# AD 49-06-04: Altitude Compensating Bellows

- Type: Airworthiness directive
- Status: Current
- Products: Aero Spacelines 377, 377MG and 377SGT
- Published: June 17, 1950
- Issued: June 17, 1950
- Superseded by: Nothing supersedes this AD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/64C532C4B70198198625682A006466B6.0001
- DRS record last changed: November 21, 2025
- Page: https://openairdocs.org/ad/49-06-04

## The airworthiness directive

49-06-04 BOEING: Applies to Model 377 Aircraft. The 11 convolution type altitude compensating bellows, Bendix P/N 390935, shall be replaced with new bellows after each 100 hours of operation until the 9 convolution type Bendix P/N 391003 is available and has been installed in the carburetor.

## 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/49-06-04/models.md
Every aircraft: https://openairdocs.org/ad/49-06-04/aircraft.md

Its text cites no advisory circulars or STCs.

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