A 320 Antiskid Nosewheel Sw off prior to push

[Magnetic Iron]

A question

Does your company SOP require that you switch the Nosewheel Off prior to pushback ? Whats the advantage of leaving the SW on during push, no
Our fleet has older Airbus and newer ones, it was easier to always switch the ASKID/NW off prior to push, no we check, I understand it is for what is written below.

NW STRG DISC........................................................ ...............................................CHECK AS RQRD
In case of pushback (conventional or towbarless), the nosewheel steering selector bypass pin must
be in the tow position. The ECAM ’s NW STRG DISC, or N WHEEL STEERG DISC memos indicate
this to the flight crew.



Could someone explain this further as what I have found in the FCOM is insufficient to understand this 100% ?

Also yes we have to check this below, if anyone has had problems with this and bypass pin faults ? It would be interesting to learn from your experience

CAUTION If NW STRG DISC is not displayed on the ECAM , but the ground crew confirms that the steering selector bypass pin is in the towing position, then the pushback must
not be performed. This is to avoid possible nose landing gear damage upon yellow
hydraulic pressurization.To dispatch the aircraft in such a case, Refer to MEL/MI-32-51 Nose Wheel SteeringControl System .

Thanks for your help, gentlemen

[aerobat77]

cannot speak explicit for the airbus, but on the bae146 nosewheelsteering has to be off during any pushback . if not and the hydraulic system is pressurized the hydraulics would try to counterreact when the tug starts to make a turn .

this could/would damage the actuators.

on the bae there was a pressure relief to prevent destroying the whole actuator in case the nw was forgotten to switch off. but when this relief was already pushed no hydraulic pressure will build up and you are without nosewheelsteering so it has to be ckecked.

i quess its similar to the airbus,

normally the pushback supervisor will ask to confirm hydraulics are off / nw off before they start the push.

cheers

[FLEXPWR]

Wrong guess,

Every aircraft is different, and on the A320, the person supervising the pushback must insert a pin in the NWS system on the nose gear leg. This de-activates the steering and associated hydraulics.

Switching off from the cockpit has no real meaning if the steering pin is inserted. Some airlines like to do it anyway in their SOP's, but I have seen no benefit.

However, it we be useful if the pushback supervisor lost its pin or if you are on a remote airport not used to push/tow this type of aircraft.

Of course it is useful to reset some BSCU glitches (carful with that, Airbus has very specific procedures in this regard).

[Dan Winterland]

Some older aircraft with an earlier standard of BSCU needed this to prevent damage to the NWS when the Green Hyd system powered up on engine 1 start. Later aircraft or those where the owners felt the need to cough up for the modification don't need the NWS off for pushback. Just follow the procedure in the manuals for your MSN and you will be correct.

[Cardinal]

For a time our procedure was to turn off the A/SKID NWS cockpit switch (unneccesarily) for every push, and for our efforts we had a number of problems with the switch. Thankfully our manuals now reflect reality.

[jtr]

As Dan Winterland said, it was to do with BSCU mod version. Some companies for the sake of simplicity made it compulsory across the fleet regardless of mod status, same as some treat the brake check, even though it is not required by bus on all a/c (cue airmanship debate)

[Dan Winterland]

Debate off and running: Indeed, about a third of our aircraft have the new hydraullic architechture and getting on a bit, I can't remember which do or don't. And by the time I get to start taxying, I may have forgotten if I did know! Obviously, my company knows there are people like me around, so we do a brake check on every aircraft.

[Magnetic Iron]

Like Dan we have older and newer A 320

i feel that it showed always be switched off for standardization, whats the advantage of leaving it on?

Now we have to switch the the NW STRNG off on the old 320's and leave it on on the new ones.

How do you know when to switch it off , when there is no ANTI SKID .NW memo

When you change to the old ones that require it to be turned off, how can you tell from the Ecam memo.
Am I missing something here ?

yes when the pin is disconnected the NW STRNG is in the memo and green.

The QRH says check as required and the FCOM explanation for me is inadequate.


We used to always switch it off and now we have to "check as required" , annoying

thanks for your input

Thanks

[Rick777]

When I was flying the 320 we turned it off even though the NW cutout pin was also always in. Disadvantages are extra wear on the switch and forgetting to turn it back on before taxi.

