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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

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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.

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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

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Please also note that in case of a dual engine loss, the RAT is automatically deployed.

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  • $\begingroup$ 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 at 12:45
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    $\begingroup$ 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 $\endgroup$
    – ocirocir
    Feb 24 at 12:46

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