# AD 91-14-12: Power System

- Type: Airworthiness directive
- Status: Current
- Products: Textron BH.125 Series 600A, HS.125 Series 600A and HS.125 Series 700A
- Effective: August 6, 1991
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Large airplane
- Amendment: 39-7053
- Docket: 91-NM-44-AD
- Registered aircraft: 22 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/2D0920E2B55F0F9F86256A09005E25C3.0001
- DRS record last changed: January 21, 2026
- Page: https://openairdocs.org/ad/91-14-12

## The airworthiness directive

91-14-12 BRITISH AEROSPACE: Amendment 39-7053. Docket No. 91-NM-44-AD.

Applicability: Model HS.125-600A and BH.125-600A series airplanes (Post Modification 252475) and Model HS.125-700A series airplanes (Post Modification 252509); as listed in British Aerospace Service Bulletin 24-279-3255A, dated November 16, 1990; certificated in any category.

Compliance: Required within 160 days after the effective date of this AD, unless previously accomplished.

To prevent loss of the standby constant frequency power system which provides the necessary back-up capability when the primary power system fails, accomplish the following:

A. Install a partial cover above the standby inverter "TF" located between frames 22 and 23 LH if the converter is installed as depicted on pages 5-6 of the service bulletin, in accordance with British Aerospace Service Bulletin 24-279-3255A, dated November 16, 1990.

B. An alternative method of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate.

NOTE: The request should be forwarded through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Standardization Branch.

C. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD.

D. The installation requirements shall be done in accordance with British Aerospace Service Bulletin 24-279-3255A, dated November 16, 1990. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from British Aerospace, PLC, Librarian for Service Bulletins, P.O. Box 17414, Dulles International Airport, Washington, D.C. 20041. Copies may be inspected at the FAA, Transport Airplane Directorate, Renton, Washington; or at the Office of the Federal Register, 1100 L Street N.W., Room 8401, Washington, D.C.

This amendment (39-7053, AD 91-14-12) becomes effective on August 6, 1991.

## 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 3 of 50 models: HS.125 Series 600A, HS.125 Series 700A, BH.125 Series 600A

## 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: 22 (22 by airframe model, 0 by engine model)
- Makers: British Aerospace 14, Hawker Siddeley 7, Raytheon 1

Models with the most aircraft:

- [British Aerospace HS 125-700A](https://openairdocs.org/model/british-aerospace-hs-125-700a): 14 aircraft (airframe model)
- [Hawker Siddeley HS.125 SERIES 700A](https://openairdocs.org/model/hawker-siddeley-hs-125-series-700a): 7 aircraft (airframe model)
- [Raytheon HS 125-700A](https://openairdocs.org/model/raytheon-hs-125-700a): 1 aircraft (airframe model)

All 3 models: https://openairdocs.org/ad/91-14-12/models.md
Every aircraft: https://openairdocs.org/ad/91-14-12/aircraft.md

Its text cites no advisory circulars or STCs.

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