# AD 55-15-06: Cooling Air System Rework

- Type: Airworthiness directive
- Status: Current
- Products: Lockheed 1049C-55, 1049D-55, 1049E-55, 149-46, 49-46, 649-79, 649A-79, 749-79 and 749A-79
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- Registered aircraft: 2 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/044A7E12CEACDA578625696D0071AB1B.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/55-15-06

## The airworthiness directive

55-15-06 LOCKHEED: Applies to 049, 149 Aircraft, Serial Numbers 1963 Through 1980, 2021 Through 2088; 649-749 Aircraft, Serial Numbers 2503 Through 2590, 2610, 2611, 2614 Through 2618; 1049C Aircraft, Serial Numbers 4501 Through 4548; 1049E Aircraft, Serial Numbers 4549 Through 4555, 4558, 4559, and 4563 Through 4565; 1049D Aircraft, Serial Numbers 4163 Through 4166.

Compliance required by April 1, 1956, for Model 1049 aircraft and October 1, 1956, for Models 049/149 and 649/749 aircraft.

To improve the fire-resistance integrity of the above aircraft, revisions to the system supplying cooling air to the accessory section of the powerplant installation are considered necessary.

For 049-149 aircraft and 649-749 aircraft, the revision consists of installing a shutoff valve in a fireproof duct.

For the 1049C and E aircraft, the revision consists of replacing a section of aluminum duct between the oil cooler scoop, and the existing shutoff valve, with a fireproof duct. This section is in zone 1, and provides a possible zone 1 to zone 2 firepath.

Lockheed Service Bulletins 49/718, for 049/149 aircraft; 1049/2384, for 1049 aircraft; and 49/391A, for 649-749 aircraft, cover these subjects.

## Affected data sheets (2) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A-763](https://openairdocs.org/tcds/A-763): Lockheed Martin Aeronautics Company; names 6 of 6 models: 149-46, 649-79, 749A-79, 749-79, 649A-79, 49-46
- [TCDS 6A5](https://openairdocs.org/tcds/6A5): Lockheed Martin Aeronautics Company; names 3 of 8 models: 1049C-55, 1049E-55, 1049D-55

## 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: 2 (2 by airframe model, 0 by engine model)
- Makers: Lockheed 2

Models with the most aircraft:

- [Lockheed 49-46](https://openairdocs.org/model/lockheed-49-46): 1 aircraft (airframe model)
- [Lockheed 749-79](https://openairdocs.org/model/lockheed-749-79): 1 aircraft (airframe model)

All 2 models: https://openairdocs.org/ad/55-15-06/models.md
Every aircraft: https://openairdocs.org/ad/55-15-06/aircraft.md

Its text cites no advisory circulars or STCs.

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