A SF340 FLIGHT CREW LOST HYDRAULICS DURING TAXI. THEY FOUND THEY HAD NO STEERING OR BRAKES AND HAD TO SHUT DOWN THE ENGINES TO AVOID RUNNING INTO OTHER AIRCRAFT OR EQUIPMENT.

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ON TAXI; HYD CWP ILLUMINATED. MEMORY ITEMS WERE COMPLETED BY THE FO. QRH; NON-NORMAL CHKLISTS WERE COMPLETED BY THE FO. ASKED ATC TO STOP AND REMAIN ON TXWY AND WAS ADVISED TAXI AHEAD. THE ACFT WAS STOPPED AND ALL HYD INDICATIONS WERE NORMAL AT THAT POINT. I CONTACTED DISPATCH TO ADVISE THEM OF THE SITUATION AND THEN CONTACTED MAINT. I TALKED TO MAINT CTL AND ADVISING OF THE SITUATION AND DETERMINING THE SAFEST ACTIONS. WHILE STILL ON FREQ WITH MAINT CTL THE FO APPARENTLY WAS GIVEN INSTRUCTIONS BY GND TO MAKE A 180 DEG TO RETURN TO THE GATE. AT THIS POINT THE HYD QUANTITY WAS NORMAL AND THE MAIN; OUTBOARD; INBOARD ACCUMULATORS WERE DEPLETED. BEFORE DISCUSSING THIS FURTHER WITH GND THAT WE DID NOT TAXI AND NOT BE THE BEST PROC TO FOLLOW; THE ACFT STARTED TO VEER TO THE L. THERE WERE NOW NO BRAKES AND NOSEWHEEL STEERING AND REVERSE DID NOT PROVE TO WORK SUFFICIENTLY. I TOLD THE FO WE HAD NO BRAKES AND STARTED TO VEER OFF THE TXWY AND INTO THE GATE AREA BTWN XY AND XZ. THINKING WE MAY BE APCHING AN ACFT WING AND OR BAG CARTS I SHUT THE ENGS DOWN. THE ACFT STOPPED AND JERKED BACKWARDS. THE FO QUICKLY NOTIFIED ATC OF THE SITUATION. ONCE I ADVISED RAMP TO CHOCK US I ORDERED CFR AND CONTACTED OPS AND GND. AFTER DISCUSSIONS WITH OPS; GND AND THE FIRE RESCUE WE DECIDED THE SAFEST ACTION WAS TO BE TO COORDINATE WITH COMPANY MAINT AND GND TO DEPLANE PAX AND MAINT TOWED THE ACFT BACK TO THE GATE. ACCORDING TO MAINT CTL; THE ENTIRE HYD PUMP FAILED AT SOME POINT. AT THE TIME THEY WERE NOT SURE WHAT HAD CAUSED IT. THE GND PERSONNEL NOTED HYD FLUID ON THE GND. SUPPLEMENTAL INFO FROM ACN 810264: THE ACFT STARTED TO ROLL FORWARD AND VEER TO THE L. WE WERE ADJACENT TO GATES XX AND XY. WE IMMEDIATELY REALIZED THAT WE HAD LOST ALL HYD PWR AND WERE UNABLE TO STOP OR MAINTAIN DIRECTIONAL CTL. BOTH ENGS WERE THEN SHUT DOWN AND WE ROLLED TO A STOP 90 DEGS L FROM OUR ORIGINAL POS; FACING THE X CONCOURSE BTWN GATES XX AND XY. AFTER WE STOPPED WE ROLLED BACKWARDS FOR A SHORT DISTANCE (APPROX 5-10 FT). NO CHANGES IN HYD GAUGE INDICATIONS WERE NOTICED WITH THE EXCEPTION THAT THE INBOARD/OUTBOARD PRESSURE READINGS WERE NIL. AFTER THE EVENT; MAINT CTL CAME ON BOARD AND RAN THE HYD PUMP AND THE PUMP AUDIBLY WAS NOT SOUNDING NORMAL. INITIAL THOUGHTS WERE THAT THE HYD PUMP BURNED OUT. GND PERSONNEL STATED THAT THEY NOTICED WHAT APPEARED TO BE HYD FLUID BEHIND THE ACFT.