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A340-4

Impossible to Taxi with ENG 3-4 Off

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Hello;

Is it just me, or is it impossible to taxi her with N3-4 been off? 

Thank you. 

 

Best Regards,

 

Vasily B.

 

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Not to heavy, as I have tried to taxi after completing a 8 hr flight with her. 

What i mean is that you cant turn her. 

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I turn off 2 and 3, as those are closer to the fuselage where the ground service vehicles will be wanting to get to. Turning off 1 and 2 or 3 and 4 seems less helpful.

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I generally turn off engines 1 and 4. That way it is easier

 

Bad idea if you want to turn or stop though (think about which hydraulic systems power the brakes and steering...).

 

As Wes says, if you're going to do engine-out taxi on the 747 then the normal thing to do is to shut down 3, or 2 and 3.

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Lads,

Im not asking about SOP or what some companies do to save money. All I am saying is that if you turn off N3 and N4. You cant turn her. Is that a bug? Or not? 

 

Thank you. 

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I cant turn left. It will turn right on its own with only 3% GW.

 

It isn't a bug. Hyd system 4 powers the nosewheel and body gear steering. So it's not surprising you can't turn left. It will want to turn right because of the thrust asymmetry you have.

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It isn't a bug. Hyd system 4 powers the nosewheel and body gear steering. So it's not surprising you can't turn left. It will want to turn right because of the thrust asymmetry you have.

Wouldn't the demand pumps take over from the engine pumps tho so the NW steering would still work?

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Wouldn't the demand pumps take over from the engine pumps tho so the NW steering would still work?

 

Yes

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Wouldn't the demand pumps take over from the engine pumps tho so the NW steering would still work?

Yes, but at idle thrust on only two engines and with three packs on there might not be enough duct pressure to fully power the hyd system.

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Yes, but at idle thrust on only two engines and with three packs on there might not be enough duct pressure to fully power the hyd system.

Ah I see. So a possible workaround to get the steering back would be to switch the demand pump 4 to AUX, or would that not provide enough pressure to steer?

 

 

Edit: Oh never mind, I just looked at the hydraulic diagram. Nose gear steering is on system 1, so unless you've got the AUX pump installed also on system 1, shutting down engines 1 and 4 are generally no no

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It isn't a bug. Hyd system 4 powers the nosewheel and body gear steering. So it's not surprising you can't turn left. It will want to turn right because of the thrust asymmetry you have.

Correction, nose and body gear steering is from system 1, not 4, my mistake. (I should never rely on memory for these things when posting here.) I just tried taxiing on eng 1 and 2 only and while turning is less easy to the left it is possilbe unless asymmetric thrust is high. Also the pneumatic demand pumps are producing 3000 psi so there is sufficient pressure in systems 3 and 4.

 

That being said I don't think two engine taxi is a common procedure in the 747 (it is in the A380). If you did need to shut down two engines it would make more sense to have one engine on each side, ideally 2 and 3, and use demand pumps 1 and 4 to power brakes and steering.

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