AN ATR-72 ROLLED INTO A GND PWR UNIT.

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UPON ARR AT ORD'S CONCOURSE; THE FLC OF ATR-72 OBTAINED CLRNC INTO THE GATE. ACR OPS ASSIGNED GATE X AS THE ARR GATE. THE FLC WAITED UNTIL APPROPRIATE GND PERSONNEL (RAMP MARSHALLER AND WING WALKER) ARRIVED TO PROVIDE NECESSARY DIRECTIONS (HAND SIGNALS) FOR PARKING. THE CAPT TAXIED INTO THE GATE AREA AS DIRECTED BY GND PERSONNEL; WHILE THE FO LOOKED OUTSIDE THE ACFT; AS REQUIRED BY COMPANY OPS MANUALS. THE CAPT INITIATED A TURN TO THE R AS DIRECTED BY THE GND CREW. THE GND MARSHALLER SIGNALED FOR THE ACFT TO STOP. THE ACFT WAS STOPPED AND THE CAPT SET THE PARKING BRAKE. THE PROPS WERE FEATHERED AND THE SEAT BELT SIGN WAS TURNED OFF. THE CREW BEGAN SHUTDOWN PROCS. THE GND MARSHALLER THEN SIGNALED THAT ADDITIONAL MANEUVERING OF THE ACFT WAS REQUIRED. THE CAPT TURNED THE SEAT BELT SIGN BACK ON; AND MADE A PA TO REQUEST THAT ALL PAX RETURN TO THEIR SEATS AND FASTEN THEIR SEAT BELTS. THE CAPT VERIFIED; VIA INTERPHONE WITH THE LEAD FLT ATTENDANT; THAT ALL PAX WERE SEATED WITH THEIR SEAT BELTS FASTENED. THE PROPS WERE TAKEN OUT OF FEATHER; THE CAPT RELEASED THE PARKING BRAKE AND INITIATED A TURN TO THE R; AS DIRECTED BY THE GND CREW. THE GND MARSHALLER SIGNALED FOR THE ACFT TO STOP. THE CAPT STOPPED THE ACFT AND SET THE PARKING BRAKE AGAIN. THE PROPS WERE FEATHERED AGAIN. THE FLT PROCEEDED WITH NORMAL SHUTDOWN AND PARKING PROCS. THE FOCUS AT THIS POINT IS INSIDE THE COCKPIT; NOT OUTSIDE. THE CREW LOOKED UP AND NOTICED GND PERSONNEL WAVING TOWARD THE COCKPIT; ALTHOUGH NO EMER STOP SIGNAL WAS RECEIVED FROM GND PERSONNEL. THE ACFT HAD ROLLED FORWARD AND STRUCK A GND PWR UNIT WHICH HAD BEEN CONNECTED TO THE ACFT. THE CAPT REACHED FOR THE PARKING BRAKE HANDLE; AND SET THE PARKING BRAKE AGAIN. THE GND CREW HAD FAILED TO INSERT WHEEL CHOCKS PRIOR TO THE CONNECTION OF GND PWR. THE PARKING BRAKE HANDLE WAS IN THE FULL RELEASE POS WHEN THE CAPT GRABBED IT TO SET IT AGAIN AFTER THE ACFT ROLLED INTO THE GND PWR UNIT. THE BRAKE HANDLE IS LOCATED ON THE L SIDE OF THE CTR COCKPIT PEDESTAL; ADJACENT TO THE CAPT'S SEAT. THE CAPT IS RESPONSIBLE FOR SETTING AND RELEASING THE BRAKE IN ALL NORMAL OPS. PRIOR TO BEGINNING COMPANY PAPERWORK AFTER PARKING; THE FO IS REQUIRED TO INSURE THAT THE CAPT HAS SET THE PARKING BRAKE. THE FO IS THEN FREE TO BEGIN HIS/HER POSTFLT COCKPIT DUTIES. IN THE INCIDENT DESCRIBED ABOVE; THE CAPT HAD PROPERLY SET THE PARKING BRAKE. THE FO NEITHER FELT NOR WITNESSED THE BRAKE RELEASE. IN THIS PARTICULAR ACFT TYPE; ONCE THE PROPS ARE FEATHERED; PRIMARY HYD SYS DROP OFF LINE AND NORMAL BRAKING FUNCTIONS (TOE BRAKES) ARE LOST. THERE WAS; THEREFORE; NO WAY FOR THE FO TO APPLY BRAKES TO EITHER PREVENT OR STOP THE ACFT FROM ROLLING FORWARD. NO EXPLANATION YET EXISTS FOR THE FAILURE OF OR RELEASE OF THE PARKING BRAKE. SUPPLEMENTAL INFO FROM ACN 266857: OUR COMPANY GND PROCS ARE NOT FOLLOWED WITH ANY CONSISTENCY BY THE GND PERSONNEL. PLTS ARE FORCED TO DISRUPT THE OPS IN ORDER TO GET BASIC HAND SIGNALS FROM GND PEOPLE. ALL TOO OFTEN; GND EQUIP IS BROUGHT TO AND ATTACHED TO THE ACFT BEFORE THE CHOCKS ARE INSERTED. THE GND CREW SHOULD BE FORCED TO ACT AS IF THE CHOCKS ARE THEIR #1 PRIORITY.