Why yellow in stead of green Hyd. with ''new'' A320 NWS?

[Pander216]

Hi Gents,

Does anyone know the reason why airbus switched the nosewheel steering from green hydraulics to yellow hydraulics in the new series of A 319/320/321's?


Cheers!

[FlapsOne]

Probably just to share the load more evenly. Also allows the NWS to work with the yellow elec pump in use as per one engine taxi and maybe saves some overloading of the green system.

Just guesswork I'm afraid.

[Watchdog]

or...how about for use with the main gear pushback tugs - with the elec yellow pump you can steer without an engine turning

[Pander216]

That makes very well sense! Never used one though, so i hadn't crossed my mind before. Thanks for the help!

cheers!

[CleanSpeed]

So that you don't lose normal brakes and NWS in the event of a green hydraulic failure.

[Pander216]

If you lose green hydraulics in the old A320's you put the A/SKID NWS switch of and thus switch to alternate braking (yellow hyd.). With the new system if you lose yellow hydraulics you lose NWS and will have normal braking. So with the new system you only save one setting you have to make, or am I missing something here?

[FlapsOne]

I'm not too sure you are comparing like with like.

I'm no expert on the old system (or the new one really) but with the newer system an Alternate Control Braking Unit (ABCU) using the Ylo system comes into action, if Grn Hyds Px is insufficient, and provides Alt braking with Anti skid.

If the anti skid is inop (switched off or various Y and or G hyd faults) then you get alt brakes without anti skid using Ylo px (if available) or the accumulators which are automatically limited to 1000psi application pressure.

If you've got access, FCOM 1.32.30 summarises it quite well (for a change!).

[Pander216]

Apparently overlooked it when browsing FCOM this morning at 04:00 Z enroute to Malaga

Cheers guys!

[eire757]

Originally Posted by Watchdog

or...how about for use with the main gear pushback tugs - with the elec yellow pump you can steer without an engine turning

Will this work? As you know the A320 tiller wont move the nosewheel unless you are moving even if you do have hydraulics. Does this include moving BACKWARDS on a power-push? Personally I have never had to try it out.

[aidey_f]

When did this happen?

Just out of interest, anyone know when the switch happened? MSN would probably be too much to ask...

[Swedish Steve]

Originally Posted by eire757

Will this work? As you know the A320 tiller wont move the nosewheel unless you are moving even if you do have hydraulics. Does this include moving BACKWARDS on a power-push? Personally I have never had to try it out.

Now you confused me. I am sure that last time I had a steering problem I moved the nose gear with the tiller while parked on the gate(with the lock out pin removed). When does moving come into it?

[aintsaying]

Watchdog has got it.
When you are using the remote control MLG pushback machine(one man push back) you need the engine running for steering or you now have the new system which allows you to have the electric hyd pump running.
I guess many customers have been asking for this and airbus has finally done something about it. (well a few years ago now.)

[mcdhu]

Probably a combination of reasons, but it was put to me that it was so that when the gear was lowered manually - for whatever reason - you didn't lose the nosewheel steering.

As to when it happened, it must have been around 2003.

Cheers,
mcdhu

[smudgethecat]

Originally Posted by eire757

Will this work? As you know the A320 tiller wont move the nosewheel unless you are moving even if you do have hydraulics. Does this include moving BACKWARDS on a power-push? Personally I have never had to try it out.

Its not movement that is required, its an oil pressure signal(engine running) that enables the NWS

[glhcarl]

I could not control myself any longer, I had to provide to the following comment:

I have never seen GREEN and YELLOW hydraulics. The hydraulics I have worked with have all been RED or PURPLE!

[aintsaying]

Yep, thats right too.
On the A320 the Hydraulic fluid is purple for the Green, Yellow and Blue systems.

[A319CJ]

Hi Pander216

The one of the reasons for this modification, is that you can now steer the nose wheel after a gravity (free fall) extension.
reason:
On the pre mod. system the steering servo is supplied from the landing gear door closing line (Green HYD)
On the post mod. system the steering servo is supplied from the Cargo door supply line. (Yellow HYD)

Doing a gravity extension the hydraulic supply is isolated and vented to prevent hydraulic locks, the gears and doors uplocks are released.

too Swedish Steve

nose wheel steering is only allowed if the following are met:
- Towing lever in normal position
- one engine in operation "master sw one" (pre mod)
- A/C speed lower then 130kts
- Main gear compressed

[Watchdog]

reading the FCOM applicable to the 'new' system, I note that one still needs an engine running to get NWS. In the 'old' ones we had always to start #2 first with the power-push - now it doesn't matter of course. That could be another reason.

eire757... to your question - yes - my experience with the 'single operator' tractor thingy was positive - smoother pushback that the towbar arrangement, and I can make smoother steering inputs than the conventional setup.