As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GEAR DOOR OPEN LIGHT ILLUMINATED IN FLIGHT. GEAR RECYCLED. EMERGENCY DECLARED. LIGHT REMAINED ILLUMINATED UNTIL DESCENT. CREW VERBAL GEAR UPLATCH CHECK WAS NORMAL. COULD NOT DUPLICATE. VERIFIED RIGHT MAIN LANDING GEAR DOOR POSITION SENSOR WAS OUT OF RIG. RIGGED TARGET AND SENSOR TO SPECS IAW DC-9 AMM 32-60-03-2-0201. FINAL DOOR INDICATION WAS NORMAL.