3 PERSON FLC OF AN LGT CONDUCTED A FLT KNOWING THAT THE SPD BRAKE DEPLOYED WARNING SYS WAS NOT WORKING.

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ON TAXI TO THE ACTIVE RWY AT O'HARE THE COCKPIT CREW WAS COMPLETING THE COMPANY APPROVED TAXI CHKLIST. WE CAME TO THE ITEM SPDBRAKE WARNING. THIS ITEM IS TO CHK TO MAKE SURE IF THE ACFT IS NOT CONFIGURED PROPERLY; YOU WILL GET A TKOF WARNING HORN. THE CAPT MOVES THE SPDBRAKE LEVER OUT OF THE STOWED POS TO SIMULATE A MISCONFIGN AND THE FO MOVES THE SAFETY BYPASS SWITCH IN ORDER TO BYPASS THE THROTTLE SWITCH. THE HORN SHOULD SOUND AT THIS TIME. THEN THE CAPT MOVES THE SPD BRAKE LEVER TO THE STOWED POS AND THE HORN SHOULD SILENCE. WHEN THE CAPT MOVED THE SPDBRAKE LEVER OUT OF THE STOWED POS; NO WARNING HORN SOUNDED. THE CREW TRIED SEVERAL TIMES TO GET A HORN; DOUBLE-CHKING THE PROPER PROCS. THE FE CHKED ALL THE CIRCUIT BREAKERS WERE IN. THE CAPT AND FO CHKED AND RECHKED TO MAKE SURE THE ACFT WAS CONFIGURED PROPERLY. THE CREW CONTINUED THE FLT TO DEST UNEVENTFULLY. UPON LNDG THE CREW CHKED THE MEL AND FOUND THIS ITEM WAS NOT LISTED. A WRITE-UP WAS PUT IN THE BOOK AND DISCOVERED THIS WAS A SAFETY OF FLT ITEM. CONTRIBUTING FACTORS WAS THAT WE COULD NOT LOCATE THE FE EARLIER IN THE DAY. THIS MADE US LATE FOR TKOF. ALSO TWR WAS RUSHING US TO TAKE THE ACTIVE RWY DUE TO SHORT TAXI. WE WERE RUSHING THE CHKLIST; ALTHOUGH WE COMPLETED ALL ITEMS; I FEEL THESE FACTORS LED ME TO ACCEPT AN ACFT FOR TKOF WHEN IT SHOULD NOT HAVE GONE UNTIL FIXED. IN THIS SIT WE SHOULD HAVE TAXIED TO A REMOTE LOCATION AND TRIED TO FIX THE PROB. IF WE COULD NOT FIX IT THEN TAXI BACK TO THE HARD STAND AREA AND GET MAINT SUPPORT. ANOTHER CONTRIBUTING FACTOR WAS OUR FUEL STATE. WE HAD JUST ENOUGH FUEL FOR THE FLT. I DID NOT WANT TO TAKE A DELAY OR WE WOULD HAVE HAD A FUELING DELAY.