A320 RAT

[scheini111]

Hey,

is there a difference when I deploy the RAT manually from the EMER ELEC PWR panel or the hydraulic panel?

My captain told me that tgere is a difference but i didnt found an information in the FCOM.

Best regards

[Amadis of Gaul]

Look in the FCOM more carefully.

[airnexus]

Hi, The difference is that from the HYD OVERHEAD PANEL you can deploy the RAT at any time and if you want to do it from the EMER ELEC PWR PANEL some condition must be met
-AC BUS 1 is not electrically supplied
-AC BIS 2 is not electrically supplied
-Aircraft speed is grater than 100kt

I hope this help

[scheini111]

Thank you for your response!!!!

Last time I had electricity as topic and the Captain said when I deploy the RAT via the hydraulic panel, the RAT only generates hydraulic pressure and when the RAT will be deployed by the EMER ELEC PWR panel the RAT only generates electricity, but I did not found if it is true or not. In the FCOM is under controls and indicator (hydraulic) written refer to controls and indicator (electricity) and in my mind there is no difference. If I understand correctly, the RAT generates hydraulic pressure and this pressure drives the blue system and the emergency generator in all cases.

Best regards

[gAMbl3]

If RAT is deployed manually from EMER ELEC PWR panel then it will pressurize the Blue Hyd system. Blue system will then power a hydraulic motor which runs the Emergency generator. There is a valve which opens and lets blue hydraulic to power the motor (Supply hydraulic power to CSM/G) if RAT is selected from EMER ELEC PWR panel. Also GCU will close the emergency generator line contactor if RAT is selected from EMER ELEC PWR panel (There is also AUTO logic for this). Selecting RAT Man ON on HYD panel will only deploy the RAT and pressurize the blue hyd system. It will not open the valve for the motor nor will the GCU close the line contactor. Hence on the HYD panel it says RAT MAN ON whereas on EMER ELEC PWR panel it says RAT & EMER GEN MAN ON (Auto).

Ref : FCOM DSC-24-10-30-30 EMER GEN Running.

[Rocket3837]

Hello scheini111,


I assume there is no fault with aircraft (ie AC 1+2 are powered and B HYD is powered as well) prior to pressing any RAT sw:


1. If U press the RAT sw on the HYD panel: nothing will happen other than the extension of the RAT. In this case the RAT will not power the B sys because it is already powered.
2. If U press the RAT sw on the ELEC panel: Again the RAT will extend but it will do nothing. However, the EMER GEN will be powered and coupled to the network (powered by the already running B sys). Auto decoupling of EMER GEN occurs at L/G extension or during landing roll at low speed (depends on how old is the aircraft)


Thanks

[Rocket3837]

caution: these SWs are powered by hot busses. In other words, if pressed the RAT will extend even with dead aircraft, even with BATTs selected OFF.

[vilas]

Rocket3837
With both gens powering their respective buses if RAT EMER gen is lowered manually what will EMER GEN power?

[Rocket3837]

Vilas,

Emer gen will power ac ess & dc ess.
correction to my previous post: everything will be normalized with L/G down regardless of aircraft MSN.


thanks

[vilas]

Rocket
With landing gear extension old RATs used to stall, the new once continue to function till 140 KTS. So why will everything be normal with gear down?

[No Fly Zone]

I hope that some A320 series drivers have read this original post, noted the responses and gone back to their books and then their tech ops folks. That some active drivers do not understand the sequence and What-ifs of the RAT system - and exactly what it will - and will not do, troubles me. As I read the details, dropping the RAT in a crunch is a great move; but if one does not take the secondary steps to direct the RAT's energy to the proper systems, hydraulic and/or electrical, the the device is essentially worthless.. That a couple of very honest folks do NOT know how to apply the RAT's energy capture to their systems is, at the least, commendable - and troublesome. Especially on the Bus, where nearly everything can be assigned to high-level automation, can they fly a limited airplane with only basic functions? Not INSTANTLY knowing how to apply the RAT's energy to needed services troubles me. Who direct's a faulted airplane's functions? Is it the crew, the faulty system, or nothing? That such event are exceedingly rare is just not quite good enough. Who is driving?:ugh:

[vilas]

No Fly Zone
Can you explain exactly what is your complaint?

