Airworthiness Directives; British Aerospace (Jetstream) Model 4101 Airplanes

This amendment revises an existing airworthiness directive (AD), applicable to certain British Aerospace (Jetstream) Model 4101 airplanes, that currently requires an inspection to determine the thickness of the intercostal that attaches the third crew member seat to the floor structure in the flight compartment, and replacement, if necessary. That action was prompted by a report from the manufacturer indicating that intercostals have been installed that are not of sufficient thickness (and consequent strength) to support the third crew member seat during emergency landing dynamic conditions. The actions specified by that AD are intended to prevent the failure of this intercostal during an emergency landing, which could consequently result in injury to the flight crew. This amendment revises the applicability of the existing AD by removing several airplanes.