59-18-04 LOCKHEED: Applies to All Models 1049C, 1049D, 1049E, 1049G and 1049H Aircraft.
Compliance required as indicated.
The following inspections have been established as a result of recently found cracking in the inner wing rear spar web at Wing Station 458.
At the next block overhaul or 4,000 flight-hours, whichever occurs first, on all aircraft (regardless of accumulated flight time) inspect the inner wing rear spar web at Station 458 for cracks in the upper and lower notched web area shown in Lockheed Drawing 555353. Inspection is applicable to both left and right wings.
If cracks are discovered incorporate the reinforcements shown in Lockheed Drawing 555353, or equivalent.
If no cracks are discovered, the reinforcements shown in Lockheed Drawing 555353 may be incorporated. Otherwise, reinspection at 4,000 flight-hour periods or block overhaul, whichever is less, is required to insure detection of cracks.
(Lockheed Service Letter FS/231094 covers thissame subject.)