What was found
WHILE CHANGING LANDING LIGHT, FOUND LAMP RETAINER CRACKED AROUND UPPER STUD AND AROUND SCREW HOLE. THIS CONDITION CAUSED LANDING LIGHT TO VIBRATE EXCESSIVELY, PREMATURELY BURNING OUT BULB. SUBMITTER STATED THIS RETAINER SHOULD BE CHECKED AT EVERY INSPECTION, INCLUDING PRE-FLIGHT. IF RETAINER BROKE LOOSE, IT AND THE LANDING LIGHT COULD POSSIBLY BECOME ENTANGLED IN THE PROP.