What was found
ON FLIGHT 3959 DURING THE APPROACH THE CREW REPORTED, PUT THE GEAR DOWN FOR LANDING , RECEIVED A RIGHT MAIN LANDING GEAR DISAGREEMENT LIGHT. AFTER EXECUTING A GO-AROUND AND DOING THE EMERGENCY CHECKLIST EVERYTHING LOOK NORMAL. THE CREW DECLARED AN EMERGENCY AND LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. INSPECTED LEFT AND RIGHT MAIN LANDING GEARS AND FOUND ALL DOWNLOCK PROXIMITY SWITCH SENSORS EXTREMELY DIRTY AND GRIMY. ALL SENSORS AND TARGETS WERE CLEANED. SUBSEQUENT OPERATIONAL TESTS OF LANDING GEAR EXTENSION/RETRACTION FUNCTION WERE SATISFACTORY WITH RETRACT AND EXTEND TIMES VERY WELL WITHIN ACCEPTABLE LIMITS AS PER CRJ MM 32-30-00. AIRCRAFT RETURNED TO SERVICE.