[itsresidualmate]

If I recall correctly from my engineer's course, pressing either button simply activates a (different) solenoid to drop the RAT. Each release solenoid is supplied from a different hot bus. The reason there are two buttons is to make it simpler for you folks in an emergency; loss of electrics, press the ELEC button, loss of hydraulics, press the HYD button. Both buttons will give you the same thing though.

[itsresidualmate]

As an additional, I have come across issues in the past where the FCOM does not reflect the reality of the aircraft. The FCOM is written to help you folks deal with an emergency, it doesn't necessarily reflect how the aircraft systems work or are actually laid out.
The FCOM at first glance looks to be a handy little guide for us line engineers, but I know from experience that we engineers can't trust them to give us the whole story :)

[WhyByFlier]

No, no both buttons do not give the same thing. RAT MAN ON on the HYD section of the the overhead panel will deploy the RAT and give you BLUE hydraulic pressure only. It will NOT connect the EMER GEN when pushed. If you had a G and B HYD system failure (not loss of fluid) you may use the MAN ON switch to make it just a G HYD failure.

RAT MAN ON on the EMER ELEC CONTROL PANEL will deploy the RAT, pressurising the BLUE hydraulic system AND connect the EMER GEN. It was a question in type rating.

The initial responder's answer was not terribly clear or correct either. The RAT auto extends if both AC 1 and 2 are unpowered and the speed is above 100 kts. It's not a requirement in order for you to push the button - the switches are always powered - push them and the RAT will deploy.

[itsresidualmate]

Well, I've just had a look at the wiring manual; both buttons just operate the DEPLOY solenoids.

BUT, like I say, the reality of the aircraft doesn't always reflect the FCOM. I'd imagine there's a good reason you get taught to follow the FCOM and not the AMM :)

[itsresidualmate]

After a bit of digging in the wiring manual; looks like pressing the HYD button unlocks one solenoid and pops the RAT out giving Blue HYDS.
Pressing the ELEC button operates the second solenoid also popping the RAT out, but this switch also sends an input into the Constant Speed Gen.

So either switch will pop the RAT out, but only the ELEC will force the RAT Gen to power its respective systems. It looks like this is the reason for two switches; the RAT Gen takes priority over the systems it feeds.
So, having a HYD failure, pressing the HYD button will get the RAT out without force powering the RAT AC Gen. If you had a HYD failure and still had serviceable engine generators, but pressed the ELEC switch, you'd pop the RAT, still get hydraulics but you'd also force off the good engine generators (only on those bus bars the CSM/G supplies of course).
With HYDS taking priority over ELECS, the system logic would auto shut down the CSM/G if Blue HYDS reached a low pressure.

Clear as mud?!

[WhyByFlier]

So as I said and is described in FCOM! Thank you for giving the background info though.

[No Fly Zone]

I would certainly not call it a "complaint!!"
Some drivers simply do not know/understand enough detail about their systems to use them effectively if/when some component breaks. Virtually all drivers do just fine with routine operations or limited MELs. When stuff breaks, and without a detailed understanding of systems and their interactions, sometimes that QRH is just not enough. Different folks understand their airplanes at different levels. It was not meant as a complaint and I do not think most read it that way. Just sayin'... the top of the pack thoroughly understands the system's interactions - and well before a given button gets pushed. Regards,

[Rocket3837]

vilas,
my answer came in response to scheini111 (http://www.pprune.org/members/435852-scheini111) query which, as I interpreted it, was about what happens if any RAT SWs is pressed and I assumed he meant that the A/C has no fault prior to pressing the SWs.


1. If the RAT EMER GEN SW is pressed, RAT will drop and EMER GEN will activate and powers AC ESS until L/G is down then EMER GEN will deactivate.
2. If the HYD RAT SW is pressed, the RAT will extend and it will do nothing except rotating. It will not power the B HYD SYS because B sys is already powered by its own electrical pump. in this case, just assume the B ELEC pump PB is selected OFF then RAT will immediately power the B SYS.


Thanks

[vilas]

Rocker
Your first statement was correct. New aircraft EMER GEN doesn't deactivate at gear down.

