"FAR 29 insist that every critical components and critical systems which may have an affect for flight safety must be designed to be failsafe or redundant system."
Just about every helicopter I can think of has a single control input into the main servo, the bolt comes out and that control channel becomes inoperative. I see no redundancy in this.
This includes modern designs such as the AW139.
FAR 29.695 Power boost and power-operated control system.
(a) If a power boost or power-operated control system is used, an alternate system must be immediately available that allows continued safe flight and landing in the event of-
(1) Any single failure in the power portion of the system; or
(2) The failure of all engines.
(b) Each alternate system may be a duplicate power portion or a manually operated mechanical system. The power portion includes the power source (such as hydraulic pumps), and such items as valves, lines, and actuators.
(c) The failure of mechanical parts (such as
piston rods and
links), and the jamming of power cylinders, must be considered
unless they are extremely improbable.
AW139 servo system is designed to release main control valve in case of jam. The first indication will be SERVO 1 or SERVO 2 caution illuminates. It is very important immediately to start monitory Hydraulic temperature on synoptic page (this is not instructed by QRH).
System pressure 3500 PSI is circulating all the time inside affected servo. This constant 3500 PSI flow continuously through the bypass channels begins to rapidly raise the temperature of a hydraulic fluid (expect 1 celsius degree per each 5 seconds). It is expected that quite quickly the hydraulic oil temperature exceeds 134 degrees Celsius and HYD OIL TEMP warning illuminates. Switch off affected system by moving affected SOV to CLOSE on HYD control panel. AW139 has a philosophy where hydraulic SOV switch has switched off the faulty side! AW139 QRH is not clear at all regarding this SERVO and HYD OIL TEMP cautions.
Far out from shore, in the middle of the night, so it is challenging to begin to read and understand what QRH tells you to do and what QRH tells not to do. This scenario should be trained for all crews during recurrent training. It is not so easy even case has been briefed before sim session.