TKOF ABORTED AFTER TKOF WARNING ALERTS CREW OF PARKING BRAKE BEING IN THE 'SET' POS DURING TKOF.

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ACFT WAS FOREIGN MLG WITH ADVANCED 'GLASS' COCKPIT. ALL PREFLT AND BEFORE TKOF CHKS PERFORMED IN ACCORDANCE WITH ACR AND FAA APPROVED CHKLISTS INCLUDING TKOF CONFIGN CHK WHICH INVOLVES PRESSING A BUTTON WHICH YIELDS A 'TKOF CONFIGN NORMAL' MESSAGE ON MFDS IF ALL PARAMETERS INVOLVING A VALID TKOF CONFIGN ARE MET. THIS SYS IS DESIGNED TO ALLOW A 'NORMAL' MESSAGE EVEN WHEN THE ACFT PARKING BRAKE IS SET BUT WILL PRODUCE A RED FLASHING; 3 CHIME WARNING PLUS A 'TKOF CONFIGN PARK BRAKE' MESSAGE ON MFDS IF THRUST IS ADVANCED TO MIN TKOF PWR SETTING WITH PARKING BRAKE SET. WITH ABOVE IN MIND; HERE'S WHAT HAPPENED: TWR CLRED OUR FLT FOR TKOF; FO ADVANCED THRUST LEVERS AS ACFT BEGAN TKOF ROLL. ACFT ACCELERATED NORMALLY BUT AS PWR REACHED MIN TKOF SETTING WE GOT A PARK BRAKE TKOF CONFIGN WARNING. PWR WAS BROUGHT BACK TO IDLE; ATC WAS INFORMED WE WOULD EXIT RWY. ACFT SPD WAS AT ABOUT TAXI SPD. PARK BRAKE 'T' HANDLE APPEARED TO BE IN THE FULL DOWN OR 'OFF' POS; HOWEVER; ONCE CLR OF RWY NOTICED THAT FREE END (EXCESS) OF CAPT'S R LAP BELT (FASTENED) HAD BEEN TRAPPED BTWN CONSOLE AND BOTTOM OF PARK BRAKE 'T' HANDLE PREVENTING IT FROM GOING ALL THE WAY FLUSH AND DOWN THUS CAUSING BRAKES TO BE OFF BUT ANNUNCIATED 'ON' BY TKOF WARNING. REMOVING LAP BELT 'CURED' THE PROBLEM AND SUCCESSFUL TKOF FOLLOWED. DISPATCH INFORMED US THAT FAA WAS INVOLVED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CALLED BACK AND STATED THAT A RPT OF THIS INCIDENT WAS SENT TO HIS ACR DISPATCH OFFICE. DISPATCHER HAD NOTIFIED RPTR THAT THE FAA WAS LOOKING INTO THE ABORT TKOF SINCE A RETURN TO THE RAMP HAD NOT BEEN EXECUTED AFTER THE ABORT. RPTR FELT THAT THIS WAS NOT A 'STRAIGHT MECHANICAL PROBLEM' AND DID NOT REQUIRE A LOGBOOK ENTRY. RPT WAS FILED AS A PRECAUTION AGAINST ANY VIOLATION. RPTR HAD NOTHING ELSE TO ADD OF SUBSTANCE. RPTR AGREED THAT SENSING OF WARNING SYS COMES OFF OF 'T' HANDLE POS RATHER THAN BRAKE SENSORS.