SA-227 AC Metro III
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Runway
Flight Crew Regained Aircraft Control
Aircraft
This incident report is in regard to an uncommanded turn to the right on landing rollout; in the opposite direction of control inputs.The SA-227 Metroliner had a normal flight with no equipment failure indications in flight. A normal landing was performed with touchdown on center line at the 1;000 ft mark. Upon slowing below the effective rudder control the aircraft began to pull to the right with full left rudder given as speeds were set low (This should engage NWS-nosewheel steering-switch was verified on at completion of event). [As] aircraft continued to accelerate its turn towards the right; pilot pressed the NWS button on the power lever to attempt to engage [nose wheel] steering with no success. Pilot then immediately deactivated NWS via advancing speed levers forward and performing 'no nosewheel' steering procedures and techniques.After de-activating NWS (below 30kt) pilot depressed only the left brake (felt squishy so pilot pumped brake repeatedly until aircraft came to a stop); applied reverse power setting on left engine and moved the right power lever to about 1/2 travel. As the engines powered up; the aircraft continued to veer right; pilot then applied full reverse and full braking action to stop aircraft movement as soon as possible. Aircraft came to a stop with the nosewheel approximately 2-3 feet off the runway with the mains still on the pavement. Pilot elected to shut down the aircraft on the runway and call the local FBO for assistance.Still being on the runway; the First Officer was assigned to the radios in order to warn any aircraft inbound that there was a plane on the runway (lucky no arrivals occurred during this time). The plane was pushed by hand backwards onto the runway and 270 degrees onto taxiway on the west side of the runway and then towed to parking. Airport security/manager came out as aircraft was being hooked up to the tug and questioning what was going on was simply told aircraft had steering issues was shut down and is being towed to parking.There was no damage to aircraft or airport property in this event. This was a sudden mechanical failure on a normal to narrow runway for aircraft (100ft wide). All evasive and control actions possible were exhausted by PIC and aircraft stopped with nosewheel 2-3 ft off of paved surface; would have still been on runway at other airports operated to.
SA-227 Captain experienced loss of directional control on landing roll.