Taily & 411A,
WRT the RAAF B707 lost in training near East Sale - the major problem was that the rudder hyd power was not "switched off", rather the hydraulics were depressurised. It does have the same NETT effect - no hydraulics to the rudder - but during the hyd pressure decay period enough pressure remains to keep the rudder torque tube locked for quite a length of time. This means no manual rudder and no power rudder.
Just briefly, the B707 - 338 rudder in manual mode used a control tab to "fly" the rudder. This tab was actuated (simplification!!) by a long (30 ft or so) torque tube up the fin. In power mode, this torque tube was locked so that the tab acted in anti balance. When the rudder hydraulics were "switched off" by the control switch, the rudder hydraulic system was ported to return, immediately allowing the torque tube to unlock and provide manual (tab) control albeit at a considerably higher Vmca. When the hydraulics were depressurised with the rudder power switched on, either by accident or design, the torque tube would not unlock until comparatively low pressure leaving a "no mans land" with little or no rudder control possible. It was a regular base training demo.