Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain BAE Systems (Operations) Limited Model BAe 146 and Avro 146-RJ series airplanes. This proposal would require replacing the existing bellows inlet duct of the auxiliary power unit (APU) system with a new, improved rectangular metallic bellows inlet duct. This action is necessary to prevent air from the APU bay being ingested into the flight deck and passenger cabin resulting in poor air quality and, if the air is contaminated, possible incapacitation of the flightcrew and passengers. This action is intended to address the identified unsafe condition.