# AD 77-26-01: Oxygen Supply

- Type: Airworthiness directive
- Status: Current
- Products: Textron BH.125 Series 400A, DH.125 Series 1A, DH.125 Series 1A-522, DH.125 Series 1A/R-522, DH.125 Series 1A/S-522, DH.125 Series 3A, DH.125 Series 3A/R, DH.125 Series 3A/RA and DH.125 Series 400A
- Effective: January 3, 1978
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- Amendment: 39-3099
- Registered aircraft: 4 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/8E64A9E2E66D79D8862569A50070F9C1.0001
- DRS record last changed: January 21, 2026
- Page: https://openairdocs.org/ad/77-26-01

## The airworthiness directive

77-26-01 HAWKER SIDDELEY AVIATION, LIMITED: Amendment 39-3099. Applies to DH/BH-125 airplanes, all series except 600A and 700A and excluding those airplanes with Modification 252239 embodied which introduces the Walter Kidde supply valve.

Compliance is required as indicated unless already accomplished.

To ensure the retainment of the threaded insert and prevent possible sudden discharge of the high pressure oxygen supply into the crew compartment, accomplish the following:

  (a) Within 10 hours time in service after the effective date of this AD, locate the oxygen master supply valve and passenger supply valve, both P/N SDV 826-1, and check to assure that threaded insert in the gland bushing is secure and spot lock the insert all in accordance with the Section entitled "Accomplishment Instructions" of Hawker Siddeley Aviation, Limited Alert Service Bulletin 35-A25, dated October 13, 1977, or an FAA-approved equivalent.

  (b) Prior to installation of any oxygen supplyvalves from spares stock, unless already accomplished, check, tighten, and lock the insert in accordance with paragraph (a) of this AD.

This amendment becomes effective January 3, 1978.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS A3EU](https://openairdocs.org/tcds/A3EU): Textron Aviation Inc.; names 9 of 50 models: DH.125 Series 1A/R-522, BH.125 Series 400A, DH.125 Series 400A, DH.125 Series 3A/R, DH.125 Series 1A, DH.125 Series 1A-522, DH.125 Series 3A, DH.125 Series 1A/S-522…

## 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: 4 (4 by airframe model, 0 by engine model)
- Makers: Hawker Siddeley 4

Models with the most aircraft:

- [Hawker Siddeley BH.125-400A](https://openairdocs.org/model/hawker-siddeley-bh-125-400a): 2 aircraft (airframe model)
- [Hawker Siddeley DH.125-3A/RA](https://openairdocs.org/model/hawker-siddeley-dh-125-3a-ra): 2 aircraft (airframe model)

All 2 models: https://openairdocs.org/ad/77-26-01/models.md
Every aircraft: https://openairdocs.org/ad/77-26-01/aircraft.md

Its text cites no advisory circulars or STCs.

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