Originally Posted by Fil
TAC's flaw IMHO is that it relies on engines data to sense aysmmetric thrust. If no data available, say engine separation or such severe damage that the sensors have exited the rear of the engine too etc then TAC cannot function.
Concorde had an "auto-rudder" function, that kicked in rudder in the case of an engine surge (which caused a very sudden and nasty yaw).
On the prototypes we had a separate auto-rudder computer, that used engine intake pressure sensor data. These turned out to be "somewhat" unreliable, although at least they stayed "in-situ" !
The whole lash-up was replaced on the preprod and production aircraft by a lateral accelerometer and a couple of circuit boards in the autostab. These fed straight into the PFCUs, so the function was independent of the autopilot.