Airworthiness Directives; Empresa Brasileira de Aeronautica S.A. (EMBRAER) Model EMB-135BJ and EMB-145XR Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain EMBRAER Model EMB-135BJ and EMB-145XR series airplanes, that requires repetitive inspections for cracking in the firewall of the auxiliary power unit (APU), and repair of the firewall if necessary. This action also provides an optional terminating action for the repetitive inspections. This action is necessary to detect and correct cracking in the APU firewall, which could result in reduced structural integrity of the firewall, and a consequent uncontained APU fire that could spread to the airplane structure. This action is intended to address the identified unsafe condition.