# Airworthiness Directives; Sikorsky Aircraft Corporation (Sikorsky) Model S-70A and S-70C Helicopters
> **Rule** · Final rule. · Published 2010-11-17 · Effective 2010-12-22 · 75 FR 70101
## Document
- **Document number:** 2010-28458
- **Category:** airworthiness
- **Manufacturer:** Sikorsky
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 75 FR 70101
- **Publication date:** 2010-11-17
- **Effective date:** 2010-12-22
- **FAA docket:** Docket No. FAA-2010-0490
## Abstract

This amendment adopts a new airworthiness directive (AD) for the Sikorsky Model S-70A and S-70C helicopters. This AD requires an ultrasonic test (UT) inspection of the tail gearbox output bevel gear (gear) for a crack. If you find a crack, replacing the gear with an airworthy gear is required before further flight. This AD is prompted by three gear cracking incidents, one of which resulted in the tail rotor separating from the helicopter. The actions specified by this AD are intended to detect a crack in the gear to prevent a tail rotor separating, loss of tail rotor control, and subsequent loss of control of the helicopter.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2010/11/17/2010-28458/airworthiness-directives-sikorsky-aircraft-corporation-sikorsky-model-s-70a-and-s-70c-helicopters)
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