As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED GEAR DISAGREE MASTER WARNING ON GEAR RETRACTION AFTER TAKEOFF FROM TYS. LEFT MAIN GEAR INDICATED RED. CREW RAN QRH, PERFORMED MANUAL GEAR EXTENSION, RETURNED TO TYS AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE TROUBLESHOT, REMOVED AND REPLACED PSEU (PROXIMITY SENSOR ELECTRONIC UNIT) AND PERFORMED CHECKS USING AIRCRAFT MAINTENANCE MANUALS. AIRCRAFT RELEASED FOR SERVICE.