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Old 31st Dec 2007, 17:25   #61 (permalink)
 
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Just stick to the last ? (question mark)
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Old 31st Dec 2007, 17:36   #62 (permalink)
PBL
 
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Hetfield,

you are quite welcome to misunderstand what I say, build straw men and shoot them down, not answer my questions, anything you want.

PBL
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Old 31st Dec 2007, 17:40   #63 (permalink)
 
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PBL, the PTU transfers hydraulic pressure (via shaft power) between the G and Y systems. There's no fluid transfer.

IIRC, PTU logic is based on p/b, the delta p between G and Y being >500psi and a few other things mainly related to engine start, cargo door operation, flt etc. Reservoir low quantity plays no part, so if either the G or Y system has a leak the PTU will start once the pressure in the leaking system is below 2500PSI and won't stop until the PTU p/b is pressed.
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Old 31st Dec 2007, 17:57   #64 (permalink)
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Quote:
Originally Posted by violator
PBL, the PTU transfers hydraulic pressure (via shaft power) between the G and Y systems. There's no fluid transfer.
I think you might find there is actually some path whereby fluid might pass between G and Y or vice versa. And certainly if there is low or no fluid in the G system, there has been a transfer of fluid from G to somewhere. Where?

I could probably carry on all day like this, but I am not interested in playing language games. I was hoping that somebody who knew of a specific scenario might care to share it here.

PBL
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Old 31st Dec 2007, 17:59   #65 (permalink)
 
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It's not a language game at all.

BTW I'm very dissapointed about your system knowledge.

@Giggey

Obviously you asked a very good question. Maybe exceeding some scientists cababilities and making some drivers to have a look in the manuals.

Happy New Year
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Old 31st Dec 2007, 19:37   #66 (permalink)
 
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hetfield
Quote:
Leave the hydraulic systems on, don't touch stick and rudder, use eng thrust to try it in the sim.
Wouldn't work, mate.. the FBW system compensates for thrust changes and keeps you the right way up - even with one at TOGA and one at Idle. Failing all three hydraulic systems might at least give some spoiler or aileron upfloat to make it interesting..
TP
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Old 31st Dec 2007, 21:38   #67 (permalink)
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Quote:
Originally Posted by hetfield
BTW I'm very dissapointed about your system knowledge.
If you look a little more closely, you will find that I have given you no information about my system knowledge at all.

.................... I am here because I had hoped that on this forum of experienced aviators there might be some people who could tell me things I don't know, and some who might like to learn things which I could tell them.

[Edit: material on the discomfort I feel with what is, to me, the often puerile level of interaction on this forum, that I am surprised to find coming from people who self-describe as technical professionals.]

Hetfield, despite your reticence, I would still be grateful if you would share with me your personal knowledge of how both primary A320 hydraulic systems fail together in line service.

PBL

Last edited by PBL; 1st Jan 2008 at 09:11. Reason: A somewhat lengthy description of problems and plea for different kinds of interaction has timed out
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Old 1st Jan 2008, 01:54   #68 (permalink)
idg
 
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I have not read the entire thread so apologies if I am covering what has already been said but...

Airbus have warned of a situation that could indeed lead to a 'Dual HYD Failure'. The circumstances were a leak in the Green system after start that was not picked up all the way to Take-Off. On T/O the leak rate increased and total GRN system loss ensued but the warnings are inhibited because of flight phase. As has been pointed out before, the Yellow system began to drive the PTU, but with no fluid to drive in the GRN system it spins at an almighty rate and very quickly overheats the Yellow system. The aircraft now climbs above 1500' and lo and behold a Green system failure and Yellow 'Failure'! Of course the Ylw is actually an overheat that could be reinstated once cooled, but from memory the crew didn't bother with that they just went straight back to land.

In similar circumstances once the Ylw fluid had cooled and the PTU selected off the yellow could have been re-instated.

Oh yes another thing...

An Airbus rep told me of instances of Green to Yellow transfer but it is not 'intentional'. It occurs in the brake shuttle valves (Green / Yellow system) perhaps when seals fail internally? Sorry can't remember the exact details now.
Happy New Year to all.
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Old 1st Jan 2008, 07:07   #69 (permalink)
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Quote:
Originally Posted by idg
An Airbus rep told me of instances of Green to Yellow transfer but it is not 'intentional'
Thank you, idg. I wonder whether he was talking about known instances, or merely about what he knows about the hazard analysis in the certification basis?

Let me give some indication for those who might be interested but do not know, how a hazard analyst might go about analysing such systems.

First, heshe might look at the crude system diagram in 1.29 and observe that there are at least two devices which connect between the G and Y hydraulic systems. (idg is reporting a third, which I don't believe is indicated in those diagrams, but I can't be bothered to go check.) Now, for each of those devices the certification basis for the AC will include documents, amongst them one assigning the level of criticality of the device, and another giving an argument in detail as to how the device satisfies the assigned level of criticality.

Now, I don't know the detailed design of those devices; I have never seen such engineering documents. And I doubt anybody else here who is willing to say something has either, because those documents are prima facie proprietary and the people seeing them form an restricted group bound by non-disclosure agreement, and nobody who takes their code of practice seriously (i.e. all engineers except for the occasional crackpot) is going to violate non-disclosure for the sake of some guy asking questions on an anonymous web forum, unless there is something seriously, seriously wrong (which I doubt).

So my question to violator was a "leading question". In other words I already know that (as a hazard analyst interprets these words) there are paths between G & Y through which fluid can theoretically travel. Any, say, HAZOP-like analysis will explicitly consider such a scenario and its consequences, but as I said I do not know what techniques are used in the certification basis.

