59-12-02 LOCKHEED: Applies to All Models 049, 149, 649, 749 and 1049 Series Aircraft.
Compliance required as indicated.
The following inspections have been established as a result of recently found corrosion and cracking on the wing Station 80 bathtub fittings, P/N's 251245 and 251246 on Model 049, 149, 649, 749 Series aircraft and Model 1049-54 aircraft and P/N's 310008 and 310009 on the remaining Model 1049 Series aircraft.
These inspections shall be accomplished on all aircraft which have accumulated 12,000 or more flight-hours. Inspect affected aircraft at the next block overhaul or within 4,000 flight-hours, whichever occurs first.
Inspect all aircraft for cracked bathtub fittings as follows:
(1) Inspection may be made by removing the wing-to-fuselage fillet and dye checking the forward and aft edges on the neck of the bathtub fittings lugs of both the inner and stub wing fittings.
(2) Replace any cracked bathtub fittings.
Inspect each inner wing andstub wing Station 80 fitting for corrosion as follows:
(1) Visually inspect the inner and stub wing Station 80 joint bathtub fittings adjacent to the DD8 rivets and rivet attachments taking particular care to note any imperfections or paint defects. Probe further whenever defects in paint are discovered in order to detect any corrosion.
(2) Replace any wing Station 80 bathtub fittings on which corrosion cleanup exceeds a depth of 0.025-inch or a diameter of 0.70 inch (approximate diameter of a dime) around rivet attachments. Remove corrosion if within the allowable and treat per Lockheed Report 8882, (also 7789 and 5886) paragraph 1-67N, revised July 15, 1957, or equivalent.
(3) Inspect the stub wing and inner wing skin upper surface for corrosion around the bathtub fitting screw holes. Also inspect the stub wing and inner wing upper skin lower surfaces between corrugations for corrosion. Maximum allowable skin cleanup without resorting to a doubler repair is 0.020-inch deep or an area not exceeding one inch wide and three inches long, provided screw holes are not enlarged. Areas of skin corrosion exceeding these allowable limits should be repaired in accordance with applicable Structural Repair Manual procedures. Clean up and protect corroded areas per Lockheed Report 8882, (also 7789 and 5886) revised July 15, 1957, or equivalent. It must be determined that any corrosion is confined to the skin only and does not penetrate into the corrugations. Reinstall all screw attachments flush in to the cleaned up areas.
(4) Inspect the bathtub fitting end lugs for corrosion. Maximum permissible combined depth of corrosion on mating fitting lugs should not be such as to increase the total gap between mating faces in excess of 0.020 inch. Replace fittings which cannot be cleaned up within this tolerance.
The special inspection note above may be extended an additional 12,000 flight-hours for each wing on which all fittings are replaced. Otherwise reinspection at 4,000 flight-hour periods or block overhaul whichever occurs first is required to insure detection of cracked or corroded Wing Station 80 bathtub fittings or attachments.
(Lockheed Service Letter FS/231053 covers this same subject.)