# Airworthiness Directives; Bombardier Inc. Airplanes
> **Rule** · Final rule. · Published 2012-09-17 · Effective 2012-10-22 · 77 FR 56989
## Document
- **Document number:** 2012-22335
- **Category:** airworthiness
- **Manufacturer:** Bombardier Inc.
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 77 FR 56989
- **Publication date:** 2012-09-17
- **Effective date:** 2012-10-22
- **FAA docket:** Docket No. FAA-2012-0267
## Abstract

We are adopting a new airworthiness directive (AD) for certain Bombardier Inc. Model DHC-8-400 series airplanes. This AD was prompted by reports that the automatic de-icing mode became unavailable due to a failure of the timer and monitor unit (TMU). This AD requires replacing the TMU. We are issuing this AD to prevent loss of the automatic de- icing mode and consequent increased workload for the flightcrew, which, depending on additional failures, could lead to loss of control of the airplane.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2012/09/17/2012-22335/airworthiness-directives-bombardier-inc-airplanes)
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