PLT EXPERIENCED DIRECTIONAL CTL PROBS WHILE TAXIING -- AIR AMBULANCE ACFT.

Narrative

ON OCT/XA/95 AT APPROX XA00; I TAXIED A PA31P ON A PART 135 AMBULANCE FLT AT THE BLYTHE ARPT IN CALIFORNIA. THERE WERE 5 SOULS ON BOARD -- 2 FLT NURSES; A PATIENT AND HIS MOTHER AND MYSELF (THE CAPT). UPON COMPLETION OF A NORMAL START SEQUENCE OF BOTH ENGS AND THE PRE-TAXI CHKLIST; I TAXIED THE ACFT TOWARDS THE HOLD SHORT AREA AT THE APCH END OF RWY 26 AT BLYTHE. AFTER APPROX 1/2 MI OF TAXIING; HDG APPROX 080 DEGS; THE PA31P SUDDENLY SUFFERED A DIRECTIONAL CTL PROB. THE ACFT SUDDENLY CHANGED HDG OF ABOUT 10 DEGS TO THE L. I COUNTERED THE MOTION WITH R RUDDER AND R BRAKE. THE ACFT RESPONDED AND BEGAN TURNING TO THE R. UPON RETURNING TO THE TAXI CTRLINE; I APPLIED L RUDDER AND L BRAKE TO RETURN THE ACFT TO TXWY CTRLINE TRACKING. THE ACFT SURPRISINGLY CONTINUED TO TURN TO THE R; AND I THEN ATTEMPTED TO STOP THE ACFT BY APPLYING BOTH BRAKES WITH FULL L RUDDER. AT THIS POINT; THE ACFT TURNED VERY SHARPLY TO THE R AND THE ACFT STOPPED ON THE SOUTHERN EDGE OF THE TXWY FACING APPROX PERPENDICULAR TO THE RWY. THE AIRPLANE WAS DIRECTED BACK DOWN THE TXWY TOWARDS THE HOLD SHORT. A THOROUGH DIRECTIONAL CTL AND BRAKE CHK WAS COMPLETED DURING THE REMAINING TAXI WITH NO APPARENT MALFUNCTIONS. ALL ENG RUN-UP AND PRE-TKOF CHKS WERE NORMAL AND COMPLETED. A NORMAL TKOF AND FLT WAS CONDUCTED TO SAN DIEGO AT LINDBERGH FIELD. CORRECTIVE ACTION: MALFUNCTIONING BRAKES WERE THE CAUSE OF THE INCIDENT. AN INSPECTION AND PROPER ADJUSTMENT TO THE BRAKES WOULD KEEP THE PROB FROM RECURRING. ADDITIONALLY; THE THROTTLE RIGGING APPEARED TO BE OUT OF ADJUSTMENT WHICH I THINK COULD HAVE CAUSED THE INITIAL JINK TO THE L. PROPER THROTTLE RIGGING TO CREATE A MORE UNIFORM ENG RPM WOULD ALSO; IN MY BELIEF; CREATE GREATER DIRECTIONAL CTL STABILITY.