PPRuNe Forums - Virtual A320 Triple Hydraulic failure

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- - Virtual A320 Triple Hydraulic failure (https://www.pprune.org/tech-log/306033-virtual-a320-triple-hydraulic-failure.html)

I know hat a "Dual Shuttle Valves" exists, but you have mentioned a "brake shuttle valves" whitch is connected to green and yellow hydraulic.
For Images simply use : :ok:
ImageShack® - Online Photo and Video Hosting
The "Parking Brake Operated Valve" is not so complex:
http://imageshack.us/a/img186/8226/p...dvaljq2.th.jpg
Parking/Ultimate Emergency Braking - Schematic:
http://imageshack.us/a/img186/1479/p...gencht8.th.jpg

concerning the fluid transfer bit

Hi All
Forgive my ignorance, But unlike the 737 classic series which can allow fluid transfer depending on which system you use to apply the parkbrake and which system is running when you release the park brake. I was under the impression that the A320 use of yellow and green hydraulic systems to the brakes were completly seperate systems with no possibility of fluid transfer, right down to two seperate supply lines to the brakes, and operating seperate pistons. If someone can explain it to me about the A320, i would aprecciate it.

Sorry if I haven't made my query clear, its my first post

You are correct! Think of the parking brake handle as a "green system" enable, when parking brake released, it then allows green system pressure.

Quote:

Originally Posted by elfinknight

I was under the impression that the A320 use of yellow and green hydraulic systems to the brakes were completly seperate systems with no possibility of fluid transfer, right down to two seperate supply lines to the brakes, and operating seperate pistons.

It seems from the history of this thread that the interpretation of the word "possibility" depends on whether you are a pilot or engineer considering the normal operation of the systems or whether you are a systems safety analyst considering what can go wrong.

They don't transfer fluid during normal operation. However, there appear to be ways to get cross leaks that involve something not doing what it should do.

PBL

Hidden Trust about the A320 G Hyd System

This is what I read in a website (http://wisdomseva.com/ghyds.html) created by an Indian Airlines Captain:

Quote:

DESIGN DEFICIENCY IN A320 ‘ GREEN ’ HYDRAULIC SYSTEM

Some time back, I used to notice the Green Hydraulic System indication of the A320 showing decrement during flight at higher altitudes with time, comparing to the Yellow & Blue system. My wonde for the reason compelled me to accomplish in-depth study of the entire Hydraulic system of the A320 a/c as something inside me, within, was inspiring me to do so, telling me that there is something wrong. I made several workshop / hangar visits, studied the system layout, circuit diagrams and various Maintenance Manuals involving lot of tedious effort & time.
Ultimately, the truth revealed by itself. I found, ( unlike the other two systems ), the Green Hydraulic System Reservoir and its associated circuit so located by design that when it gets subjected to cold- soak, the hydraulic fluid contracts to such an extent that would trigger a SYS LO LVL thereby causing lot of problems for the ignorant pilot. I took up the matter with the DGCA/IAL authorities but my theory was rejected & all efforts were in vain.

My belief was firm, something within me inspired me to go ahead & stop not till the goal is reached. I approached the Airbus Industrie with the problem alongwith all the papers, drawings & my hard-work. The AB carried out detailed investigations / flight tests. This is what was their finding :
Quote : “ After several reviews with different Airbus resources involved in definition and design of the A320 hydraulic and landing gear system we came to the following conclusion :
It has been confirmed that assuming the very specific case of a flight proceeded with abnormal L/G door Config ( Partially or fully open ) in high altitude, it leads to an cold soak effect on the green Hydraulic system that may be followed by the triggering of the ECAM LO LVL warning. Applying the ECAM procedure will lead to a loss of the green hydraulic system.
The loss of the green hydraulic system is considered as major, whereby the a/c is flying in normal law and apart from landing gear gravity extension and multiplying the landing distance per 1.1, no specific crew action is required. When during decent when the cold soak effect disappears, the fluid quantity indication on the system page may return back to normal and when monitored by the flight crew, the lost system could be recovered.”

Unquote : I also gave them the modification proposals in regard to the design in their circuit to overcome this problem which they also accepted. But stated that the expenditure involved was not feasible / due low probability etc.and to let things continue as it is. They also regretted the delay in reply as a number of Airbus departments were involved in the investigation.

What the Airbus gave me in return for my hard work :
‘ THANK YOU FOR YOUR INPUTS ’, Yes, just these five words.

Any takes on this one?

I generally fly with the gear doors closed myself, interesting information for what it's worth. :D

Well he further states in the article

Quote:

During the external pre-flight walk-around we do before each flight, it is very important to ensure the rubber sealing at the wing-root , wheel-well area etc are all well secure /intact / not worn out etc. or in case if there is partial door open during flight as ambient cold air entering the Main Wheel bay could lead to erroneous indication.

I guess this would be the case for 15 odd years old aircraft. I guess I do not have to worry about it as our fleet is virtually brand new :)

Well, to keep this thread creep going, has this scenario happened to anyone? I don't really think it's a big one to worry about, all bus pilots are pretty watchful of hydraulic "Faults" to return to the normal condition, losing the GREEN system is a serious problem but easily managed.

