# AD 56-26-01: Main Relay Box Rework

- Type: Airworthiness directive
- Status: Current
- Products: Lockheed 1049-54, 1049B-55 (Navy R7V-1), 1049C-55, 1049D-55, 1049E-55, 1049F-55 (USAF C-121C), 1049G-82 and 1049H-82
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- Registered aircraft: 1 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/B6F6624CD062B42A8625696D0071AD21.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/56-26-01

## The airworthiness directive

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.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS 6A5](https://openairdocs.org/tcds/6A5): Lockheed Martin Aeronautics Company; names 8 of 8 models: 1049G-82, 1049C-55, 1049E-55, 1049F-55 (USAF C-121C), 1049D-55, 1049B-55 (Navy R7V-1), 1049H-82, 1049-54

## Registered aircraft it may apply to (OpenAirDocs)

Matched by airframe and engine model; the AD's applicability may narrow it by serial number, part number or equipment.

- Aircraft: 1 (1 by airframe model, 0 by engine model)
- Makers: Lockheed 1

Models with the most aircraft:

- [Lockheed 1049H-82](https://openairdocs.org/model/lockheed-1049h-82): 1 aircraft (airframe model)

All 1 models: https://openairdocs.org/ad/56-26-01/models.md
Every aircraft: https://openairdocs.org/ad/56-26-01/aircraft.md

Its text cites no advisory circulars or STCs.

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