52-12-03 LOCKHEED: Applies to Models 49-46, 149-46, 649-79, 649A-79, 749-79, 749A-79, C-121A, and VC-121B Aircraft.
Compliance required as indicated.
Inspect the following by August 1, 1952:
1. Bulkhead ring at Station 527.6 for cracks in channel bend radius P/N 283984-2 and -3 for Models 49 and 149, and P/N 285772-2 and -3 for all other models, as well as bracket P/N 252886 for all models.
2. Inspect for and replace any missing or broken screws through the outer flange of the bulkhead 527 visible under fillet.
If no cracks are found on first inspection, reinspect at 2,000-hour intervals until total airplane time reaches 8,000 hours. After 8,000 hours, reinspect at approximately 600-hour intervals. If cracks are found, operation may continue prior to repair provided cracks are marked and reinspected at approximately 200-hour intervals and, further, provided: (1) Total length of all cracks on one side of airplane does not exceed sum of 2 1/2 inches not counting cracks, if any, in bracket 252886; (2) Cracks in bracket 252886 left or right do not exceed sum of 2 inches. If cracks exceed either 2 1/2 inches in the channel or 2 inches in bracket, repair by either the interim fix method or final fix. The interim fix may be accomplished by bolting steel blocks tightly to each side of bulkhead ring webs in the vicinity of the cracks, with additional bolts through the steel flange of the ring and tapped into the steel blocks.
(Lockheed Service Bulletin No. 49/SB-714 covers this repair.)
The final fix consists primarily of replacing the aluminum alloy bracket, P/N 252886, with a heat-treated alloy steel bracket of approximately the same dimensions except for gage, and adding 0.078 inch heat-treated alloy steel doublers to the cracked channels, all parts securely bolted together.
(Lockheed Service Bulletin No. 49/SB-715 describes this reinforcement.)
If the interim fix as described by Lockheed Service Bulletin No. 49/SB-714, or equivalent, has been complied with, the inspection period may be increased to approximately 400-hour intervals until the final fix is applied. If the final fix, as described in Service Bulletin No. 49/SB- 715, or equivalent, is complied with, no further inspections are necessary.
The term "approximately" is used in connection with the inspection periods to provide flexibility so that these periods may be integrated with operators' regular inspection periods, nearest to the periods specified herein.