TKOF WITH IRS IN ALIGN.

Narrative

DURING PREFLT PREPARATIONS; THE IRS'S WERE ALIGNED BY THE CAPT WHILE THE FO WAS ABSENT FROM THE COCKPIT. UPON RETURNING TO THE COCKPIT; THE FO TURNED OFF THE IRS'S IN PREPARATION FOR ALIGNMENT. NOT REALIZING THAT THEY HAD ALREADY BEEN DONE. THE CAPT WAS ABSENT FROM THE COCKPIT AT THE TIME. THE APPROPRIATE CHKLISTS WERE ACCOMPLISHED PRIOR TO PUSHBACK AND START. HOWEVER; NEITHER CREW MEMBER RESET THE NAV ON THE IRS. THE WARN FLAGS IN THE FLT INSTS APPEARED TO BE NORMAL AS IN THE ADJUSTMENT PERIOD AND DIDN'T APPEAR OUT OF THE ORDINARY. SINCE THE IRS'S HAD ALREADY ALIGNED; NO ABNORMAL INDICATIONS WERE NOTED IN THE FMC OR THE IRS PANEL. THE BEFORE TKOF CHKLIST WAS DONE SHORTLY AFTER TAXI BEGAN TO THE ACTIVE RWY. WHILE FLT INSTS ARE NOT SPECIFICALLY INCORPORATED INTO THESE CHKS; THE WARNING FLAGS AND ERRONEOUS HDG INDICATION SHOULD HAVE BEEN OBVIOUS. TKOF CLRNC WAS RECEIVED AND ON ROTATION THE INVALID INSTS INDICATING WERE DETECTED. FORTUNATELY THE WX WAS GOOD VFR AND THE INITIAL CLBOUT WAS ACCOMPLISHED BY THE STANDBY ATTITUDE INDICATOR FOR REF. DURING THE CLB A LEVEL OFF AT 6800 FT WAS REQUESTED TO REMAIN VFR; TO RESET THE HDG IN THE FMC. IT TOOK ABOUT 3-5 MIN TO BRING EVERYTHING BACK TO NORMAL AND CONTINUE A NORMAL DEP AND ARR AT OUR DEST. SUGGESTION -- BE MORE VIGILANT ON HDG CHK ON TAXI OUT. ALSO OUR FMC'S COULD NOT BE USED AT THE TIME BECAUSE OF AN INOP FUEL GAUGE; THIS ALSO ADDED TO THE SIT BECAUSE THE FMC'S WOULD NORMALLY FLASH A NOTE THAT IT HAD NO POS INFO.