AN SMT CREW TAXIED TO TAKE OFF RWY AT YIP WITHOUT A CLRNC.

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MY COPLT WAS ALREADY IN THE COCKPIT. WHEN I FINISHED MY PREFLT; I SHUT THE LOAD DOOR. AS I WAS DOING SO; I COULD HEAR HIM TALKING TO GND CTL AT YIP. I HEARD HIM SAY 'CLRED TO RWY 23R.' WE RAN THE BEFORE AND START CHKLISTS. I STARTED BOTH ENGS AND STARTED MY TAXI. GND CTL ALWAYS CLRS US THE SAME WAY -- DOWN THE RAMP TO RWY 9L TO RWY 23R. AS WE APCHED RWY 23R; I TOLD MY FO TO LET THE TWR KNOW WE WERE READY FOR TKOF; AT WHICH TIME THE TWR STATED THEY DIDN'T KNOW WE HAD TAXIED YET. THEY ASKED ME TO GIVE THE TWR A CALL WHEN WE ARRIVED AT PTK. I DID AND TOLD THEM I WAS VERY SORRY; AND WHAT HAD HAPPENED. I HAD A FAIRLY NEW FO. USUALLY BEFORE I TAXI; I ASK IF IT'S CLR ON THE R AND THE FO CALLS FOR TAXI CLRNC. IT WAS MY FAULT; I ASSUMED THE FO HAD ALREADY CALLED AND WE HAD BEEN CLRED TO RWY 23R; AS I HAD HEARD HIM SAY RWY 23R; WHILE CLOSING THE DOOR. THERE WAS NO OTHER TFC MOVING ON THE GND OR LNDG WHILE WE TAXIED. THE KEY WORD IS 'ASSUME.' DON'T EVER ASSUME ANYTHING. IF YOU'RE NOT SURE; ASK QUESTIONS.