Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Boeing Model 747-400, -400D, and -400F series airplanes. This proposed AD would require replacing at least one flap control unit (FCU) in the main equipment center with a new or modified FCU. This proposed AD is prompted by a report indicating that, after takeoff, an airplane was required to return to the airport because the autopilot disengaged. The report also indicated that, upon selecting flaps for landing, the flaps indication display did not indicate the flap setting, requiring the airplane to land in alternate flap mode. We are proposing this AD to prevent disconnection of autoland/autopilot functions and loss of primary flaps control and flaps indication display due to disengagement of all three FCUs at the same time, which could lead to a non-normal high speed landing with the flaps retracted, increased pilot workload, and possible runway departure at high speeds during landing.