A C421 PLT; TAXIING FOR TKOF AT SGR; RESPONDED TO ANOTHER ACFT'S CLRNC AND TAXIED PAST THE HOLD SHORT LINE.

Narrative

WHILE HOLDING SHORT OF RWY 17 AT THE SUGARLAND ARPT (SGR) AWAITING AN IFR RELEASE FROM THE APCH TWR; I WAS CLRED INTO 'POS AND HOLD' BY THE SGR TWR. I REPEATED THE CLRNC BACK TO THE TWR AND PROCEEDED PAST THE HOLD SHORT LINES TO COMPLY WITH MY CLRNC. AS I STARTED TO MOVE I LOOKED TO THE N TO SEE IF FINAL WAS CLR AND THEN LOOKED TO THE S AND NOTICED ANOTHER ACFT WAS MOVING FROM ANOTHER TXWY TOWARD THE RWY FROM A HOLD SHORT POS. THIS OTHER ACFT WAS APPROX 1500 FT AWAY. I THEN IMMEDIATELY STOPPED MY ACFT BEFORE ENTERING THE RWY SURFACE AREA WHILE STILL ON THE TXWY. I THEN WAS GOING TO QUERY THE TWR AS TO WHICH ACFT WAS CLRED INTO POS. BEFORE I WAS ABLE TO ASK THE TWR; THE TWR CALLED MY ACFT AND SAID IT LOOKED LIKE I HAD PASSED THE HOLD SHORT LINES. I EXPLAINED TO THE TWR THAT I BELIEVED THAT I WAS CLRED INTO POS ON THE RWY AND HAD READ BACK MY CLRNC WITH MY TAIL NUMBER; TO COMPLY WITH THE CLRNC. APPARENTLY BOTH ACFT ENDED IN SIMILAR LETTERS AND PERHAPS BOTH ACFT MAY HAVE READ BACK THE CLRNC AT THE SAME TIME. THE TWR SEEMED BUSY WITH SEVERAL ACFT INBOUND AND ALSO LOOKING FOR 2 IFR RELEASES; MINE; AND THE ACFT BEHIND ME. SINCE THE TAIL NUMBERS WERE SIMILAR; OR THE 2 XMISSIONS OCCURRED AT THE SAME TIME; THE CTLR MIGHT HAVE NOT REALIZED THE ERROR THAT HAD OCCURRED. FORTUNATELY; WHEN I STARTED TO TAXI PAST THE HOLD SHORT LINE; I NOTICED THE OTHER ACFT'S MOVEMENT TO THE S AND STOPPED IMMEDIATELY. NO DISRUPTION OR GAR'S OCCURRED BY OTHER ACFT. THE ACFT TO THE S WAS CLRED FOR TKOF AND THEN I WAS CLRED INTO POS AND HOLD FOLLOWED BY A TKOF CLRNC. IT WAS POSSIBLE THAT I RESPONDED TO THE WRONG TAIL NUMBER; OR THE CTLR SAID THE WRONG TAIL NUMBER. EITHER WAY; WHEN TFC LEVELS ARE HIGH; BOTH PLTS AND CTLRS MUST QUERY EACH OTHER WHEN IN DOUBT TO PREVENT THIS AND SIMILAR SITS.