LTT EXPERIENCES HYD PUMP FAILURE LEADING TO LOSS OF BRAKES AND STEERING ON TAXI OUT DTW.

Narrative

WHILE TAXIING FOR DEP TO RWY 3C ON TXWY K ABEAM TXWY K15; THE HYD CAUTION LIGHT ILLUMINATED. MY FO WAS ASKED TO COMPLETE THE QRH CHKLIST. MY FO DID THE REQUIRED PROCS OUTLINED IN THE QRH. THE END OF THE QRH SECTION FOR THIS PARTICULAR FAILURE IS TO HAVE THE HYD PUMP SWITCH MOVED FROM ITS 'AUTO' POS TO THE 'OVERRIDE' POS. THIS OVERRIDE POS DIDN'T SOLVE THE PROB. KNOWING THAT POS DIDN'T SOLVE THE PROB; I IMMEDIATELY STOPPED THE ACFT. BEING IN THE CLOSE PROX TO OTHER ACFT AND GND CREW MEMBERS NEXT TO US ADJACENT TO THE TXWY THAT WE WERE ON; I HAD MY FO REQUEST TO TAXI TO A PLACE WHERE WE WOULD NOT JEOPARDIZE THE SAFETY OF OTHER ACFT AND TERMINAL STRUCTURES; SINCE THE BRAKES WORKED BUT THE PRESSURE WAS INADEQUATE TO SET THE PARKING BRAKE. ONCE WE GOT AWAY FROM THE HAZARDS AROUND US; I CONTACTED OUR MAINT OVER THE RADIO AFTER I BROUGHT THE ACFT TO A COMPLETE STOP. BOTH OF US HELD THE BRAKE AS I REQUESTED AN ACFT TOW BACK TO THE GATE. A FEW SECONDS LATER; THE ACFT STARTED TO MOVE L. I TRIED TO CORRECT THE SIT BY USING DIFFERENTIAL PWR AND REVERSE AND EVEN THE BRAKES AND NOSE STEERING TILLER; BUT BECAUSE OF THE FAILED PUMP; I HAD NO NOSE STEERING AND BRAKES. WITH AN ACFT IN FRONT OF US ABOUT 25 YARDS WAY; I HAD NO OTHER CHOICE BUT TO SHUT THE R ENG DOWN THEN THE L TO KEEP AWAY FROM THE ACFT IN FRONT OF US WHEN IT BECAME CLR THAT THE GRASS ADJACENT TO THE TXWY WE WERE ON WAS OUR ONLY OPTION. WITH THE GND SURGE BY SHUTTING DOWN THE 2 ENGS; WE ENDED UP SPDING UP TOWARDS THE GRASS AND ENDED UP THERE WITH 3 (ALL) GEARS OFF THE PAVEMENT. NO DAMAGE TO THE ACFT AND NO INJURIES WERE RPTED. THE PAX WERE ESCORTED OFF THE ACFT AND TRANSPORTED BACK TO THE TERMINAL IN A SHUTTLE BUS.