A TOW BAR BREAKS DURING PUSHBACK.

Narrative

WITH THE APU INOP WE STARTED THE L ENG AT THE GATE. THE GND PWR EQUIP WAS DISCONNECTED AND THE PUSHBACK STARTED. WHILE BEING PUSHED BACK ON A STRAIGHT LONG SECTION; WE WERE CLRED TO START THE R ENG. BOTH ENGS WERE NOW ON LINE AND THE THROTTLES AT GND IDLE. THE TUG DRIVER PUSHED THE ACFT BACK AND TURNED US 90 DEGS FROM THE TUG. THE ACFT STARTED TO MOVE FORWARD SLOWLY WHEN THE FO NOTICED THE WING WALKER WAS ON HIS SIDE CLOSE IN SHOWING THE BRAKE SET SIGNAL. HE CALLED OUT 'SET BRAKES' AND BRAKES WERE SET. BTWN THE TIME THE ACFT WAS STARTING TO MOVE FORWARD AND BRAKES SET THERE WAS A 1-2 SECOND MIKE KEY FROM THE TUG WITH NO VOICE XMISSION. AFTER BRAKE SET; THE TUG DRIVER SAID THE TOW BAR HAD COME OFF AND THEN SAID IT BROKE. I ASKED IF EVERYONE WAS ALRIGHT AND IF THERE WAS ANY DAMAGE. IT WAS RPTED THAT THERE WAS NO DAMAGE AND ALL WAS ALL OK. THE TUG DRIVER THEN SAID THAT THE SUPVR WANTED TO SEE IF WE WANTED A MECH TO CHK FOR DAMAGE. WE SAID YES; AND A MECH CHKED US OVER AND SAID THERE WAS NO DAMAGE. AFTER AIRBORNE; WE CONTACTED DISPATCH TO RELAY THE INCIDENT. A MECH WOULD MEET US AT DEST AND WE COULD DEBRIEF HIM.