AD 55-23-03
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Lockheed Aircraft Corporation | 1049-54 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049B-55 (Navy R7V-1) | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049C-55 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049D-55 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049E-55 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049F-55 (USAF C-121C) | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049G-82 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 149-46 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 49-46 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 649-79 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
Unsafe Condition
Cracks in the threaded portion of the main landing gear downlock spring cylinder assembly rod end P/N 295168 could result in failure of the downlock mechanism, leading to unintended gear retraction.
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Required Actions
Conduct magnetic particle or magnaglow inspections on the main landing gear downlock spring cylinder assembly rod end P/N 295168 for cracks. Replace cracked parts immediately. Repeat inspections at 300-hour intervals until replacement with P/N 475211 is done. Replace the assembly with P/N 475211 within the next 2,500 hours, ream lugs on the downlock strut assembly to 0.3770-0.3780 inch diameter, replace spacer P/N 268225-2 with bushing P/N LS3859-4-1094, and replace bolt AN 23-21 with AN 23-22.
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Compliance Time
As soon as possible but not later than next 250 hours for initial inspection. Replacement required within next 2,500 hours or next progressive/base overhaul period.
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Affected Aircraft
Lockheed Models 49, 149, 649, 749, and 1049 Aircraft with serial numbers 1963-1980, 2021-2088, 2503-2590, 2610, 2611, 2614-2677, 4001-4024, 4163-4166, 4501-4581, 4583-4594, 4602-4604, and 4613-4615.
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Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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