AD 56-26-01
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Lockheed Aircraft Corporation | 1049-54 | LOCKHEED Model 1049 Series Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049B-55 (Navy R7V-1) | LOCKHEED Model 1049 Series Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049C-55 | LOCKHEED Model 1049 Series Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049D-55 | LOCKHEED Model 1049 Series Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049E-55 | LOCKHEED Model 1049 Series Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049F-55 (USAF C-121C) | LOCKHEED Model 1049 Series Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049G-82 | LOCKHEED Model 1049 Series Aircraft |
| aircraft | Lockheed Aircraft Corporation | 1049H-82 | LOCKHEED Model 1049 Series Aircraft |
Unsafe Condition
The relays in the generator feeder protection main relay box are capable of overheating at high generator output, which could become excessive when one or more generators become inoperative, leading to potential complete electrical outage in the vital DC bus area.
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Required Actions
Install a blower and replace existing interconnecting bus bars with new ones having increased cooling areas, or use an equivalent means approved by the FAA Chief, Engineering and Manufacturing Branch, Western Region.
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Compliance Time
as soon as possible but not later than the next block overhaul or major inspection period after parts become available
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Affected Aircraft
Lockheed Aircraft Corporation Model 1049 Series Aircraft, LAC Serial Numbers 4501 Through 4565, 4572 Through 4647 and 4163 Through 4166
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Federal Register Abstract
Main Relay Box Rework
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_56-26-01.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 56-26-01 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: LOCKHEED Model 1049 Series Aircraft Subject: Main Relay Box Rework 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: AIRWORTHINESS DIRECTIVES FINAL RULES: 56-26-01 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 56-26-01 SUBJECT HEADING: LOCKHEED Model 1049 Series Aircraft ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 56-26-01 LOCKHEED: Applies to Super Constellation 1049 Series Aircraft, LAC Serial Numbers 4501 Through 4565, 4572 Through 4647 and 4163 Through 4166. Compliance required as soon as possible but not later than the next block overhaul or major inspection period after parts become available. The relays housed within the generator feeder protection main relay box have been found capable of overheating at high generator output. This could become excessive when one or more generators become inoperative. This box contains the main DC bus, which is the tie-point of all primary electric power for the airplane. To minimize the probability of complete electrical outage in this vital area, greater heat transfer capability shall be provided either by installing a blower and replacing the existing interconnecting bus bars with new bus bars having increased cooling areas, or by an equivalent means approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region. (Lockheed 1049 Service Bulletin No. 2838, dated August 20, 1956, contains FAA- approved rework information for compliance with this AD.) This airworthiness directive does not apply to aircraft equipped with two 11 KVA alternators. Revised July 25, 1962. FOOTER:
Document Text
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AD Final Rules - DRS_56-26-01.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 56-26-01 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: LOCKHEED Model 1049 Series Aircraft Subject: Main Relay Box Rework 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: AIRWORTHINESS DIRECTIVES FINAL RULES: 56-26-01 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: AD NUMBER: 56-26-01 SUBJECT HEADING: LOCKHEED Model 1049 Series Aircraft ACTION: SUMMARY: DATES: ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 56-26-01 LOCKHEED: Applies to Super Constellation 1049 Series Aircraft, LAC Serial Numbers 4501 Through 4565, 4572 Through 4647 and 4163 Through 4166. Compliance required as soon as possible but not later than the next block overhaul or major inspection period after parts become available. The relays housed within the generator feeder protection main relay box have been found capable of overheating at high generator output. This could become excessive when one or more generators become inoperative. This box contains the main DC bus, which is the tie-point of all primary electric power for the airplane. To minimize the probability of complete electrical outage in this vital area, greater heat transfer capability shall be provided either by installing a blower and replacing the existing interconnecting bus bars with new bus bars having increased cooling areas, or by an equivalent means approved by the Chief, Engineering and Manufacturing Branch, FAA Western Region. (Lockheed 1049 Service Bulletin No. 2838, dated August 20, 1956, contains FAA- approved rework information for compliance with this AD.) This airworthiness directive does not apply to aircraft equipped with two 11 KVA alternators. Revised July 25, 1962. FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
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