Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-300, -400, and -500 series airplanes, that requires an inspection to determine the type of topcoat material currently on the insulation of the inner wall of the fan duct cowl (the firewall) of the thrust reversers, and application of an improved topcoat material, if necessary. This amendment is prompted by tests, which demonstrated that flames can penetrate the firewall if certain combinations of insulation and topcoat materials are used. The actions specified by this AD are intended to prevent failure of the fireproof insulation top coat installed on the firewalls of the thrust reverser fan cowls, which could result in degradation or loss of the firewall and lead to an uncontained engine fire.