A FAIRCHILD SA-227 ON TKOF AT 95 KNOTS VEERED L AT A HIGH RATE OF SPEED. TKOF REJECTED. INCURRED RWY EXCURSION AT 100 KNOTS.

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ON 2003/05/WED AT APPROX XA:55 THE FAIRCHILD SA-227 AC I WAS PILOTING EXPERIENCED AN UNCOMMANDED LOSS OF DIRECTIONAL CTL. THIS OCCURRED DURING THE TKOF ROLL FROM RWY 31 AT ZZZ; US. IN MY PREVIOUS OP OF THE NOSEWHEEL STEERING (NWS) CTL SYS THERE WAS NO INDICATION OF AN IMMINENT MALFUNCTION. THE TKOF ROLL WAS NORMAL UNTIL ACCELERATING THROUGH APPROX 95 KIAS. PREVIOUS TO THIS; HAVING ALREADY ENSURED BOTH ENGINES WERE PRODUCING 'POSITIVE TORQUE;' AND UPON ACCELERATING THROUGH 40 KIAS; THE NWS BUTTON ON THE L POWER LEVER WAS RELEASED THEREBY DISENGAGING THE NWS CTL SYS. THE RUDDER WAS AERODYNAMICALLY EFFECTIVE AND DIRECTIONAL CTL WAS ESTABLISHED. THE NWS CTL SYS WAS SUBSEQUENTLY DISARMED. AT THIS POINT; ALL INDICATIONS WERE NORMAL AND TKOF POWER HAD BEEN SET. THE AIRPLANE ACCELERATED NORMALLY. IMMEDIATELY PRIOR TO ROTATION; PASSING THROUGH APPROX 95 KIAS; THE AIRPLANE BEGAN TO VEER LEFT OF CENTERLINE AT AN INCREASING RATE. THE TKOF WAS ABORTED WHILE TRYING TO MAINTAIN DIRECTIONAL CTL. THIS REQUIRED THE SIMULTANEOUS APPLICATION OF MAXIMUM AVAILABLE BRAKING AND RIGHT RUDDER WHILE REDUCING POWER. THE INTENT WAS TO APPLY FULL REVERSE ON BOTH ENGINES. THE SIT; HOWEVER; CONTINUED TO DETERIORATE AS RAPIDLY AS THE LIKELIHOOD OF MY REMAINING ON THE RWY. ACCORDINGLY; MAXIMUM DIFFERENTIAL POWER WAS APPLIED. THIS WAS ACCOMPLISHED WITH EACH HAND ON THEIR RESPECTIVE POWER LEVERS; WITH THE L APPLYING FULL POWER AND THE R CONTINUING TO APPLY FULL REVERSE. THE AIRPLANE PROCEEDED TO EXIT THE L SIDE OF THE RWY AT APPROX 95-100 KIAS. IT CONTINUED TO TRAVEL ALONG A GRASSY; UNOBSTRUCTED PATH IN A PROGRESSIVELY WESTWARD DIRECTION. WHILE IT DID SO; AN ATTEMPT WAS MADE TO APPLY REVERSE THRUST TO BOTH ENGS. THE RESULT WAS AN AGGRESSIVE 'PITCHING FORWARD' AND 'LEFT YAWING' TENDENCY. IN AN ORDER TO AVOID THIS; ADEQUATE DIFFERENTIAL POWER WAS MAINTAINED. THE AIRPLANE INTERSECTED TXWY 'C3' AT APPROX A 45 DEG ANGLE. FULL REVERSE HAD BEEN APPLIED TO BOTH ENGS IMMEDIATELY PRIOR TO CONTACTING THE HARD SURFACE. THE AIRPLANE; AFTER PASSING THROUGH THE TXWY LIGHTS OF 'C3;' ABRUPTLY REVERSED COURSE TO THE L; AND ONCE AGAIN PASSED THROUGH THE SAME LIGHTS HAVING TURNED IN EXCESS OF 180 DEGS. CONTINUING TO APPLY FULL REVERSE; THE AIRPLANE'S L PROPELLER STOPPED SHORT OF CONTACTING THE TXWY 'C' SIGN. NO DAMAGE TO ARPT PROPERTY; OFFICIALLY AN INCIDENT--MECHANICAL FAILURE OF NOSEWHEEL STEERING. WAS REPLICATED BY MAINT/SENIOR LINE PLT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE NOSE STEERING WAS FULLY DISCONNECTED PASSING THROUGH 40 KNOTS AND THE RUDDER WAS CTLING THE AIRPLANE DOWN THE CENTERLINE. THE RPTR SAID AT 95 KNOTS THE AIRPLANE VEERED TO THE LEFT AT HIGH SPEED AND EXITED THE RWY. THE RPTR STATED THE TKOF WAS REJECTED AND DIRECTIONAL CTL WAS LOST AS THE AIRPLANE CROSSED THE GRASS AND A TXWY TWICE AND FINALLY WITH A COMBINATION OF ENG REVERSE AND BRAKING GOT THE AIRPLANE CTLED AND STOPPED. THE RPTR SAID THERE WAS NO DAMAGE TO THE ACFT OR THE ARPT FACILITIES. THE RPTR STATED MAINT FOUND A NOSE STEERING SERVO VALVE HAD FAILED.