Originally Posted by
nodrama
Both hydraulic system pumps are main transmission driven, so as long as the main rotor is turning there will be workable system pressure. Both hydraulic systems are completely separate.
The hydraulic systems can be turned off individually (this requires electrical power, as the solenoids fail ‘open’), but cannot be turned off at the same time due to an automatic logic protection system. Nor can a hydraulic system be manually turned off if the logic protection system detects that the other hydraulic system has low oil contents, low pressure or high temperature.
It seems to me that the manufacturer has gone to lengths to ensure that at least one hydraulic system is available for the tail rotor control at all times.
My honest answer to your question about manual control with a dual hydraulic failure, is that I don’t know.
Originally Posted by nodrama
It isn't possible to even move the flying controls on an AW169 without at least one hydraulic system pressurised. That's why I made the point of saying earlier that the MR/ TR pitch control is hydraulically operated and NOT hydraulically assisted. There is a major flying control design difference. The pilot input isn't direct to the rotor pitch control, but to the hydraulic servo input valves. If the pressurised servos aren't commanded to move, nothing is moving. That's why there are two systems, for redundancy. How much clearer does it have to be?
I think we all understand.