Thanks PBL for your reply
I'm a mechanic on 737 classics most of the time with very little experience on the A320s.hence my query

if you loose G B and Y system on the 320, I assume that as the plane is in a negative equilibrium without his 6-7 computers(ELAC,SEC & FAC);
without hydro, his computers wouldn't be able to keep the plane straight and level, resulting in an engage spiral drive until destruction due to high G)...

Well, at my last check we had a bit of a play with the 'Sioux City' scenario.

Interestingly the aircraft was remarkably flyable with thrust only. Dependant on weight we had an N1 thrust setting (setting the N1 mode helps a little with the Ecam engine indications) of about 'datum 45%'. Applying thrust brought the nose up and decreasing, obviously, dropped the nose. Speed control was attainable using this and turns were achieved using differential thrust.

To sum the whole thing up, as a team, we managed to get the aircraft back to the airfield and achieved a landing, albeit some what 'heavy' but certainly walk away from.

Can it happen? Well anything can happen and an aircraft had a double hydraulic failure during takeoff due to a failure of one system and an overheat of the second system by the PTU. All it needs then is a leak in the third and you are in big trouble!

Enjoy

@wobble

Is your sim programmed for a no HYD scanario?

Mine isn't.:bored:

The setup was for a triple hydraulic leak resulting in the requested failure.

First the Green, then the yellow then the blue.

Quite easy to do.

Quote:

First the Green, then the yellow then the blue.

Quite easy to do.

Yeah, concerning system behaviour, it's easy indeed.

What about an aerodynamic modell in your Sim with total loss of flight controls ?

Having never, obviously, been in that scenario for real I cannot judge the sims modelling.

It felt very real. An extremely light touch is required on the thrust levers and a datum power to give speed stable flight with an 'acceptable' rate of descent needs to be found. That is all weather/weight dependent etc.

Once that datum has been established the aircraft can be 'steered' using aysemetric thrust and climbed and descended using thrust. It gets out of hand and therefore control very quickly though.

We managed to establish ourselves on a rough 'airfield' finals with 800fpm ROD descent and speed stable. That, our simulator thought, was acceptable for a rather heavy but survivable landing. Thoroughly recommend having a go if you get the time as it is an excellent handling/communication exercise if nothing else.

Quote:

What about an aerodynamic modell in your Sim with total loss of flight controls ?

That is in theory the easy bit. If the sim has been qualified to the relevant standards then the flight model accuracy will have been checked, and whether the controls are moving or not shouldn't be an issue. I might have some doubts about very long period motion, since most sim checks are on a 30second scale or so, but frankly that applies to the normal configuration too.

I'd be much more wary of the system simulation, personally. It's much harder to get that right for the sim builder, because they are usually working with just technical descriptions for any simulated kit, and dependent on ICDs for any stimulated stuff. Are you sure there wasn't some part of the system working that shouldn't have been. Do the unpowered controls lock or float? Which did they do in the sim? And so on.

[translation ... a sim is a computer .... not an aeroplane]

Whilst I agree completely with what MFS and JT have said about the authenticity of the sim modelling, I too have tried the triple hydraulic failure in the sim and it is really quite flyable.

Airbus TPs who have flown our sim, and have had the chance to fly this in the a/c for real, said that the modelling is pretty good. There might be upfloat on the ailerons and spoilers with total hydraulic loss but it would depend on the failure mode and where the control surfaces were at the time of failure. From memory our sim gives aileron upfloat.

As W2P has said the 'Sioux City' scenario is a little more tricky but still flyable once the datums have been established.

The reality is that the redundancy built into the system is such that, while a triple hydraulic failure is of course possible, it is statistically very unlikely. The flight control computers all going off line at once ( or being unable to work due to the appropriate system loss) is also very unlikely and the a/c was always intended to be flown with rudder and stabiliser control available until a FCC was reset.

During very early flight test I understand that the a/c was indeed flown to landing on stabiliser and rudder alone, and while the aircraft hasn't read the FCOM, I still feel that any exposure to the worst case scenarios is of benefit and would at least give one a fighting chance of adopting the correct technique even if the numbers were slightly off.

Triple hydraulic loss.

The A380 has a unique way of reducing the odds of a triple hyd loss-- there is only 2 engine driven hydraulic systems with the backup provided by electro-hydrostatic actuators and electrical backup hydraulic actuators. The latter 2 backup sytems have their own electrical motors and independant hydraulic fluid source which is refilled on the ground via the Green and Yellow systems. Seems like full proof when you consider that the systems are independant of each other. The primary reason for such a design is to save weight.:ok:

Just a personal curiosity to wake up this old thread.

In case of total hyd loss, do flight surfaces lock in place or they will freefloat into wind?

As far as I know, being a FBW (irreversible) flight control system, they are not mass-balanced. In that case, they might be prone to flutter.. just asking, don't know.