Airworthiness Directives; British Aerospace (Jetstream) Model 4101 Airplanes

This amendment supersedes an existing airworthiness directive (AD), applicable to certain British Aerospace (Jetstream) Model 4101 airplanes, that currently requires repetitive detailed visual inspections to detect cracking or other damage of certain diaphragm support structures of the forward equipment compartment; and repair, if necessary. This amendment continues to require repetitive inspections, but also requires replacement of cracked or damaged diaphragm support structures with improved parts, which terminates the requirement for repetitive inspections. This amendment also adds airplanes to the applicability of the AD. This amendment is prompted by the development of improved diaphragms. The actions specified by this AD are intended to prevent failure of the two diaphragms that support the upper structure of the forward equipment compartment, which could accelerate fatigue damage in adjacent structure and result in reduced structural integrity of the airframe.