Airworthiness Directives; Boeing Model 767-200, -300, and -300F Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Boeing Model 767-200, -300, and -300F series airplanes. This AD requires reworking the surface of the ground stud brackets of the transformer rectifier unit (TRU) and the airplane structure mounting surface, and measuring the resistance from the bracket to the structure and the ground lug to the bracket using a bonding meter. This AD is prompted by a report of loss of all direct current (DC) power generation during a flight, due to inadequate electrical ground path between the ground bracket of the TRU and the structure. We are issuing this AD to prevent depletion of the main battery and consequent loss of all DC power, which could cause the loss of flight critical systems.