Summary
We propose to adopt a new airworthiness directive (AD) for all Airbus Model A330-200, -200 Freighter, and -300 series airplanes; and Model A340-200, -300, -500, and -600 series airplanes. This proposed AD was prompted by a determination that, due to significant differences among all airspeed sources, the flight controls will revert to alternate law, the autopilot (AP) and the auto-thrust (A/THR) will automatically disconnect, and the flight director (FD) bars will be automatically removed. Then, if two airspeed sources become similar while still erroneous, the flight guidance computers will display the FD bars again, and enable the re-engagement of the AP and A/THR. In some cases, however, the AP orders may be inappropriate, such as possible abrupt pitch command. This proposed AD would require a software standard upgrade (modification or replacement) of the three flight control primary computers (FCPCs). We are proposing this AD to prevent autopilot engagement under unreliableairspeed conditions, which could result in reduced controllability of the airplane.