# Airworthiness Directives; Agusta S.p.A. Model AB412 Helicopters
> **Rule** · Final rule; request for comments. · Published 1999-12-20 · Effective 2000-01-04 · 64 FR 71012
## Document
- **Document number:** 99-32735
- **Category:** airworthiness
- **Manufacturer:** Agusta S.p.A. Model AB412
- **Type:** Rule
- **Action:** Final rule; request for comments.
- **Citation:** 64 FR 71012
- **Publication date:** 1999-12-20
- **Effective date:** 2000-01-04
- **FAA docket:** Docket No. 99-SW-63-AD
## Abstract

This amendment adopts a new airworthiness directive (AD) applicable to Agusta S.p.A. Model AB412 helicopters. This action requires removing and replacing certain main rotor yokes with airworthy main rotor yokes before further flight. This amendment is prompted by the fatigue failure of a main rotor yoke (yoke). Fatigue analysis indicates that certain yokes are on the low end of the manufacturer's tolerance for thickness and do not have the desired margin of safety. This condition, if not corrected, could result in fatigue failure of the yoke, loss of a main rotor blade, and subsequent loss of control of the helicopter.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/1999/12/20/99-32735/airworthiness-directives-agusta-spa-model-ab412-helicopters)
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