Airworthiness Directives; Boeing Model 777 Airplanes

The FAA is revising an existing airworthiness directive (AD), which applies to all Boeing Model 777 airplanes. That AD currently requires a one-time inspection to determine the part number of the left and right air supply and cabin pressure controllers (ASCPCs), and installation of new ASCPC software if necessary. This AD requires those same actions. This AD also revises the existing AD to allow installation of an ASCPC with additional versions of software installed and to correct a part number reference. This AD results from a report of an ASCPC failure during flight. We are issuing this AD to prevent an ASCPC failure that could stop airflow into the airplane, inhibit the cabin altitude warning message, and cause an incorrect display of cabin altitude. These failures could result in depressurization of the airplane without warning.