# AD 87-25-02: Ground Connections

- Type: Airworthiness directive
- Status: Current
- Products: Sikorsky S-76A and S-76B
- Effective: December 31, 1987
- Superseded by: Nothing supersedes this AD
- Product type: Aircraft, Rotorcraft
- Amendment: 39-5778
- Registered aircraft: 53 may be affected, by airframe or engine model (OpenAirDocs)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/2FBE80D4EF125CE086256A4D00745097.0001
- DRS record last changed: May 30, 2024
- Page: https://openairdocs.org/ad/87-25-02

## The airworthiness directive

87-25-02 SIKORSKY AIRCRAFT: Amendment 39-5778. Applies to all Model S-76A and S-76B series helicopters through and including serial number 760350, certified in any category.

Compliance is required within the next 25 hours' time in service after the effective date of this AD, unless already accomplished.

To prevent possible loss of AC electrical power due to 26 VAC transformer single ground connection failure, provide separate ground connections for 26 VAC transformers 1 and 2.

NOTE: Sikorsky Service Bulletin No. 76-24-5, AC Electrical Power System - AC Power Transformer Ground Wires Termination-Separation of, dated October 19, 1987, constitutes an acceptable means of compliance with this requirement.

This amendment becomes effective December 31, 1987.

## Affected data sheets (1) (OpenAirDocs)

The type certificate data sheets whose models the AD names.

- [TCDS H1NE](https://openairdocs.org/tcds/H1NE): Sikorsky Aircraft Corporation; names 2 of 4 models: S-76B, S-76A

## 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: 53 (53 by airframe model, 0 by engine model)
- Makers: Sikorsky 53

Models with the most aircraft:

- [Sikorsky S-76B](https://openairdocs.org/model/sikorsky-s-76b): 34 aircraft (airframe model)
- [Sikorsky S-76A](https://openairdocs.org/model/sikorsky-s-76a): 19 aircraft (airframe model)

All 2 models: https://openairdocs.org/ad/87-25-02/models.md
Every aircraft: https://openairdocs.org/ad/87-25-02/aircraft.md

Its text cites no advisory circulars or STCs.

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