[No Fly Zone]

"Can you explain exactly what is your complaint?"

Umm, sure... That otherwise excellent, type rated pilots apparently do not have a deep enough understanding of their machine's backup systems. You said, "complaint," sir, I did not. I'd call it a common concern. Sooner or later, that small, missing bit of functional detail will bite you.

[vilas]

No Fly Zone
Your mention of energy management of RAT is rather vague and appears like a general lament. If you could explain the precise concern will be better. I do believe in knowing details of the systems. But at least if you know what is being achieved by the ECAM procedure that is good enough. Normal and abnormal procedures are presented in much the same way as a car's user manual and if you don not have deeper understanding can leave you feeling uncertain despite completing the full procedure. May be that's what you meant.

[Amadis of Gaul]

Umm, sure... That otherwise excellent, type rated pilots apparently do not have a deep enough understanding of their machine's backup systems. You said, "complaint," sir, I did not. I'd call it a common concern. Sooner or later, that small, missing bit of functional detail will bite you.


I think you're somewhat mistaken in presuming that these sorts of questions are coming from "excellent pilots" typed in anything other than their keyboards. I, for one, rather doubt that had the OP actually been a crewmember on the aircraft in question, his next stop after talking to that apocryphal captain of his would have been PPRUNE.

But that's just me.

[Port Strobe]

So either switch will pop the RAT out, but only the ELEC will force the RAT Gen to power its respective systems. It looks like this is the reason for two switches; the RAT Gen takes priority over the systems it feeds.
So, having a HYD failure, pressing the HYD button will get the RAT out without force powering the RAT AC Gen. If you had a HYD failure and still had serviceable engine generators, but pressed the ELEC switch, you'd pop the RAT, still get hydraulics but you'd also force off the good engine generators (only on those bus bars the CSM/G supplies of course).

If you dispatch with APU GEN inop, and have an engine failure in flight, you're left with only one electrical source just after the failure has occurred. Should there be some form of electrical generation malfunction with the remaining electrical source, would you enter mechanical backup law whilst on batteries during the time taken as the RAT auto deploys and EMER GEN couples to the electrical network? Or would you remain in alternate law (gear up of course)?

If mechanical backup law is true, would there be a case for deploying the EMER GEN if you were reduced to a single electrical source in flight? An electrical malfunction at an ill timed moment could leave you in no man's land whilst the RAT deploys and generator is coupled. Would the EMER GEN just power the essential systems as per ELEC EMER CONFIG and leave the less essential systems to be powered by the remaining IDG? Or would it be more complex?

[Amadis of Gaul]

Port Strobe, I suppose the "big picture" answer to your question would be how likely would it be for the same airplane to suffer what amounts to three separate electrical failures within one flight (the APU gen is deferred, then both IDGs fail in sequence). The "no man's land" scenario you're describing would last approximately 8 seconds (I suppose those could be the longest 8 seconds of a pilot's life under the right circumstances), which is NOT long enough to justify flying around with the RAT deployed, in my view.

[itsresidualmate]

Port Stobe; I don't have time to go through the schematics and wiring manual right now, I'll have a look next week.

[Rocket3837]

Port Strobe (http://www.pprune.org/members/71880-port-strobe)


Aircraft will not go down to MECH B/UP in the scenario you described because enough HYD power & Electricals (by BATTs) are available. ALTN LAW will activate (with L/G up).

[vilas]

Port Strobe
Between failure of all electrical sources and deployment of EMER GEN via RAT takes 8 seconds and aircraft is powered by batteries through the inverter, it will go in alternate law with rudder mechanical till FAC 1 is reset, then rudder will also change to alternate. Mechanical back up will happen if there no electrics whatsoever or all computers trip together.

[Port Strobe]

Thanks all who answered, very helpful indeed. I agree it would be a highly unlikely scenario, however if someone had listed all QF32's ECAM procedures here 5 years ago they'd have been shot down. Now I've learned a bit more about mechanical backup I see it was unfounded, but thanks to those for helping.

[screwdriver]

WhyByFlyer
At last.!! Someone who knows...or has read, and understood, FCOM. Thanks for the input. :D

No Fly Zone
What on earth are you on about?:ugh: