Summary
We propose to supersede Airworthiness Directive (AD) 2012-24- 10, which applies to certain The Boeing Company Model 747-400 and -400F series airplanes. AD 2012-24-10 currently requires installing new software, replacing the duct assembly with a new duct assembly, making wiring changes, and routing certain wire bundles. Since we issued AD 2012-24-10, we have received new reports of intermittent or blank displays of a certain integrated display unit (IDU) that were due to an intermittent false ground not addressed by the software installation or wiring changes required by AD 2012-24-10. This proposed AD would retain the requirements of AD 2012-24-10 and would require installing a new or serviceable pressure switch bracket and altitude pressure switch, and add an airplane to the applicability of the existing AD. We are proposing 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.