As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LANDING GEAR WILL NOT RETRACT AFTER TAKEOFF ( RED GEAR UNLOCK LIGHT REMAIN ON) FOLLOWED WITH QRH PROBLEM REMAINED. RETURNED BACK TO RBD AIRPORT SAFELY.//////DISCOVERED LH MAIN LANDING GEAR ACTUATOR JAM NUT TO BE LOOSE PERFORMED ROD ENG ADJUSTMENT AND SECURED JAM NUT