Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to certain EMBRAER Model EMB-135 and -145 series airplanes. The existing AD currently requires revising the airplane flight manual (AFM) to prohibit in-flight auxiliary power unit (APU) starts, and installing a placard on or near the APU start/stop switch panel to provide such instructions to the flightcrew. This proposed AD would add an optional revision to the AFM that allows limited APU starts and would add a terminating action. This proposed AD is prompted by the airplane manufacturer developing modifications that revise or eliminate the need for restrictions to in-flight APU starts. We are proposing this AD to prevent flame backflow into the APU compartment through the eductor during in-flight APU starts, which could result in fire in the APU compartment.