[bazb]

The nose-wheel steering issue on the A320 family (and also the A330/A340) was a hardware problem, not a software one - although the software was upgraded on a relatively regular basis. The problem was contamination (water, de-icing fluid etc.) entering the nose wheel steering box, causing electrical malfunctions and it took Airbus several attempts before they managed to produce an acceptable design with effective sealing. During that time it became SOP to switch off the nose-wheel steering (NWS) before push-back pre-empting any issues with the NWS becoming active during the push-back, even with the steering pin engaged. Once the issue had been resolved - and it took several years for Airbus to produce the final solution - most airlines had an SOP to switch off the NWS before push-back until all their aircraft had a modified box. This makes sense in that it meant crews did not have to be aware of the mod. state of the aircraft. Once all the aircraft in the fleet were modified it then became acceptable to no longer switch off the NWS before pushback.

[Beeline]

Rubbish,

If the box (5GC if I remember rightly) goes U/S, Hydraulic pressure is ported to the servo valve and equally to the actuators.

The switch in the flight deck 'A/skid NWS off' is a soft reset/inhibition for the BSCU hence you get no BSCU functions (Steering inputs or Anti skid).

Therefore you always need the pin in and the towing lever to Tow to prevent over stressing the actuators, a plethora of subsequent inspections are required, including strip down of the actuators if the box fails under tow. Makes sense that in total electrical failure the wheels are centred by hydraulic lock when compressed.

If is there is a short caused by moisture ingress a NWS Fault will present itself on ECAM regardless of tow lever position. No dispatch

The only way of not allowing hyd px to the servo valve on classic aircraft is dropping the NLG Doors. As they were on the Green system door up return line.

[T.R Haychemu]

BazB is right.

I wasn't so much a case of contamination causing the electrical box (indeed 5GC) to fail causing the Wheel N/W STRG Fault ECAM caution.
It was more that on occasion (and without failure message), when the lever was moved and pinned to TOW the microswitch did not function electrically.

As the engines were then started on pushback and hydraulic pressure became available, the NWS would center and break the shear pins in the tow bar.

TFU 32.51.12.005 refers to both issues with the 5GC Electrical Box, both the N/W STRG Fault Ecam and the pressurisations during towing operations.

[Beeline]

So he wasn't right then.

I can't see the TFU but I doubt it has flight crew recommendations for SOPs.

How does the NWS/Antiskid Switch off effect 5GC then, it doesn't just any form of MSG. It only prevents inadvertent inputs from pedals or tiller. Another issue.

If the micro switch fails you get powered actuators. Fail safe to null. I have stripped down many a steering cylinder!!

If you are towing without hydraulic pressure as you are suggesting you require a tow-bar-less tractor or Shear pin-less tow bar. An engine start on stand should be conducted to confirm adequate brake pressure if elec pump u/s and on a shear type tow bar.
(off point, sorry)

[T.R Haychemu]

The TFU and also TFU 32.51.12.004 have referenced changes to FCOM/SOP 3.03.07 with Temp Revision 746/846 for pushback procedures, asking for the NWS/Antiskid to be selected off prior to pushback.

There was then an SB/Mod for the box 5GC for improved sealing, and then this TR for the FCOM/SOPs was removed.

Which is what the OP was asking about I believe, what were the advantages of having this SOP to have the NWS/Antiskid selected off for pushback.

So as BazB pointed out, due to the issue of 5GC failing to provide the BSCU with the ground that informs it the tow-pin is inserted, the advantage is, that if 5GC doesn't provide the signal, having the NWS/Antiskid switch in the off position will stop the nosewheels trying to centre (and breaking towbar shear pins), as the hydraulic pressure rises during engine start & pushback.

If the 5GC microwitch fails, it doesn't "fail safe" to anything, it will be simply a pushback as if the tow-pin was never inserted in the first place! :)

[Young Paul]

Yep, it's nothing to do with belt and braces. It was a specific technical issue which meant that the cutout pin didn't. I've been flying Airbus 320s for about 12 years, and I can just remember when the requirement to switch off NWS prior to pushback was introduced. The ones I was operating were modified so this wasn't necessary about 7 or 8 years ago, I believe.