What was found
MCI - FLT 301 - AIR RETURN, NO EMERGENCY DECLARED, LANDING UNEVENTFUL. AFT CARGO DOOR LIGHT CAME ON AFTER TAKEOFF, AIRCRAFT WAS NOT PRESSURIZING. RETURNED TO MCI. CHECKED AFT CARGO DOOR PROXIMITY SWITCH AND TARGET. NO DEFECTS FOUND, AFT CARGO DOOR WARNING LIGHTS OPS CHECK NORMAL. CHECKED PRESSURIZATION CONTROL SYSTEM PER MM 21-31-0, OPS CHECK NORMAL. PRESSURIZED AIRCRAFT ON GROUND, AIRCRAFT PRESSURIZES NORMAL. (X)