Hi,

I'm not sure if this is the correct forum section for my question, but I couldnt find a better one. Please feel free to move this post to another section if necessary.

Thanks!

 

Can anyone please tell me from a technical point of view why the yellow hydraulic pump is used when the Nose Wheel Steering and Anti Skid switch is in off position?

Why is the hydraulic system switching from the green pump to the yellow pump in this case when using the brakes?

Thank you!

Best regards Andi

Edited March 12, 20206 yr by 737Andi

Why not  try  the  fslabs  forum  sure  you  will get a  answer   from Norman

2 hours ago, 737Andi said:

Hi,

I'm not sure if this is the correct forum section for my question, but I couldnt find a better one. Please feel free to move this post to another section if necessary.

Thanks!

 

Can anyone please tell me from a technical point of view why the yellow hydraulic pump is used when the Nose Wheel Steering and Anti Skid switch is in off position?

Why is the hydraulic system switching from the green pump to the yellow pump in this case when using the brakes?

Thank you!

Best regards Andi

 

Is this related to on ground with no engines running ? The yellow electric pump is used for alternative brakes and since the engines isnt running(green system) this is used.

NWS is on the green system (Neo is on the Yellow though i think) and can be powered on ground via the electric Yellow pump providing pressure via the PTU before any engine start. (also for normal brakes)

Yellow system also is used for cargo doors for instance

 

Michael Moe  

Edited March 12, 20206 yr by Michael Moe

3 hours ago, Michael Moe said:

Is this related to on ground with no engines running ?

Lets assume I have both engines running on ground. Then the yellow and green pump are active. Nevertheless as soon as I switch the NWS switch to off the yellow pump is responsible for braking. Whats the reason/explanation behind this? 

 

Quote

NWS is on the green system (Neo is on the Yellow though i think) and can be powered on ground via the electric Yellow pump providing pressure via the PTU before any engine start. (also for normal brakes)

If parking brake is set on on the ground the green system is not powered over the PTU when only Engine 2 is running. Only when parking brake is off the green system is powered over the PTU. If I start engine 1 the PTU deactivates itself as soon as 500PSI difference between green and yellow is undershot.

Edited March 12, 20206 yr by 737Andi

2 hours ago, 737Andi said:

Lets assume I have both engines running on ground. Then the yellow and green pump are active. Nevertheless as soon as I switch the NWS switch to off the yellow pump is responsible for braking. Whats the reason/explanation behind this? 

This is correct when the A/SKID & N/W STRG switch (to give it its full name) is OFF according to Airbus documentation (http://www.smartcockpit.com/docs/A320-Landing_Gear.pdf    page 7)

No reason appears to be given, but yellow is the alternate braking system and switches in automatically if the switch is ON and green pressure is too low.  So the switch may have a dual function in forcing use of the alternate system in case of a fault with the green system and the automatic changeover does not happen.

 

2 hours ago, 737Andi said:

If parking brake is set on on the ground the green system is not powered over the PTU when only Engine 2 is running. Only when parking brake is off the green system is powered over the PTU

 

Have a look at the logic diagram in page 1 of http://www.smartcockpit.com/docs/A320-Hydraulic.pdf ,  particularly that big OR gate near the bottom.

On the ground with only one engine running (L/G SHOCK ABS, BOTH OFF and BOTH ON signals not present), the PTU will only run if the parking brake is off (and the towing pins are not inserted, which I don't believe is modelled). 

Again no reason is given, but this stops the PTU running unnecessarily during a normal start sequence while still allowing it to run in the air with one engine out or during single-engine taxi.