FLC OF MLG ATTEMPTING PUSHBACK FROM GATE IS INTERRUPTED DUE TO NO TUG DRIVER AFTER CLRNC TO PUSH. WHEN VEHICLE DRIVER ARRIVED THE PUSHBACK CALLOUTS WERE NOT RE- ORIGINATED. DRIVER BEGAN PUSHING AND TOWBAR WHICH HAD BEEN MODIFIED BROKE AND DAMAGED THE NOSE GEAR DOOR.

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IN PUSHBACK FROM GATE; PROCS WERE INTERRUPTED BY LACK OF GND/RAMP PERSONNEL AFTER CLRNC TO PUSH. UPON ARR; TUG BEGAN PUSH WITHOUT RE-ORIGINATING PUSHBACK CALLOUTS. TOW BACK HAD BEEN MODIFIED; PRECLUDING THE 2-PIN SHEAR; TO PROTECT BOTH PLANE AND PERSONNEL. WITH BRAKES SET AND NO MOVEMENT EVIDENT; TUG DRIVER CONTINUED THE PUSH WITH ADDED PWR AND TOWBAR SNAPPED UPWARD (NOT TO THE SIDE AS DESIGNED) AND DAMAGED THE NOSE GEAR DOORS. FLT WAS CANCELED. 1) INTERRUPTED PROCS. 2) MODIFIED TOWBAR. SUPPLEMENTAL INFO FROM ACN 385380: THE MECH ADVISED US WE DID NOT HAVE A TUG DRIVER. AS I WAS ABOUT TO CANCEL OUR PUSHBACK REQUEST THE TUG DRIVER ARRIVED AND ATTEMPTED TO PUSH BACK. TOWBAR HAD AN UNAUTH MODIFICATION WHICH CAUSED IT TO RELEASE UP AND DAMAGE THE ACFT RATHER THAN THE SIDE AS DESIGNED. EXCESSIVE TUG PWR WAS APPLIED WHEN IT BECAME APPARENT THAT THE ACFT WAS NOT MOVING. CORRECTIVE ACTION: ADVISE MECH IF BRAKES ARE REPARKED. USE ONLY STANDARD TOWBARS. REVIEW 'CRITICAL ITEMS' IMMEDIATELY PRIOR TO CLEARING GND CREW TO PUSH BACK.