Deactivating HYD SYS A for pushback

[windshearDK 52]

Quick question, the manual recommends turning off system A to prevent damage to the nose gear on pushback.My question is, if this is recommended for both the electronic and engine driven hydraulic pumps? Oh by the way, I love love love love the NGX!!!

[ExNusquam 11]

Yes, you turn off both so you can start both engines while pushing. Although, IIRC some airlines simply pull the nose gear steering pin which disconnects the hydraulic system from NWS, so they just pressurize both systems before push.

[RYR738 9]

edit !!

[trisager 2]

Quick question, the manual recommends turning off system A to prevent damage to the nose gear on pushback.My question is, if this is recommended for both the electronic and engine driven hydraulic pumps?

If you are starting both engines on the pushback, then yes - both A pumps off.

[windshearDK 52]

My initial thought was: Of course only the "elec hyd", but then I thought, hey I am starting the engines on push...!! Ok will deactivate both the alpha elec and eng driven pumps

[Flexman 30]

My initial thought was: Of course only the "elec hyd", but then I thought, hey I am starting the engines on push...!! Ok will deactivate both the alpha elec and eng driven pumps

The reason being that nose wheel steering is actuated by HYD A. If there's pressure in the system, some pushback trucks wouldn't be able to steer the airplane. So, both pumps for HYD A off.

[windshearDK 52]

Yeah I get that, but does that mean all of the alpha system? I guess it does then...?

[ajacied551 1]

It's not neseccary to switch OFF Hyd A for pushback when the nose gear steering lockout pin is installed (see FCOM 1 page NP.21.30) and most pushback drivers install's this pin during pushback. On the nose gear there is a lockout lever to block hyd A pressure to the steering actuator during pushback.

[StewCal 12]

It's not neseccary to switch OFF Hyd A for pushback when the nose gear steering lockout pin is installed (see FCOM 1 page NP.21.30) and most pushback drivers install's this pin during pushback. On the nose gear there is a lockout lever to block hyd A pressure to the steering actuator during pushback.

Correct...B pumps off was required in the 100 and 200 series...from 300 series on bypass pins are used....

[Flexman 30]

There isn't such thing as not all of the A system. It's either pressurized or not. There are more complex situations but, on normal operation, it's either presurized or not pressurized.You have to turn off both sources of pressure for HYD A. Otherwise, as soon as engine 1 starts, the engine driven pump will presurize the system. If on alternate nose wheel steering, then then nose wheel steering is actuated by HYD B.

[ajacied551 1]

There isn't such thing as not all of the A system. It's either pressurized or not. There are more complex situations but, on normal operation, it's either presurized or not pressurized.You have to turn off both sources of pressure for HYD A. Otherwise, as soon as engine 1 starts, the engine driven pump will presurize the system. If on alternate nose wheel steering, then then nose wheel steering is actuated by HYD B.

The Hydraulic System's is during pushback normally pressurized, Before the pushback driver start's with the pushback he install a lockout pin in the Nose Gear steering Lockout lever, This Lockout lever is pulled to block the Hydraulic pressure from Hyd A to the Steering actuator, Hyd B pressure is normally not used for steering. Alternate nose wheel steering is not automatic you need to switch it over with the Nose Wheel steering switch located on the Capt instrument panel underneath the Capt's clock.

[Flexman 30]

The Hydraulic System's is during pushback normally pressurized, Before the pushback driver start's with the pushback he install a lockout pin in the Nose Gear steering Lockout lever, This Lockout lever is pulled to block the Hydraulic pressure from Hyd A to the Steering actuator, Hyd B pressure is normally not used for steering. Alternate nose wheel steering is not automatic you need to switch it over with the Nose Wheel steering switch located on the Capt instrument panel underneath the Capt's clock.

Thanks. So is leaving HYD A pump switches off for "just in case"?

[ajacied551 1]

You can leave Hyd sys A OFF because it's not needed for pushback. But that is not my advice, Because than you have to Start Engine #1 after pushback, Do not switch OFF the Engine Driven Pump (EDP) if it;s not a emergency, you can damage the EDP solenoid. Most airline's are starting both engine's during pushback, Switching OFF the EDP is not a normal procedure in the checklist for engine start.So my advice is to switch ON the Hydraulic pumps during pushback and start all engine's and get going !!!!.

[Flexman 30]

You can leave Hyd sys A OFF because it's not needed for pushback. But that is not my advice, Because than you have to Start Engine #1 after pushback, Do not switch OFF the Engine Driven Pump (EDP) if it;s not a emergency, you can damage the EDP solenoid. Most airline's are starting both engine's during pushback, Switching OFF the EDP is not a normal procedure in the checklist for engine start.So my advice is to switch ON the Hydraulic pumps during pushback and start all engine's and get going !!!!.

...but. As a flight student I did many MANY jumpseat hours, and they always had both ELEC and EDP off on system A during pushback (pumps A off and pumps B on was in fact part of the before pushback flow). During pushback they'd start both engines up. After pushback, they would turn on both pumps on HYD A (engine1 being already on). Talking about Air Europa and the (now inexistant) Futura and i saw this both on -400s and -800s. Also, if my memory doesn't fail, I also saw this many years ago in Lan Chile's 737-200s. Also, and noticing you are an engineer, I have been told many times that fuel pumps don't need to be on for the APU, yet in both of these airlines I always saw a pump switched on for the APU. Are these pilot's "superstitions"?

[ajacied551 1]

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.