MLG CREW HAD RWY INCURSION AT CYYZ.

Narrative

FLT DEPARTED THE GATE IN HVY WET SNOW WITH VISIBILITY AT ABOUT 1 MI. WE WERE BOTH UNFAMILIAR WITH DEICING PROCS AT TORONTO; BUT AFTER COMPLETING VERY COMPLICATED PROCS; WE WERE ON OUR WAY TO RWY 23. OUR HOLDOVER TIME WAS GOING TO BE 30 MINS. TAXI RTE WAS VERY LENGTHY (DEICE PAD FOR RWY 33L; TXWY F2 TO TXWY H WITH MANY HOLD SHORTS IN BTWN). AT APCH END OF RWY 23 ON TXWY H; GND SWITCHED US TO TWR; AT WHICH TIME WE INFORMED THEM WE WERE READY TO GO. TWR TOLD US TO HOLD SHORT FOR A VEHICLE AND AN ARR. AFTER VEHICLE MOVED OUT OF THE WAY THE CAPT MOVED THE ACFT CLOSER TO RWY 23. ACFT WAS FACING N TOWARD TXWY I. CAPT SAID HE WAS GOING TO MOVE UP AND USE FULL LENGTH. AS HE BEGAN TO MOVE ACFT; TWR ASKED WHERE WE WERE GOING AND SENT ARRIVING ACFT AROUND. THERE WERE SEVERAL CONTRIBUTING FACTORS TO THIS INCIDENT: REDUCED VISIBILITY; HVY SNOW; SHORT HOLDOVER TIME; NIGHT OP; UNFAMILIAR ARPT; CREW MEMBERS WERE UNFAMILIAR WITH EACH OTHER (SECOND LEG OF DAY). HUMAN PERFORMANCE FACTORS: I MADE A BAD ASSUMPTION; WE WERE SO CLOSE TO RWY AND I NEVER CONSIDERED THE CAPT WOULD CROSS A HOLD LINE AT THIS POINT. I DID NOT DOUBLECHK WHEN HE SAID HE WAS GOING TO USE FULL LENGTH. I BELIEVE I WAS DISTR BY CALCULATING THE EXPIRATION OF OUR HOLDOVER TIME. ADDITIONALLY; IT DID NOT LOOK LIKE THERE SHOULD HAVE BEEN A HOLD LINE AT THAT POINT ON THE TXWY AS YOU CANNOT GET ANY CLOSER TO THE RWY BY CONTINUING.