RWY EXCURSION AFTER TKOF ABORTED DUE TO ACFT CONFIGN PROB SENSED BY WARNING SYS.

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FLT WAS BOUND FOR DFW FROM TXK. THE FLT DEPARTED THE GATE AT APPROX XA50 AND HAD BEEN CLRED TO RWY 22. DURING THE TAXI; THE TAXI CHKLIST WAS COMPLETED AND THE ACFT WAS HOLDING SHORT AT RWY 22. UPON RECEIVING TKOF CLRNC; THE BEFORE TKOF CHKLIST ITEMS WERE COMPLETED AND THE CAPT CALLED FOR THE PWR TO BE SET. AFTER SETTING AND CONFIRMING THAT THE PWR WAS SET; I MADE THE 80 KT CALL; AT WHICH TIME THE CAPT RESPONDED 'MY ACFT' AND I CONFIRMED HIS ACFT. AS WE APCHED 100 KTS; THE RED CONFIGN LIGHT AND HORN BOTH CAME ON; I CALLED FOR AN ABORT. THE CAPT WRESTLED WITH THE CTLS AND APPLIED MAX BRAKING AS WE CONTINUED DOWN THE RWY; EVENTUALLY RUNNING OFF THE END AND STOPPING APPROX 20 YARDS INTO A GRASS FIELD. ALTHOUGH THE NTSB INVESTIGATION IS NOT COMPLETE; BRAKE FAILURE AND THE PWR CONSOLE MECHANISM ARE THE PROBABLE CAUSES FOR THE INABILITY OF THE CREW TO STOP THE ACFT ON THE RWY. FACTORS CONTRIBUTING TO THE INCIDENT ARE WARM TEMP AND HIGH HUMIDITY; WT OF THE ACFT ALL REQUIRING HIGH V SPDS. THE DESIGN AND MECHS OF THE PWR LEVER CONSOLE AND THE BRAKE FAILURE ALSO CONTRIBUTED TO THE INCIDENT; AS WELL AS THE CONDITION LEVER MECHS. DETAILED TRAINING ON THE USE OF AND PECULIARITIES OF THE PWR LEVER CONSOLE AND USE OF FRICTION LOCKS SHOULD BE ADDRESSED BY THE MANUFACTURER AND THE AIRLINE IN ORDER TO PREVENT ADDITIONAL INCIDENTS.