Deactivating HYD SYS A for pushback

[Mats_J 2]

If they are not using the lockout pin then is it to the Pilot In Command to switch OFF hydraulic A switches (ELEC and EDP switches).

So how is this communicated in RW? Sounds like an area prone for mistakes and mishaps. If I was ground crew I would always insert the pins whether HYD A is OFF or ON. Cheers,

[Flexman 30]

If they are not using the lockout pin then is it to the Pilot In Command to switch OFF hydraulic A switches (ELEC and EDP switches).And for the APU, yes it's not necessart to switch ON the Fuel pumps. But it's better for the APU performance to switch the fuel pump(s) ON.

Ok then everything makes sense. Also, refresh my memory on something please. I remember something about a 1 minute cooldown for a system I can't rember. Could it be that one pump remained on for 1 minutes after shut down for off-load cooling? I really cant remember anything else... just "one minute cooldown". I know the pumps' refrigeration fluid is the fuel itself, am I right?

So how is this communicated in RW? Sounds like an area prone for mistakes and mishaps. If I was ground crew I would always insert the pins whether HYD A is OFF or ON. Cheers,

I think it works both ways. Ground staff will always use the pin, and tech crew will always keep no pressure in A until they have a visual of the pin.

[davierosoft 13]

The èreferred way is to use all precautions, bypass pin AND A pumps off. The reason is human factor. Someone can miss to install the pin, someone can switch the steering on alternate for example. The danger in failing to deactivate steering could cause damage to the steering components, its not a problem of the tractor, the steering will break if hydraulics locks it.737 classic uses an hydraulic heat excanger inside the fuel tank to cool the hydraulic fluid. It is adviced to not use hydraulics when fuel is less than 760Kg in each wing. I must check on NGs.

[Hdarkace 2]

I think the cool-down period is for the APU and when you should turn on APU bleed air. shouldnt you wait 1 min before using APU bleed air?

[davierosoft 13]

1 mnute is needed to let stabilize all APU components, to warm them up at the right working temperature. The cooldown of the apu is done automatically.

[windshearDK 52]

I wrote the question based on the bulletin written in the normal crew flow in the FCOM.There it was advised that you turn off "hyd sys A" as the turning of the nose gear could damage it, if sys a was active. I did a successful push and start with sys a on and off, so I do not know which is the correct procedure. My question arose, because the manual simply refers to "sys A", and not sys A elec or eng. Does this help?

[Flexman 30]

I wrote the question based on the bulletin written in the normal crew flow in the FCOM.There it was advised that you turn off "hyd sys A" as the turning of the nose gear could damage it, if sys a was active. I did a successful push and start with sys a on and off, so I do not know which is the correct procedure. My question arose, because the manual simply refers to "sys A", and not sys A elec or eng. Does this help?

Both pumps off, ELEC and ENG. Check the schematics of what each does (pretty much the same: Pressurize HYD A)

The cooldown of the apu is done automatically.

I remember that from the 777.

[davierosoft 13]

Simply when a manual tells to turn off a system, such as an HYD system, the pressure in that system must be 0. Look at the indications. Both EMDP and EDP provide pressure for the same system, so the logic is: turn both off, or if I am sure that engine will not run untill push is finished, I turn off only the ELEC (and confirm with the pressure indication that pressure is 0)

[Flexman 30]

Simply when a manual tells to turn off a system, such as an HYD system, the pressure in that system must be 0. Look at the indications. Both EMDP and EDP provide pressure for the same system, so the logic is: turn both off, or if I am sure that engine will not run untill push is finished, I turn off only the ELEC (and confirm with the pressure indication that pressure is 0)

If the pressure was 0 we'd all be a little dead...

[davierosoft 13]

Not absolute pressure, but hyd sys relative pressure as seen on the gauges.The hyd pressure will be around 30/45 psi as the system is pre-pressurized to prevent pump cavitation. Air to do it comes from the bleeds.737 can fly w/out hyd pressure, only the rudder needs a stby system as it is fully hydraulic.On the last test I did the Stby rudder is not correctly simulated as the rudder didn't move with flight controls in STBY RUD position and no hyd system pressurized. Also other flight controls won't work. The only flight control surfaces moving with stby system are the LE devices. Must check for reverser stby operation.