Q1. Why is blue hydraulic system chosen for RAT out of the three. Q2. If in case of hydraulic emmergency if I push RAT switch on Emer Elec pannel what will happen
Because in A320 is the only hydraulic system independent from the engines and isolated from the other two hydraulic systems (while G and Y have the PTU in common). Also the B hydraulic system is able to control both elevators and ailerons, while Y cannot control ailerons and G controls only the left elevator. That's a design choice taking in account all the possible failures to reduce the risk of a triple hydraulic failure.
There are two switches that allow you to open the RAT:
- The RAT MAN ON (on HYD panel), which open the RAT and feeds the B HYD
- The RAT MAN ON (on EMER ELEC panel), which has the same effect of the previous one, but it also connects the emergency electrical generator
Please also note that in case of a dual engine loss, the RAT is automatically deployed.
$\begingroup$ I read somewhere that in case of electrical failure the electrical motor of blue hydraulic system stops so blue hydraulic failure occurs $\endgroup$ Feb 24, 2021 at 12:45
2$\begingroup$ Yes, and this is why you deploy the RAT in case of a dual engine failure, because you have no electrical power to run the B or Y elec pumps. As you can see in the diagram above, the RAT is alternative to the elec pump, so it can pressurize the B hyd system without the need of electrical power $\endgroup$– ocirocirFeb 24, 2021 at 12:46