What was found
DURING ROUTINE TRAINING FLIGHT, TOWER REPORTED THE LT MLG INBOARD DOOR REMAINED OPEN AFTER LANDING GEAR EXTENSION. AIRCRAFT LANDED WITHOUT INCIDENT. INSPECTED AIRCRAFT AND FOUND LT MLG BELLCRANK P/N 400088-001 BROKEN. THIS ALLOWED SEQUENCE VALVE TO OPEN CAUSING MLG DOOR TO FREEFALL OPEN. THE SAME PROBLEM OCCURRED IN 1994 TO RT BELLCRANK WITH 4,266.3 HRS TT. THE REPLACEMENT LT BELLCRANK IS SUBSTANTIALLY IMPROVED OVER ORIGINAL PART. SUBMITTER RECOMMENDED A SERVICE BULLETIN TO REQUIRE FREQUENT INSPECTIONS OF ORIGINAL PARTS.