February 12, 20179 yr 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 Bryan Richards "People depend so much on automation that they forget how to get the automation to work." B.W.
February 12, 20179 yr 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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