Savoia
I will try to explain simply (the memory banks are a little cloudy). The Secondary servo pack is situated between the pilots at about shoulder height just above the main drive shaft running between the coupling gearbox and the main rotor gearbox.
It can be moved by the pilot or the Auto stabilizing System, the ASE has two (Civil) or three (Military) electrical servo motors which will move the pilot valve to help fly the aircraft.
With this arrangement a Stick Jump Check was called for by the Pilot on a daily basis. The Pilot did this and discovered a large stick jump. As the system was new the Engineer flying with the aircraft spoke with the engineers at North Denes and it was decided to adjust the pilot valves to try and eliminate the stick jump.
The impression that I got when I joined the Company 6 months later was that this was something new and unknown, the fault diagnosis in the Manual was a bit vague so they proceeded with an adjustment.
It would seem that a combination of errors, i.e. servo motor operating outside its proper range, a vague procedure, and an adjustment too great that when the secondary hydraulics was switched off the aircraft controls were outside their operating range and the aircraft crashed and burned. The Pilot and Engineer were both badly burnt but both returned to work after quite a long time recovering.
After this event a 7 day hard-over check (Tech. Memo 110) was started, a Hard-over box was developed and the inspection was expanded to the check that I referred to previously. When I arrived at North Denes I was able to increase the knowledge a little as I used to set these servo units up on the bench. The RAF had similar problems with their servo motors going outside their operating range so a programme was set up to study and improve the reliability of the units.
One must remember that at this time electronics was something new, some of us could not even spell electronics or avionics let alone understand it.
David Gash