Airworthiness Directives; Boeing Model 747-200F and -400 Series Airplanes; Model 767-400ER Series Airplanes; and Model 777 Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 747-200F and -400 series airplanes; Model 767- 400ER series airplanes; and Model 777 series airplanes. This AD requires replacing the frequency converter(s) used to supply electrical power for utility outlets (for the galley, medical equipment, or personal computers) with modified frequency converter(s). This AD also requires any specified action and related concurrent actions, as necessary. This AD is prompted by a report that a hard short condition between the frequency converter's output and its downstream circuit breakers will produce a continuous current that could cause the undersized output wiring to overheat. We are issuing this AD to prevent the overheating of the frequency converter's undersized output wiring, which could lead to the failure of a wire bundle, and consequent adverse effects on other systems sharing the affected wire bundle.