Airworthiness Directives; Jetstream Model 4101 Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Jetstream Model 4101 airplanes, that 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. This amendment is 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 this AD are intended to prevent the failure of this intercostal during an emergency landing, which could consequently result in injury to the flight crew.