Small Aircraft; Low Wing; 1 Eng; Retractable Gear
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 50; Flight Crew Total 15500; Flight Crew Type 500
Troubleshooting; Workload; Time Pressure
Aircraft Equipment Problem Critical; Ground Excursion Runway
Flight Crew Took Evasive Action
Aircraft
I made a visual approach to Runway XX after completing a before landing checklist.An anti-skid check was performed as part of this checklist.I then landed on Runway XX which was dry and the wind was a light and variable. The approach was made at Vref +10 and touchdown was at vref within the touchdown zone.  Air-brake was deployed as well as the thrust reverser. As I applied my initial brakes the airplane slowed; but seemed to drift left.  I released brakes applied right rudder and continued the roll out and the aircraft straightened output still left of center. The aircraft continued to decelerate using reverse and nose wheel steering.  Slowing below 80 knots additional braking was used slow to a taxi speed. The airplane pulled left with additional braking and steering applied and the nose gear and left main tires went into the grass just to the left side of the runway at the speed of a fast walk and then came to a stop with approximately 1;500 feet of runway remaining just prior to the taxiway.  The right main gear remained well on the runway. There was no damage to the aircraft; airport surfaces; or airport signage. The aircraft was shutdown and passengers were deplaned and the runway was closed until the aircraft was towed back to the hangar. The crew had normal brake pressures and quantity indications and no reason to suspect a loss of fluid or braking ability. The co-pilot assisted in applying right rudder and his brakes at the slow end of the roll out. Maintenance has since found after further inspection a broken/damaged right proximity switch.  This would have the effect of leaving that switch in the air mode configuration on the right gear and braking only available to the left main wheels. The damaged switch will now be replaced.
Corporate Pilot reported that during the landing roll out as brakes were applied the aircraft began to yaw to the left; resulting in a runway excursion. Maintenance determined the right main gear squat switch had failed resulting in no brakes on the right main.