# Airworthiness Directives; Sikorsky Aircraft Corporation Model S-76A, B, and C Helicopters
> **Rule** · Final rule. · Published 2010-05-13 · Effective 2010-06-17 · 75 FR 26885
## Document
- **Document number:** 2010-10588
- **Category:** airworthiness
- **Manufacturer:** Sikorsky
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 75 FR 26885
- **Publication date:** 2010-05-13
- **Effective date:** 2010-06-17
- **FAA docket:** Docket No. FAA-2006-24587
## Abstract

This amendment adopts a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-76A, B, and C helicopters that requires inspecting each installed Woodward HRT (formerly HR Textron) main rotor servo actuator (servo actuator) for a high rate of leakage and replacing each affected servo actuator with a servo actuator containing a newly re-designed servo actuator piston. This amendment is prompted by a National Transportation Safety Board (NTSB) Safety Recommendation issued in response to an accident involving a Model S-76C helicopter. In the NTSB Safety Recommendation, the performance of a servo actuator piston upon reaching 3,000 hours time-in-service (TIS) was questioned as a result of piston head seal leakage and piston head plasma spray flaking. The actions specified by this AD are intended to prevent degraded servo actuator performance as a result of piston head seal leaking and plasma spray flaking, which could result in subsequent loss of control of the helicopter.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2010/05/13/2010-10588/airworthiness-directives-sikorsky-aircraft-corporation-model-s-76a-b-and-c-helicopters)
---
*AI Analytics · CC0 1.0*