# Airworthiness Directives; De Havilland Aircraft of Canada Limited (Type Certificate Previously Held by Bombardier, Inc.) Airplanes
> **Rule** · Final rule. · Published 2021-06-04 · Effective 2021-07-09 · 86 FR 29939
## Document
- **Document number:** 2021-11674
- **Category:** airworthiness
- **Manufacturer:** De Havilland
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 86 FR 29939
- **Publication date:** 2021-06-04
- **Effective date:** 2021-07-09
- **FAA docket:** Docket No. FAA-2020-0975
## Abstract

The FAA is adopting a new airworthiness directive (AD) for certain De Havilland Aircraft of Canada Limited Model DHC-8-400, -401, and -402 airplanes. This AD was prompted by a report of main landing gear (MLG) retractions after striking an obstacle or severe wheel imbalance after a tire failure. This AD requires inspections for correct height of the lock link over-center stop pin and for correct gaps of the left-hand and right-hand MLG downlock proximity sensors, replacement of the shim if necessary, corrective actions, and installation of a new, improved proximity sensor electronic unit (PSEU) with software changes. The FAA is issuing this AD to address the unsafe condition on these products.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2021/06/04/2021-11674/airworthiness-directives-de-havilland-aircraft-of-canada-limited-type-certificate-previously-held-by)
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