CAPT OF A B737 TAXIED PAST THE RWY HOLD SHORT LINE AND WAS DIRECTED TO MAKE A 180 DEG TURN AROUND BY TWR IN ORDER TO PROPERLY CLR THE RWY AREA.

Narrative

AFTER RECEIVING TAXI CLRNC FROM GATE AT BWI TO RWY 28; TAXI COMMENCED AND TKOF CHKLIST ITEMS WERE BEING COMPLETED. I LOOKED AND QUESTIONED THE CAPT ABOUT CLRNC TO RWY 28 WHICH HE CONFIRMED AND I THEN QUESTIONED IF WE WERE NOT ABOUT TO INCUR ON RWY 28. HE ANSWERED THAT WE WERE NOT ABOUT TO INCUR AND THEN STOPPED ABRUPTLY. APPARENTLY MY QUESTIONING SET OFF ALARMS IN HIS HEAD AND HE IN FACT REALIZED THAT WE WERE ABOUT TO CROSS RWY 28 HOLD SHORT LINES. THE NOSE OF THE ACFT WAS IN FACT OVER THE HOLD SHORT LINE BUT NO CONFLICT OCCURRED WITH AN ACFT IN POS AT THE END OF THE RWY. THE TWR THEN INFORMED US OF THE 'INCURSION' AND ISSUED US A 180 DEG TURN BACK ONTO THE MAIN TXWY. THE CAPT WAS TOTALLY AMAZED AND APOLOGIZED TO ME MANY TIMES FOR HAVING COMMITTED SUCH A STUPID MISTAKE. COMPANY 'READ BEFORE FLT' BOOKS HAD COVERED THIS EXACT SCENARIO; AND THE CAPT NOW STATED THAT MAYBE THOSE WHO HAD COMMITTED THIS ERROR PREVIOUSLY WEREN'T DUMB; BUT JUST HUMAN. IN HIS OWN MIND THIS INCIDENT WAS BROUGHT ABOUT BY BEING OVERLY FAMILIAR WITH THE AIRFIELD AND BEING LULLED INTO A FALSE SENSE OF SECURITY.