The European Aviation Safety Agency (EASA) is proposing an Airworthiness Directive for an Airbus A330/A340 Flight Control Primary Computer (FCPC) software update in the wake of the fatal accident involving Air France flight AF447.
EASA states that it has been determined that, when there are significant differences between all airspeed sources, the flight controls of an Airbus A330 or A340 aeroplane will revert to alternate law, the autopilot (AP) and the auto-thrust (A/THR) automatically disconnect, and the Flight Directors (FD) bars are automatically removed.
Further analyses have shown that, after such an event, 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 AP and A/THR. However, in some cases, the AP orders may be inappropriate, such as possible abrupt pitch command.
In order to prevent such events which may, under specific circumstances, constitute an unsafe condition, EASA issued AD 2010-0271 to require an amendment of the Flight Manual to ensure that flight crews apply the appropriate operational procedure.
Since that AD was issued, new FCPC software standards have been developed that will inhibit autopilot engagement under unreliable airspeed conditions. The proposed AD requires software standard up-grade of the three FCPCs by either modification or replacement. The Proposed AD will be open for consultation until 30 August 2011.