVED. QUICKLY MADE DECISION TO RETURN TO CVG. LANDED ON E SIDE OF ARPT; RWY 18L. GATE ASSIGNMENT REQUIRED TAXI TO W SIDE OF ARPT. TURNED OFF RWY 18L AND WERE ADVISED TO CONTACT E GND ON FREQ 121.3. GND INSTRUCTED US TO 'TAXI WBOUND ON TXWY MIKE; HOLD SHORT OF DIXIE;' THEN INSTRUCTED US TO 'CONTACT W GND; FREQ 121.7.' WHICH WE THEN DID. BOTH THE CAPT AND MYSELF BELIEVE WE THEN HEARD '(CALL SIGN) ROGER -- DIXIE TO THE RAMP.' I LOOKED TO THE L AND R AND SAID 'CLR RC' THE CAPT RESPONDED 'CLR L.' THERE WAS AN ACFT HOLDING IN POS ON RWY 27. THERE WAS ALSO AN ACFT LNDG RWY 18R; AND THAT ACFT WAS PASSING THROUGH THE INTXN OF RWY 18R AND 27 AT THE SAME MOMENT WE CROSSED 27 ON THE TXWY PARALLEL TO 18R -- THUS; THERE WAS NO TFC CONFLICT. (GND ASKED US TO PHONE THE TWR HERE.) I BELIEVE THAT IN OUR HASTE TO RECTIFY OUR 'SVC DOOR' LIGHT PROB; WE MAY HAVE CROSSED RWY 27 WITHOUT PROPER CLRNC -- (ALTHOUGH AT THE TIME WE BELIEVED WE DID HAVE CLRNC). THIS HAS NOT YET BEEN DETERMINED. HOWEVER; IF THE SECOND GND CTLR HAD REITERATED THE FIRST GND CTLR'S INSTRUCTIONS TO HOLD SHORT (WHICH HE DID NOT DO) -- THIS WOULDN'T HAVE OCCURRED. SUPPLEMENTAL INFO FROM ACN 234061: UPON CONTACTING HIM WE BELIEVE HE SAID CONTINUE 'DIXIE TO THE TERMINAL.' CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR HAS NOT HEARD THE TAPES OF HIS CONTACT WITH GND CTL BUT HIS CHIEF PLT HAS AND HE SAID THAT THE CTLR WAS RIGHT AND THAT THE ACFT WAS NOT CLRED TO CROSS THE RWY.