As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENROUTE FROM BFI TO PDX, THE LANDING GEAR UNSAFE LIGHT ILLUMINATED DURING THE LANDING UPLATCH CHECK. THE FIIGHT CREW CYCLED THE LANDING GEAR TO EXTINGUISH THE WARNING INDICATION. THE FLIGHT CONTINUED TO PDX FOR AN UNEVENTFUL LANDING. MAINTENANCE INSPECTED THE AIRCRAFT WHICH REVEALED THE LEFT MAIN GEAR UPLATCH CYLINDER DEFECTIVE. MAINTENANCE REPLACED THE UPLATCH CYLINDER IN ACCORDANCE WITH THE MAINTENANCE MANUAL AND PERFORMED A SUCCESSFUL OPERATIONAL CHECK. THE AIRCRAFT WAS RETURNED TO SERVICE.