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 |
| aircraft | Lockheed Aircraft Corporation | 649A-79 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 749-79 | LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft |
| aircraft | Lockheed Aircraft Corporation | 749A-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.
AI-generated summary from the source AD text. Verify against the official source before acting.
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.
AI-generated summary from the source AD text. Verify against the official source before acting.
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.
AI-generated summary from the source AD text. Verify against the official source before acting.
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.
AI-generated summary from the source AD text. Verify against the official source before acting.
Federal Register Abstract
Landing Gear Cylinder Assy.
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_55-23-03.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 55-23-03 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft Subject: Landing Gear Cylinder Assy. Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: Make: Lockheed Aircraft Corporation Model: 1049-54 | 1049B-55 (Navy R7V-1) | 1049C-55 | 1049D-55 | 1049E-55 | 1049F-55 (USAF C-121C) | 1049G-82...Show more Product Type: Aircraft Product Subtype: Large Airplane Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: Updated RGL applicability to match AD applicability; CAR C-11-185 AIRWORTHINESS DIRECTIVES FINAL RULES: 55-23-03 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 55-23-03 SUBJECT HEADING: LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 55-23-03 LOCKHEED: Applies to Models 49, 149, 649, 749 and 1049 Aircraft, Serial Numbers 1963 Through 1980, 2021 Through 2088, 2503 Through 2590, 2610, 2611, and 2614 Through 2677, 4001 Through 4024, 4163 Through 4166, 4501 Through 4581, 4583 Through 4594, 4602 Through 4604, and 4613 Through 4615. Compliance required as indicated. 1. As soon as possible, but not later than next 250 hours conduct magnetic particle or magnaglow inspections on main landing gear downlock spring cylinder assembly rod end P/N 295168 for cracks in the threaded portion. If cracks are found replace the part immediately. Repeat inspection, magnetic particle or 20-power magnifying glass at 300-hour intervals until replacement in accordance with paragraph 2 is accomplished. 2. Replace downlock spring cylinder assembly P/N 270104 with new assembly P/N 475211 as soon as practical but not later than the next progressive or base overhaul period approximately 2,500 hours. Concurrently with this replacement, line ream the lugs on the downlock strut assembly to (0.3770 inch-0.3780 inch) diameter and replace the spacer P/N 268225-2 with bushing P/N LS3859-4-1094 and replace bolt AN 23-21 with AN 23-22 attaching the lower end of the spring cylinder assembly to the downlock strut. (Lockheed Service Bulletins 49/860 and 1049/2709 also cover this subject.) FOOTER:
Document Text
Show stored source text (verify against official source)
AD Final Rules - DRS_55-23-03.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 55-23-03 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft Subject: Landing Gear Cylinder Assy. Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: Make: Lockheed Aircraft Corporation Model: 1049-54 | 1049B-55 (Navy R7V-1) | 1049C-55 | 1049D-55 | 1049E-55 | 1049F-55 (USAF C-121C) | 1049G-82...Show more Product Type: Aircraft Product Subtype: Large Airplane Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: Updated RGL applicability to match AD applicability; CAR C-11-185 AIRWORTHINESS DIRECTIVES FINAL RULES: 55-23-03 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 55-23-03 SUBJECT HEADING: LOCKHEED Models 49, 149, 649, 749, and 1049 Aircraft ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 55-23-03 LOCKHEED: Applies to Models 49, 149, 649, 749 and 1049 Aircraft, Serial Numbers 1963 Through 1980, 2021 Through 2088, 2503 Through 2590, 2610, 2611, and 2614 Through 2677, 4001 Through 4024, 4163 Through 4166, 4501 Through 4581, 4583 Through 4594, 4602 Through 4604, and 4613 Through 4615. Compliance required as indicated. 1. As soon as possible, but not later than next 250 hours conduct magnetic particle or magnaglow inspections on main landing gear downlock spring cylinder assembly rod end P/N 295168 for cracks in the threaded portion. If cracks are found replace the part immediately. Repeat inspection, magnetic particle or 20-power magnifying glass at 300-hour intervals until replacement in accordance with paragraph 2 is accomplished. 2. Replace downlock spring cylinder assembly P/N 270104 with new assembly P/N 475211 as soon as practical but not later than the next progressive or base overhaul period approximately 2,500 hours. Concurrently with this replacement, line ream the lugs on the downlock strut assembly to (0.3770 inch-0.3780 inch) diameter and replace the spacer P/N 268225-2 with bushing P/N LS3859-4-1094 and replace bolt AN 23-21 with AN 23-22 attaching the lower end of the spring cylinder assembly to the downlock strut. (Lockheed Service Bulletins 49/860 and 1049/2709 also cover this subject.) FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
This site is not affiliated with or endorsed by the FAA. Always verify with official sources.
Related Airworthiness Directives
93-14-12
final ruleAirworthiness Directives; ESSEX PB&R CORPORATION (formerly E.I. DuPont de Nemours and Company \\nIncorporated) PELS Model 4566M37B Crewmember Protective Breathing Equipment (PBE) Units
Unsafe Condition: Leakage of the PBE neck seal could compromise the crew's ability to combat an aircraft fire.
71-07-02
final ruleLOCKHEED Models 49, 149, 649, 749, 1049, and 1649 Series Airplanes
Unsafe Condition: Failure to provide an acceptable obstacle clearance profile when computing the takeoff flight path.
67-03-05
final ruleLOCKHEED Models 649, 749, and 1049 Airplanes
Unsafe Condition: Propeller vibratory stresses due to continuous ground running between 2,300 and 2,650 r.p.m. with propeller governing and continuous static ground running in a crosswind above 2,650 r.p.m.
64-13-03
final ruleLOCKHEED Models 49, 149, 649, 649A, 749, 749A, 1049-54, 1049C, 1049D, 1049E, 1049G, and 1049H Series Aircraft
Unsafe Condition: Cracks and failure in the nose landing gear retract cylinder rod terminal ends (P/N 404052 or 1005032) due to fatigue.