Mmmm ...
otter712 .... Ok here we go ...please listen very carefully as I will only say this once .....
......
I believe they are both active at all times. ... I believe you are WRONG!
Certainly they may both be pressurised at the same time but only System 1 is actively controlling the aircraft in 'normal operation'.
This from the Bk117 MBB Helicopter Training Centre Pilot course notes ....
For reasons of redundancy the hydraulic unit is constructed as a tandem system i.e. it consists of two separate systems which operate independently of each other. One of the systems (system1) is the MAIN system the other system (system 2) is the STANDBY system. Under normal operating conditions ONLY the MAIN system functions as the (controls) booster. If there is any malfunction within the MAIN system, it will be immediately cutoff and the standby system will be actuated automatically.
As with most duplicated systems on aircraft that are not designed to fly without hydraulic power to the flight controls a hydraulic system failure in flight IS A CRITICAL FAILURE A REQUIRES A LANDING ASAP.
Now this forum not the place to go into the intimate detail of the Hydraulic pack workings should you wish too ... please go back to whoever did your type training or find a knowledgable mechanic to take you through it.
I understand the Hydraulic packs on the EC145 are the same as for the BK117 but the 'pilot' valves instead of being activated by pushrods are controlled by 'teleflex cables' there may be some other subtle electronics interface bits added but I confess to not knowing about those on the EC145.
Cheers ... good luck ...
