Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 737 series airplanes. This proposal would require revising the FAA-approved Airplane Flight Manual (AFM) to provide the flightcrew with additional procedures for shutting down the auxiliary power unit (APU) when an APU fire is indicated. This proposal is prompted by reports indicating that a latent electrical failure exists in the fire extinguishing system for the APU; this failure could prevent the APU from shutting down and fire extinguishant from discharging into the APU compartment in the event of an APU fire. The actions specified by the proposed AD are intended to ensure that the flightcrew is provided with procedures for shutting down the APU in the event of an APU fire.