# AD 77-13-11: Emergency Brake Control Valve

- 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: July 25, 1977
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- Amendment: 39-2936
- Registered aircraft: 4 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/244F66309847D3EB862569A5006548E1.0001
- DRS record last changed: January 21, 2026
- Page: https://openairdocs.org/ad/77-13-11

## The airworthiness directive

77-13-11 HAWKER SIDDELEY AVIATION, LTD: Amendment 39-2936. Applies to Model DH/BH-125 airplanes, all series, certificated in all categories.

Compliance is required as indicated, unless already accomplished.

To prevent possible failure of the knife edges of the emergency brake reducing valve, P/N AC.61516, and consequent complete loss of emergency braking capability without advance warning, accomplish the following:

  (a) Comply with paragraph (b) or (c) of this AD as follows, and, thereafter, continue to comply with paragraph (b) or (c) of this AD at intervals not to exceed 4500 landings since last compliance.

  (1) For airplanes having emergency brake control valve knife edges that have accumulated less than 4300 landings, since new, on the effective date of this AD, compliance is required prior to the accumulation of 4500 landings.

  (2) For airplanes having emergency brake control valve knife edges that have accumulated 4300 or more landings, since new, onthe effective date of this AD, compliance is required prior to the accumulation of an additional 200 landings.

  (3) For airplanes for which no records exist that indicate the number of landings the emergency brake control valve knife edges have accumulated, compliance is required prior to the accumulation of 200 landings after the effective date of this AD.

  (b) Replace the emergency brake control valve knife edges with new parts in accordance with Part A of Section 2 entitled "Accomplishment Instructions" of Hawker Siddeley Aviation, Ltd., Service Bulletin 32-167, dated January 27, 1976, or an FAA-approved equivalent.

  (c) Replace the entire emergency brake reducing valve, P/N AC.61516, with a valve fitted with new knife edges and install the valve in accordance with Part B of the section entitled "Accomplishment Instructions" of Hawker Siddeley Aviation, Ltd., Service Bulletin 32-167, dated January 27, 1976, or an FAA-approved equivalent.

This amendment becomes effective July 25, 1977.

## 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/77-13-11/models.md
Every aircraft: https://openairdocs.org/ad/77-13-11/aircraft.md

Its text cites no advisory circulars or STCs.

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