A320 G+B and RAT deployment

[Higgs boson]

In a scenario of G+B dual hydraulic failure, assuming G system is lost due to low level and B system is lost either due to reservoir overheat or pump overheat, is deployment of RAT from HYD panel advisable? The FCOM checklist mentions " IF B SYS LOST BY ELEC PUMP LO PR: ......RAT MAN ON"....

My understanding is that the following cases will lead to B SYS LO PR
# In case of B electric pump overheat, the ECAM will instruct you to switch off B pump leading to system B system low pressure.
# B reservoir overheat also calls for B ELEC pump to be off and leads to B system low pressure.

Will following the ECAM and deploying the RAT aggravate the overheat condition?

[Goldenrivett]

“Will following the ECAM and deploying the RAT aggravate the overheat condition?”

No. From memory, I think the ECAM invitation to deploy the RAT only appears when Blue Reservoir overheat has extinguished. The original overheat was probably due to a problem with the Blue Electric pump.

[Fursty Ferret]

Don't forget that there's a difference between B SYS LO PR and B ELEC PUMP LO PR.

The ECAM has the condition statement: "If blue sys lost by ELEC PUMP LO PR", so the line to deploy the RAT manually shouldn't appear. Not on the A320 any more but I remember that hydraulic ECAMs were fairly straightforward.

If I'm wrong please correct my understanding because it's been three years.

Edit: crossed with goldenrivet. :)

[vilas]

There is RAT for Blue electric pump and PTU between G and Y EDPs and also electric pump for Yellow. The ECAM philosophy for the use of redundancy is same. They are only available if the main pump produces low pressure. They are to be switched off if the low pressure is due to reservoir low level and the system is lost. In case of reservoir overheat or reservoir air low pressure they are switched off till the condition disappears and then an attempt is suggested to recover the system.
The general logic is G and Y are main systems so their loss the system tries to recover, subject to conditions mentioned above automatically through PTU. In case PTU has a problem Yellow services are recovered through Yellow electric pump. Green having too many services is only recoverable through PTU. If not then services are lost. In case of single hydraulic B failure, since it doesn't have many services and the complications of unretractable RAT it's not recovered through RAT but taken as lost. Only in case of dual hydraulic failure ECAM tells you to recover the B through RAT. to bring it to single failure.

[Higgs boson]

If its a G+B failure and B sys is lost due to reservoir overheat, will ECAM ask you to deploy RAT?

[vilas]

The answer is No! ECAM will only ask you to switch off B electric pump.
During APP procedure it will ask you if blue overheat out then put B electric pump on, not the RAT.

[Higgs boson]

If I remember it correctly, switching off the B electric pump lead to B sys low pressure. This, coupled with the G HYD low level made the ECAM to display "RAT ON". My instructor had to specifically tell me not to deploy RAT because of the B reservoir overheat condition. Maybe its a simulator error. It felt odd not to follow the ECAM.

[vilas]

You may be having blue electric pump overheat and not reservoir overheat. If problem is with B Electric pump it is replaceable by RAT but for single B fail it will only ask you to switch off electric pump and accept the loss of B system. But if Blue loss is second system loss or blue loss is the first loss followed by G or yellow loss then it will ask for Blue electric pump off and RAT on. I hope it's clear now.

[Higgs boson]

What I understand from the above is, in case of HYD G+B Lo PR(B lost due to elect pump overheat), B elect pump off....RAT ON.
In the case of HYD G+B lo PR(B lost due to reservoir overheat), B electric pump off....But NO RAT!

[vilas]

Yes! That is correct.

[vilas]

Higgs boson

And when B reservoir overheat out B electric pump Auto.