A SAAB 340A HOLDING ON A TXWY #3 FOR TKOF HAS THE MAIN HYDRAULIC PUMP FAIL AND ACFT ROLL FORWARD. USED ASYMMETRIC THRUST TO STEER OFF TXWY.

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DURING THE TAXI; I PERFORMED THE BEFORE TKOF CHKLIST THROUGH 'FLT INSTRUMENTS AND AVIONICS.' OUR SEQUENCE FOR TKOF WAS #3 FOR RWY 23. WITH THIS SEQUENCE; THE CAPT STOPPED THE ACFT JUST SHORT OF INTXN A1 ON TXWY A DUE TO 2 ACFT IN POSITION AHEAD. AS THE ACFT WAS SLOWING WE RECEIVED A MASTER CAUTION; HYDRAULIC LOOKDOWN LIGHT ON THE CENTRAL WARNING PANEL (CWP). THE CAPT RESPONDED 'IDENTIFY CANCEL.' I RESPONDED TO THE CAUTION PER POM. THE CAPT PERFORMED THE MEMORY ITEMS; WHICH WERE TO TURN THE HYDRAULIC PUMP OFF. THE CAPT AND I EXAMINED THE HYDRAULICS PANEL TO ASSESS OUR SIT. WE OBSERVED THE FOLLOWING: EMER ACCUMULATOR; APPROX 2500-2900 PSI; MAIN ACCUMULATOR; LESS THAN 2100 PSI AND DECREASING; INBOARD BRAKE ACCUMULATOR; LESS THAN 2100 PSI AND DECREASING; OUTBOARD ACCUMULATOR; LESS THAN 2100 PSI AND DECREASING; QUANTITY; APPROX 200-250 CUBIC/IN (NORMAL). AT THIS TIME THE CAPT CALLED FOR THE QRH HYDRAULICS. I ADVISED THE CAPT I WOULD LET THE ATC TWR KNOW WE WOULD NEED SOME TIME TO RESOLVE A MECHANICAL ISSUE. SIMULTANEOUSLY; THE CAPT BEGAN TO TRY AND REPLENISH HYDRAULIC PRESSURE BY SELECTING 'OVERRIDE' ON THE HYDRAULIC PUMP OP PANEL. THE CAPT'S DECISION TO DO THIS WAS DUE TO OUR CURRENT GEOGRAPHICAL AND MECHANICAL STATUS. THE ACFT WAS POSITIONED ON A DOWN SLOPING TXWY WITH NO RUN-OFF AT THE END; AN IMMEDIATE DROP OFF TO THE RIGHT OF THE ACFT AND DECREASING HYDRAULIC PRESS. THE CAPT STATED THAT THE HYDRAULIC PUMP WAS NOT OPERATING. THIS WAS DETERMINED BY THE ABSENCE OF VISUAL AND AUDIBLE INDICATIONS. I STATED TO CHK CIRCUIT BREAKERS ON THE HYDRAULIC CIRCUIT BREAKER PANEL AND THEN COMMENCED THE QRH CHKLIST. THE CAPT CYCLED THE CIRCUIT BREAKERS FOR THE HYDRAULIC PUMP 'AUTO' AND 'OVERRIDE' MODES. THE HYDRAULIC PUMP DID NOT OPERATE. AS THE CAPT BEGAN TO FEATHER ENG NUMBER 1; THE ACFT BROKE FREE OF STATIC POSITION. I LOOKED OUTSIDE BRIEFLY AND NOTICED THE ACFT BEGAN TO ROLL. I BROUGHT THIS TO THE CAPT'S ATTENTION BY STATING 'WE'RE ROLLING.' I CHKED THE HYDRAULIC PRESSURE PANEL AND OBSERVED 0 PSI IN THE MAIN; INBOARD; AND OUTBOARD ACCUMULATORS WITH THE EMER ACCUMULATOR STILL INDICATING NORMAL PRESSURE AND HYDRAULIC QUANTITY INDICATING NORMAL. THE CAPT STATED THAT HE COULD NOT STEER THE ACFT. THE ACFT WAS ROLLING FORWARD AND SLIGHTLY RIGHT ON TXWY A. THE CAPT ADVANCED NUMBER TWO POWER LEVER TO USE ASYMMETRIC THRUST TO STEER THE ACFT AWAY FROM THE IMPENDING DROP OFF AND BACK THROUGH THE CENTERLINE AND TO THE LEFT EDGE OF TXWY A. AS WE EXITED TXWY A; I STARTED TO SHUT DOWN THE ENGS. THE CAPT SHUT DOWN NUMBER 1 AND 2 ENGS AS WE EXITED THE TXWY. AFTER THE ACFT CAME TO A STOP WE MADE AN ASSESSMENT OF OUR CURRENT POS. I NOTIFIED ATC THAT WE HAD EXITED THE TXWY AND WERE STOPPED IN BTWN THE TXWY AND RWY. THE CAPT NOTIFIED COMPANY OPERATIONS; DISPATCH; CHIEF PLT AND INSTRUCTED ME TO ADDRESS THE PASSENGERS AND FIND OUT IF MEDICAL ASSISTANCE WAS NEEDED. MEDICAL ASSISTANCE WAS NOT NEEDED. THE CAPT INSTRUCTED THAT ALL PASSENGERS REMAIN ON THE ACFT. APPROX 1 HR HAD PASSED BEFORE WE WERE ABLE TO LOCATE A TOW BAR THAT WOULD SUFFICE. THIS WAS ACR Y TOW BAR. THE MIL USED THEIR TUG ALONG WITH ACR Y TOW BAR TO TOW THE ACFT BACK TO THE RAMP. PRECAUTIONS WERE TAKEN TO ENSURE SAFE TOWING. THE ACFT WAS PARKED AND SECURED ON THE COMPANY RAMP. THE CAPT NOTIFIED DISPATCH AND MAINT CTL TO ADVISE THEM OF THE STATUS OF THE SIT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE HAS ONLY ONE SOURCE OF MAIN HYDRAULICS; AN ELECTRIC MOTOR PUMP OPERATING IN TWO MODES; 'AUTO' AND 'OVERRIDE.' THE RPTR SAID THE HYDRAULIC PUMP MOTOR SHORTED OUT; OPENING THE 800 AMP CURRENT LIMITER AND CAUSING THE LOSS OF HYDRAULIC PRESSURE. THE RPTR STATED THE ONLY HYDRAULIC BACKUP IS A HAND OPERATED PUMP WITH LIMITED CAPACITY. THE RPTR SAID THE MOTOR PUMP WAS REPLACED AND THE MAIN HYDRAULIC SYS CHKED OK.