# Airworthiness Directives; MD Helicopters, Inc., Helicopters
> **Rule** · Final rule. · Published 2013-02-08 · Effective 2013-03-15 · 78 FR 9309
## Document
- **Document number:** 2013-02582
- **Category:** airworthiness
- **Manufacturer:** MD
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 78 FR 9309
- **Publication date:** 2013-02-08
- **Effective date:** 2013-03-15
- **FAA docket:** Docket No. FAA-2012-0746
## Abstract

We are adopting a new airworthiness directive (AD) for MD Helicopters, Inc. (MDHI) Model 500N, 600N and MD900 helicopters to require determining the cure date for each NOTAR fan blade tension- torsion strap (T-T strap), establishing a calendar-time retirement life for certain T-T straps, reducing the retirement life of certain T-T straps, marking each T-T strap with the expiration date, creating a component record card for each T-T strap, and revising the airworthiness limitations section of the maintenance manual to reflect the changes to the retirement life. This AD was prompted by a report from the T-T strap manufacturer that, over a period of time, moisture may reduce the strength of a T-T strap. The actions are intended to prevent failure of a T-T strap, loss of directional control and subsequent loss of control of the helicopter.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2013/02/08/2013-02582/airworthiness-directives-md-helicopters-inc-helicopters)
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