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

Resumo

The FAA proposes to adopt 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 proposed AD would require 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 proposed AD also would require any specified action and related concurrent actions, as necessary. This proposed 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 circuit that could cause the undersized output wiring to overheat. We are proposing 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.