# AD 78-08-01: Engine Blow-Off Valve Switches

- Type: Airworthiness directive
- Status: Current
- Products: Textron BH.125 Series 600A and HS.125 Series 600A
- Effective: May 10, 1978
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- Amendment: 39-3180
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/94491ACC98DE2B17862569A50076618A.0001
- DRS record last changed: January 21, 2026
- Page: https://openairdocs.org/ad/78-08-01

## The airworthiness directive

78-08-01 HAWKER SIDDELEY AVIATION LIMITED: Amendment 39-3180. Applies to BH/HS 125-600A airplanes, certificated in all categories.

Compliance required within one month after the effective date of this AD, unless already accomplished.

To prevent possible inability to activate the engine blow-off valve switches in the event that birds are ingested into the engines on take-off, accomplish the following:

Remove the existing switch guards for the engine blow-off valve switches and replace with the new design guard, P/N 25-6 NF 2629, in accordance with the section entitled "Accomplishment Instructions" and the associated drawing, contained in Hawker Siddeley Aviation, Ltd. Service Bulletin 75-3(2580), dated June 21, 1977, or an FAA-approved equivalent.

This amendment becomes effective May 10, 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 2 of 50 models: HS.125 Series 600A, BH.125 Series 600A

## Registered aircraft it may apply to (OpenAirDocs)

No registered aircraft matched the models it names.

Its text cites no advisory circulars or STCs.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.