To: Max Angle
I agree that uncommanded movement of both primary and secondary flight controls has happened in the past and it will continue to happen in the future. In this particular case I am addressing the secondary flight controls on the A-310 and the A-320. Although I specifically addressed the flap systems on both aircraft it applies to the slat system on the A-310. I am not familiar with the A-320 whether it has leading edge slats. So that this does not degenerate into a P*****g contest I will explain what I think should be done to counter the uncommanded movement of the secondary flight controls.
Axiom 1. If the computer fails and generates an uncommanded signal then the computer can not stop it. Axiom 2:If the uncommanded signal stems from an internal failure of the PCU then the computer can not stop it if the signal is to extend the flaps. If the flaps are extended and there is an internal failure of the PCU causing the flaps to retract the computer can sense this and stop the movement. This will provide sufficient time to make the necessary corrections.
In either case the movement is generated by the PCU. Both the flap and slat system have two different hydraulic modules connected to a hydraulic motor driving through a gearbox. If there is an internal failure of the hydraulic module then only one of the two motors will be commanded to rotate which means that any movement will be at half speed but could in fact be slower depending on the extent of the failure.
If the failure is in the computer the movement will be at half speed.
The secondary system is powered by three different hydraulic systems. The Green and the Yellow system power the Flap system and the Green and the Blue system power the Slat system.
If an uncommanded signal is generated on the flap system it is necessary to turn off both the Green and Yellow system. This will leave you operating on only one hydraulic system. Once both systems are off, turn one system on. If the movement continues then turn that system off and the other one on. Now you are operating on two systems. A similar action should be taken on the Slat system.
As I had previously stated the Air Canada A-320 suffered a flap retraction during takeoff. I do not know if it was an electronic failure or a hydraulic failure. The firm that developed the Slat drive system suffered an uncommanded extension of the Slats on their iron bird. It could have easily been an uncommanded retraction. In either case the computer could not identify the movement or even to stop it. Since the PCUs are almost identical between the Flap and Slat systems the same problem could happen on the Flap system.