Now, I have never seen any hazard analysis on any piece of complex equipment which was completely correct, without exception. It may be beyond the bounds of current human capability to devise one for such a thing as a commercial aircraft that was exceptionlessly correct. Most of them have faults. Some of them, occasionally, have glaring holes. And I know, for certain specific aircraft that interest us, that there are hazards whose severity (technical term) is catastrophic (also a technical term) that have not been mitigated, because we have reverse-engineered and identified them.

I thank idg also for explaining the PTU-overheat scenario in a little more detail. My next question if I were to follow that line would be of course what the consequences are of that abnormal state that the PTU gets into, but as I said, I doubt anybody here with either the detailed engineering design or the certification basis documentation sitting in front of himher would be inclined to answer.

Sorry for the length of this note. I'm just trying another writing technique to try to avoid this pointless, and to my mind rather silly, one-sentence repartee. I do hope I can get back to brevity; I'd rather just ask a simple question and hope for a sensible answer.

PBL
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Old 1st Jan 2008, 07:39   #70 (permalink)
 
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@TyroPicard

HAPPY NEW YEAR

You were a little faster than me and absolutely correct about simulating a total HYD loss 320 family in the SIM. Like you said the Flight Control Logic is still aktiv.

Sorry for that.

Did it in the A300 SIM and there it works, cause switching all pumps off screws the SIM up.

@idg

Yes, fully correct. Beside that scanario there have been incidents of DUAL LOSS due to PB failures. The crew handled the situation very well, but the PTU PB even switched to OFF kept the PTU running.

Last edited by hetfield; 1st Jan 2008 at 07:58.
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Old 1st Jan 2008, 09:02   #71 (permalink)
 
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Quote:
Originally Posted by PBL #53
There are obviously people here who don't know what such calculations can say and what they can't, and I don't see how to give a feel for this which can be packed into a dozen words.
Replace "such calculations" with "FCOM"
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Old 1st Jan 2008, 09:16   #72 (permalink)
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IFixPlanes,

well, there are obviously people here who don't know the FCOM in detail either. But what has this issue to do with knowing or not knowing the FCOM? As people have pointed out, losing three hydraulic systems is not considered operationally.

PBL
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Old 2nd Jan 2008, 16:47   #73 (permalink)
 
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@IFixPlanes

Thx for your input

This thread has shown clearly that also a scientist should take a look to the system description before talking .
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Old 2nd Jan 2008, 22:25   #74 (permalink)
 
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Quote:
An Airbus rep told me of instances of Green to Yellow transfer but it is not 'intentional'. It occurs in the brake shuttle valves (Green / Yellow system) perhaps when seals fail internally? Sorry can't remember the exact details now.
It is my understanding that this would only occur when the brakes are applied or pressure is sent to the shuttle valve from the Brake control unit. Normally not pressurised. Transfer would stop when brake pressure released.

Also, I'm not sure if the brake hydraulic fuses are before or after the shuttle valves. It's been a while. If they are before they will stop the flow when it gets beyond a normal rate.

In regards to the green system loss. If the warning is inhibited due to flight phase screening to 1500'. The plane does not fly around long below 1500' agl. (maybe a pilot type might tell us how long from takeoff to 1500') I'm tipping it's not long.

Your yellow system might get to an overheat but it still takes time. Depending of course on the amount of work it does in the PTU and other controls. It also depends on the rate of loss of fluid from the green system. It's generally going to keep tyring to make pressure until the reservoir is empty. A small leak will take some time to dissipate the fluid. The Engine pump will continue to make pressure though. The PTU will not come into play.
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Old 3rd Jan 2008, 00:07   #75 (permalink)
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Is there not a flow restrictor fitted to the PTU to limit the maximum RPM? What would generate more heat, the flow a fluid through the motor side of the PTU or the friction in the dry pump side?
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Old 3rd Jan 2008, 07:30   #76 (permalink)
 
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@Toqueman

I know personaly about an incident where G Loss occured during TO run and due to ECAM logic warning was was inhibited until 1.500. Immediatly thereafter Y SYS OVHT. This means about 3 minutes.
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Old 3rd Jan 2008, 13:00   #77 (permalink)
idg
 
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The Airbus warning was from an actual event when the 'dual failure' occurred. I'll try and get some more info but it actually happened, and happened quickly enough to be present when the a/c climbed above 1500'. Probably about 1min 30 secs.

I'll also try and get a tech diagram of the shuttle valve.
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Old 3rd Jan 2008, 15:20   #78 (permalink)
 
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Quote:
Originally Posted by idg
...An Airbus rep told me of instances of Green to Yellow transfer but it is not 'intentional'. It occurs in the brake shuttle valves (Green / Yellow system) perhaps when seals fail internally? Sorry can't remember the exact details now.
A so called "brake shuttle valves" between green and yellow system does not exist in the A320 braking system.
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Old 3rd Jan 2008, 15:29   #79 (permalink)
 
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Last G+Y loss scenario which I know hapens at BA PRG-LHR (A320-100)flight one or two months ago.. Succesfull landing at PRG with full emergecy, one tyre blown-out due temperature. Airbus solution is inhibiton PTU operation below 1500´, probably on new planes only...

Last edited by františek dobrota; 3rd Jan 2008 at 18:41.
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Old 4th Jan 2008, 06:37   #80 (permalink)
idg
 
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IFP

Well my manuals talk of 'Dual Shuttle Valves' so I assume Airbus know they exist! However your inference that I'm barking up the wrong 'valve tree' is correct !!

The valve that has had most problems in this area is the Parking Brake Operated Valve.

I have a magnificent diagram with cross sections of all the valves but no way of posting it!

Will PM to anyone that requests it!
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