UNAUTHORIZED RWY ENTRY BY ACR CAUSED GAR.

Narrative

OUR FLT WAS CLRED BY TWR TO CROSS RWY 15 AND HOLD SHORT RWY 18. MLG ACR Z WAS HOLDING IN PAD AREA. CAPT WAS TAXIING AND I WAS ON RADIO. I TOLD TWR THAT WE WOULD BE READY AT THE END. TWR ADVISED THAT WE WOULD BE #1; HOLD SHORT. I ACKNOWLEDGED AND TOLD CAPT THAT I WOULD BE OFF TO BRIEF THE PAX ABOUT FLT. THIS LETS THE CAPT KNOW HE IS RESPONSIBLE FOR RADIO COM. (WHEN EITHER MIKE IS KEYED; ALL SPEAKERS ARE CUT OUT TO ELIMINATE FEEDBACK). WHILE BRIEFING PAX THE CAPT CONTINUED TO TAXI OVER HOLD LINE. SINCE I COULD NOT HEAR TWR WHILE TALKING TO PAX I ASSUMED WE HAD BEEN CLRED TO GO AND TOLD THE PAX JUST THAT. WHEN I CAME BACK TO TWR FREQ; TWR ASKED IF WE WERE HOLDING SHORT. BY THIS TIME THE R WING AND NOSE WERE OVER THE HOLD LINE AND WE TOLD TWR ABOUT OUR POS. TWR SAID TURN OFF RWY AND HOLD SHORT. WE HAD NOT ENOUGH ROOM TO TURN OFF THE RWY FOR LNDG TFC. TWR INSTRUCTED LNDG TFC TO GAR. WE APOLOGIZED AND TWR THEN CLRED US TO GO. CAPT MISUNDERSTOOD HOLD SHORT. HE HEARD ONLY YOU ARE #1 AND ASSUMED WE WERE CLRED INTO POS. SUPPLEMENTAL INFO FROM ACN 200662: WAS TOLD TO TAXI UP TO AND HOLD SHORT OF RWY 18. AS WE APCHED THE RWY HOLD SHORT LINE; THE FO MADE PA TO FLT ATTENDANTS 'WE HAVE BEEN CLRED ONTO RWY FOR TKOF; PLEASE BE SEATED.' I OVERHEARD THE CLRED ONTO RWY AND MISTAKENLY THOUGHT FO WAS RESPONDING TO A TWR XMISSION. AS WE CROSSED THE LINE; TWR ASKED OUR POS AND WE STOPPED AND ACKNOWLEDGED WE HAD CROSSED WHITE LINE (BY 10 FT). SINCE WE WERE UNABLE TO TURN AROUND IT CAUSED A GAR FOR LGT ACR Y MAKING APCH; THE WX WAS SNOW WITH A SLIGHT ACCUMULATION. THE VISIBILITY WAS DECREASING AND I WAS CONCERNED ABOUT SPENDING TIME ON THE GND WITHOUT DEICING. THE RWY INCURSION WHICH CAUSED A SUBSEQUENT GAR WAS COMPLETELY MY FAULT. I DO BELIEVE; HOWEVER; THE LANGUAGE USED TO ADVISE FLT ATTENDANTS SHOULD BE STRUCTURED TO PREVENT A SIMILAR SITUATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR GAVE INFO REF ACFT Y TYPE; MISS DISTANCE. SAYS TOO MANY ASSUMPTIONS ON PART OF FLC. ONCE THEY GOT PAST HOLD LINE THEY COULD NOT TURN BACK OFF RWY WITHOUT GOING ENTIRELY ONTO RWY. AFTER Y WENT AROUND THEY WERE CLRED INTO TKOF POS. ACR Z ON RUNUP PAD WAS GOING TO BE DELAYED AND TWR CTLR DID NOT WANT ACR X TO GET STUCK BEHIND THAT ACFT SO HE TOLD X THEY WERE #1.