Originally Posted by
hoistop
... in other words, did rotation of (undone) control shaft strain seals of hydraulic cylinder in a way they are not designed to or not? It is an important question. If answer is yes, it means that in case this failure occured in cruise and pilot managed to somehow maintain (some) control, he might be soon faced with massive hydraulic leak - loss of hyd. system as a consequence. If this servoactuator is powered by both hyd systems, (two pistons one on top of other and dual spool valves as in standard dual servoactuators) both systems would probably soon leak hyd. fluid, rendering helicopter uncontrollable.
I don't know the inner workings of exactly how the inner shaft is coupled to (and therefore pushed/pulled by) the hydraulic actuator and whether rotating the inner shaft could cause a leak, however the Hydraulic system #1 has an automatic TR shut off valve (TRSOV in the diagram). If pressure drops at the TRA pressure switch, or the system level drops to a pre-determied level the TRSOV closes to maintain the remaining system #1 hydraulic fluid within the main rotor actuators to maintain main rotor control.
I.e. a catastrophic loss of the TR hydraulic servo would not in itself lead to a loss of main rotor hydraulics. Such a leak would however lead to a loss of system #2 pressure as there is no TRSOV on that system, so you would lose MR hydraulic redundancy.
