# Airworthiness Directives; De Havilland Aircraft of Canada Limited (Type Certificate Previously Held by Bombardier, Inc.) Airplanes
> **Rule** · Final rule. · Published 2021-05-27 · Effective 2021-07-01 · 86 FR 28479
## Document
- **Document number:** 2021-11088
- **Category:** airworthiness
- **Manufacturer:** De Havilland
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 86 FR 28479
- **Publication date:** 2021-05-27
- **Effective date:** 2021-07-01
- **FAA docket:** Docket No. FAA-2021-0018
## Abstract

The FAA is superseding Airworthiness Directive (AD) 2015-17- 08, which applied to certain Bombardier, Inc. Model DHC-8-400 series airplanes. AD 2015-17-08 required installing new cable assemblies with a pull-down resistor. This AD requires modifications to the nose wheel steering (NWS) system. This AD was prompted by a report indicating that several failure modes of the NWS system may cause the loss of feedback from both rotary variable differential transformers to the steering control unit. The FAA is issuing this AD to address the unsafe condition on these products.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2021/05/27/2021-11088/airworthiness-directives-de-havilland-aircraft-of-canada-limited-type-certificate-previously-held-by)
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