Airworthiness Directives; Boeing Model 747-200B, -300, -400, -400D, and -400F Series Airplanes

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 747-200B, -300, -400, -400D, and -400F series airplanes. This action requires repetitive inspections to detect cracking of fire extinguisher discharge tubes in certain engine struts, and corrective action, if necessary. For certain airplanes, this action also provides for a modification of the fire extinguisher discharge tubes, which constitutes terminating action for the repetitive inspections. This amendment is prompted by reports that cracked fire extinguisher discharge tubes have been found in the engine struts on certain airplanes. The actions specified in this AD are intended to detect and correct cracked fire extinguishing tubes in the engine struts. In the event of an engine fire, such cracked tubes could reduce the amount of fire extinguishing agent that can be delivered to the engine, and could result in a fire spreading from the engine to the wing of the airplane.