# AD 75-17-21: Cabin Pressurization

- Type: Airworthiness directive
- Status: Current
- Products: Textron BH.125 Series 400A, BH.125 Series 600A, 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: August 19, 1975
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- Amendment: 39-2323
- Registered aircraft: 4 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/6D2F8FAB3AACD747862569A4006ECC2F.0001
- DRS record last changed: January 21, 2026
- Page: https://openairdocs.org/ad/75-17-21

## The airworthiness directive

75-17-21 HAWKER SIDDELEY AVIATION, LTD: Amendment 39-2323. Applies to DH-125 and BH-125 airplanes certificated in all categories.

Compliance required as indicated.

To prevent possible rapid loss of cabin pressurization, accomplish the following:

Within 50 hours time in service after the effective date of this AD, unless already accomplished, inspect all Hellerman type cabin pressure seal bungs for displacement and rework as necessary in accordance with the following:

  (a) Locate all Hellerman type cabin pressure seal bungs for the particular aircraft being inspected.

NOTE: Refer to the relevant aircraft wiring diagram manual (2 volumes) and to the maintenance practices in the Maintenance Manual, Chapter 24-00 (all series pre-600) and Chapter 24-01 (series 600). Pressure bung installations may be of the normal or reverse type assembly as defined in the Maintenance Manual reference noted in paragraph (c) of this AD. The total number may vary from one airplane toanother depending on the electrical equipment installed.

  (b) Gain access to the bungs in accordance with the procedures in the Maintenance Manual, Chapters 24 and 25.

  (c) Inspect the bungs (both normal and reverse assemblies) for displacement and reinspect and/or rework as necessary in accordance with the instructions contained in Part B of temporary revision dated April 1, 1975, to HSA Maintenance Manual, Chapter 24-00 (all series except 600) and Chapter 24-01 (series 600), or the appropriate sections of the referenced chapters if the temporary revision has been incorporated into the HSA Maintenance Manual, or an FAA-approved equivalent.

  (d) Where pressure bung(s) have been removed for rework, upon re-installation of the pressure bung(s) conduct a cabin leak rate check in accordance with the appropriate provisions of chapter 21 of the HSA Maintenance Manual prior to further flight to ensure the integrity of the pressure cabin.

This amendment becomes effective August 19, 1975.

## 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 10 of 50 models: DH.125 Series 1A/R-522, BH.125 Series 400A, BH.125 Series 600A, DH.125 Series 400A, DH.125 Series 3A/R, DH.125 Series 1A, DH.125 Series 1A-522, DH.125 Series 3A…

## 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/75-17-21/models.md
Every aircraft: https://openairdocs.org/ad/75-17-21/aircraft.md

Its text cites no advisory circulars or STCs.

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