What was found
AIRCRAFT WAS ON APPROACH TO LAND AT FWA WHEN THE PILOT SELECTED GEAR DOWN, THEY HAD THREE GREEN & A RED LIGHT, INDICATING THAT THE GEAR WAS DOWN & LOCKED BUT THE GEAR DOORS MAY NOT BE UP. THE CREW USED THE NITROGEN TO RETRACT THE GEAR DOORS & THE LIGHT WENT OUT, THEY LANDED WITHOUT INCIDENT. THE ACFT WAS LOOKED AT & THE GEAR WAS CYCLED THRU 5 TIMES FAULT FREE. LOOKED THE GEAR OVER SERVICED THE NITROGEN & DETERMINED THEY COULD NOT DUPLICATE THE PROBLEM. CHANGED ONE LT GEAR DOOR DOWN SWITCH JUST BECAUSE IT FELT RATCHETY WHEN MOVED BY HAND, BUT WE COULD NOT DUPLICATE THE PROBLEM.