FAIRCHILD METRO III ACFT AFTER LNDG DEPARTED RWY. ACCORDING TO RPTR THERE WAS A SYS FAILURE IN THE NOSEWHEEL STEERING; BUT ON CALLBACK WAS UNSURE WHAT THE CAUSE. NTSB AND FAA INVESTIGATING. POSSIBLY CAUSED BY STRONG XWIND AND INVESTIGATION LOOKING INTO THAT.

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LNDG RWY 35R ABI; TX. LANDED THE ACFT SLOWING THE ACFT DOWN TO MAKE THE APPROPRIATE TXWY. FLYING A METROLINER III ACFT. WENT TO ENGAGE THE NOSEWHEEL STEERING BUTTON. THE ACFT VEERED TO THE L. I PUT MAX BRAKING AND MAX REVERSERS; BUT ACFT KEPT VEERING TOWARD THE SIDE OF RWY AND WE SLID OFF INTO THE GRASS. NO INJURY; NO STRUCTURAL DAMAGE. THE RESULT OF THE ACFT SWERVING WAS UNCOMMANDED HYD PRESSURE TO CHANGE THE NOSEWHEEL TO GO TO THE L. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR CONFIRMED ACFT WAS A FAIRCHILD METRO III. RPTR FO WAS FLYING AND SAYS THAT WHEN HE ENGAGED THE NOSEWHEEL STEERING BUTTON; THE ACFT VEERED SHARPLY TO THE L AND DEPARTED THE RWY. THE PROBABLE CAUSE; ACCORDING TO RPTR; WAS A FAILURE OF HYD SYS PUTTING FULL PRESSURE CAUSING THE NOSEWHEEL TO COCK TO THE L OR THE ELECTRICAL SIGNAL TO THE HYD SYS. RPTR SAYS THAT OTHER ACFT OF THE SAME MAKE/MODEL HAVE HAD SIMILAR PROBS. THE NTSB; FAA AND THE RPTR'S DIRECTOR OF FLT OPS ARE ALL INVESTIGATING. BECAUSE THERE WAS A STRONG XWIND AT THE TIME OF THE EXCURSION; THAT IS ALSO BEING INVESTIGATED AS THE CAUSE.