Are the two flight control systems completely independent of one another or is there some reason a complete fluid leak or loss of pressure on one system is able to cause problems on the remaining system?
Is there any place in the two systems where fluid could be passed to the other by a malfunction such as a leaking seal?
One would like to think they were truely separate and equal systems.
The early Chinooks had one place where a leaking seal could allow systems to transfer fluid but that very rarely happened and it did not cause either system to fail. The major symptom was one system showed overfull and the other always needed topping off.