Airworthiness Directives; The Boeing Company Airplanes

We are superseding Airworthiness Directive (AD) 2012-24-10 for certain The Boeing Company Model 747-400 and -400F series airplanes. AD 2012-24-10 required installing new software, replacing the duct assembly with a new duct assembly, making wiring changes, and routing certain wire bundles. This new AD retains the requirements of AD 2012- 24-10 and requires installing a new or serviceable pressure switch bracket and altitude pressure switch. This new AD also adds an airplane to the applicability. This AD was prompted by reports of intermittent or blank displays of a certain integrated display unit (IDU) that were due to an intermittent false electrical ground that was not addressed by the software installation or wiring changes required by AD 2012-24- 10. We are issuing this AD to prevent IDU malfunctions, which could affect the ability of the flightcrew to read primary displays for airplane attitude, altitude, or airspeed, and consequently reduce the ability of the flightcrew to maintain control of the airplane.