# AD 52-12-01: Compressor Motors

- Type: Airworthiness directive
- Status: Current
- Products: Aero Spacelines 377, 377MG and 377SGT
- Published: December 4, 1956
- Issued: December 4, 1956
- Superseded by: Nothing supersedes this AD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/540B8920F05BFA598625682A0064D01A.0001
- DRS record last changed: November 21, 2025
- Page: https://openairdocs.org/ad/52-12-01

## The airworthiness directive

52-12-01 BOEING: Applies to all Model 377 Aircraft. Compliance required as specified below. In order to reduce the hazard of fire resulting from overheating of the freon compressor motors, compliance with the following is required: A. Compliance required before any installation of overhauled or new compressor motor after October 1, 1952. (Not required if item B accomplished or airplane operated in accordance item C.) Replace the following Westinghouse compressor motor magnesium parts with corresponding aluminum parts:

. . . . . . . . . . . . . . . . . P/N (Mg.) P/N (AL.) Inlet Cooling Cap P14A9709 P35A9046 Front Bearing Bracket P14A9712 P35A9044 Fan A14B3724 P35A9042

B. Compliance required prior to October 1, 1952. (Not required if both motors previously modified in accordance item A or if airplane operated in accordance item C.) Install a temperature sensing switch, adjusted to actuate at 100 degrees or less, in the cooling air outlet of each freon compressor motor. Install circuits and equipment so that this overheat switch, as well as the motor thermoguard switch, will illuminate a cockpit warning light or will open the compressor motor power circuit, or both. C. In the event the modifications outlined in A or B are not completed in accordance with the above requirements, aircraft may be operated with the refrigeration systems made inoperative.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A-812](https://openairdocs.org/tcds/A-812): Aero Spacelines Incorporated; names 3 of 3 models: 377, 377MG, 377SGT

## 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: Boeing 1

Models with the most aircraft:

- [Boeing 377MG](https://openairdocs.org/model/boeing-377mg): 1 aircraft (airframe model)

All 1 models: https://openairdocs.org/ad/52-12-01/models.md
Every aircraft: https://openairdocs.org/ad/52-12-01/aircraft.md

Its text cites no advisory circulars or STCs.

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