47-49-12 LOCKHEED: (Was Service Note 12 of AD-763-3.) Applies to All Models 49, 649, and 749 Serials Which Incorporate Short Type Metal Aft Doors for the Main Landing Gear.
At periods not to exceed 250 hours inspect the metal aft doors of the main landing gear for signs of cracks in the vicinity of the forward hinge attachments. When cracks are found, satisfactory reinforcements and doublers should be installed.
When doublers have been installed (doublers only are necessary if the doors are not already cracked) the periodic inspections may be discontinued.
(LAC Service Bulletin 49/SB-274 covers this same subject.)