Airworthiness Directives; Boeing Model 767-200, -300, -300F, and -400ER Series Airplanes

The FAA is superseding an existing airworthiness directive (AD), which applies to certain Boeing Model 767-200, -300, and -300F series airplanes. That AD currently requires reworking the surface of the ground stud bracket of the left and right transformer rectifier units (TRUs) and the airplane structure mounting surface, and measuring the resistance from the bracket to the structure and the ground lugs to the bracket using a bonding meter. This new AD revises the applicability of the existing AD to include additional airplanes and requires, among other actions, installation of a new ground stud bracket using faying surface bonding. This AD results from 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 TRUs/main battery charger (MBC) and the structure. We are issuing this AD to prevent depletion of the main battery while in flight, resulting from the loss of both TRUs and the MBC, and consequent loss of all DC power, which could impact the safe flight and landing of the airplane due to the loss of function or malfunction of essential/critical systems and displays in the cockpit.