AF 447 Search to resume

[Machinbird]

The Shadow
My limited reading of Airbus FCOM tells me your description of a trim overload kickout does not apply to Airbus aircraft. There are a number of ways that autopilots control the forces, one of which is an electrical servo system that applies a mechanical force directly on the elevator control mechanism. This does not apply to Airbus.
The Airbus is a technologically sophisticated system that trims by moving the THS (Trimmable Horizontal Stabilizer). When a control input is made by the AP or crew, then one of the 3 PRIM computers looks at the control input and trades off a little elevator deflection for THS movement. The theory apparently being to keep the elevators near the center of their travel. The THS is controlled by a big screw jack driven by two hydraulic motors. It won''t ever get tired of holding that load. The THS is the 600 pound gorilla in the pitch control system but it moves slowly since you don't want to accidentally throw people through the overhead. Each side of the elevator is driven by two servo type hydraulic cylinders, electrically controlled, that permit relatively rapid control input. (Normally 1 cylinder works and one flutter damps). Since the elevator is electrically controlled (there is no direct mechanical connection between the "cockpit pitch control" and the elevator for a servo to act upon) the type of trim or force overload that was postulated does not exist. I've left out a lot of the meat and potatoes so see FCOM-Flight Controls for more detailed information.