# Airworthiness Directives; Bombardier Model CL-600-2B19 (Regional Jet Series 100 & 440) Airplanes
> **Rule** · Final rule. · Published 2005-04-07 · Effective 2005-05-12 · 70 FR 17604
## Document
- **Document number:** 05-6686
- **Category:** airworthiness
- **Manufacturer:** Bombardier Model CL-600-2B19 (Regional Jet Series 100 & 440)
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 70 FR 17604
- **Publication date:** 2005-04-07
- **Effective date:** 2005-05-12
- **FAA docket:** Docket No. FAA-2004-19761
## Abstract

The FAA is adopting a new airworthiness directive (AD) for certain Bombardier Model CL-600-2B19 (Regional Jet Series 100 and 440) airplanes. This AD requires modification of the Auxiliary Power Unit (APU) cooling air exhaust. This AD is prompted by reports of incomplete drainage of the APU enclosure. We are issuing this AD to prevent a negative pressure condition from developing in the APU enclosure when the APU is operating on the ground, which could create a potential fire hazard if flammable liquid leakage occurs inside the APU enclosure and cannot be drained overboard.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/2005/04/07/05-6686/airworthiness-directives-bombardier-model-cl-600-2b19-regional-jet-series-100-and-440-airplanes)
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