When taxiing with only two engines, i.e. to save fuel when you expect a long ride out to the runway, which two engines are better to use, the inboards or outboards? I saw this mentioned breifly in the manual, and became curious. Is this commonly done on 747s? I have seen it lots of times on smaller jets with tail mounted engines like MD-80s. However, its harder to notice this on a 747 from the passenger compartment, since the engines are so much farther away.Andrew

According to what the manual stated, it would be the inboards due to the fact that the outboards might not actually be over the taxiway and due to the risk of foreign objects in the engine...That is just how I read it though, I could be wrong...-PSelf BuiltLiquid CooledAMD 64 3400+2 Gigs Kingston HyperX DDR4006800GTRaid-0 Dual SATA Maxtor 120 Gig Hd'sDual Samsung 997 DF monitors

always use the inboards if possible (that's if your gross weight permits). ...otherwise the stray dogs that roam the tarmac will get very upset Capt.

>According to what the manual stated, it would be the inboards>due to the fact that the outboards might not actually be over>the taxiway and due to the risk of foreign objects in the>engine...>That is just how I read it though, I could be wrong...>-P>>>Self Built>Liquid Cooled>AMD 64 3400+>2 Gigs Kingston HyperX DDR400>6800GT>Raid-0 Dual SATA Maxtor 120 Gig Hd's>Dual Samsung 997 DF monitorsThat would make sense to me as well. On the other hand, using the outboards would give you more effective differential thrust if needed. I guess one could taylor this decision to the individual airport. Just curious how/if this is done much with these big birds. I can't help but imagine that on a flight from Newark to Tokyo, the crew is goign to want to save every drop of juice they can, especially considering the kind of endless taxi times you often get at Newark.Andrew

I was doing the KEWR-LLBG flight yesterday and I always watch flightview.com as I fly to try and see what the real plane is doing. They left the gate at 4:04 and got off the ground at like 5:30... They had almost a full hour and a half taxi. I have been on early morning flights leaving Newark where you leave the gate and start going in the opposite direction of the active because the line is so long that it gos the entire length of the active and wraps around the C terminals. I tihnk the worst was a flight to Pittsburgh where we were number 34 for takeoff... If I remember correctly and there was A LOT of information in that manual, they might have mentioned a one engine taxi as well. Am I making that up ;) -Paul SolkSelf BuiltLiquid CooledAMD 64 3400+2 Gigs Kingston HyperX DDR4006800GTRaid-0 Dual SATA Maxtor 120 Gig Hd'sDual Samsung 997 DF monitors

We only shut down engine #3 for taxi in after a 5 minute cool down time has elapsed. On taxi out for heavy gross weight takeoffs you would never taxi on 3 engines...the thing would never move and you would exceed your maximum N1 taxi RPM.

I have never experienced or even heard of a B744 taxiing on two engines regardless of taxi time. The extra thrust required of two engines to move the aircraft would negate any possible fuel saving.

well, if long wait times are expected (e.g. holding for takeoff), having 2 engines on idle is a lot more efficient than 4 on idle. a 744 will taxi with the 2 inboard engines only if there is a risk of foreign objects being sucked in, due to the outboard two overhanging the taxiway...

I know that lufthansa shuts down 2&3 (or only #3 if heavy) when taxiing in.

Here's a nasty taxi incident http://images.airliners.net/open.file?id=1...85&tbl=ACCIDENTI wonder if the info posted here is correct, though http://www.airdisaster.com/cgi-bin/view_de...rabian+AirlinesAre the brake hydraulics on the -300 powered by 2 & 3, or is that bs...? I couldn't find an authorised report on the incident.Jeff

>>Are the brake hydraulics on the -300 powered by 2 & 3, or is>that bs...? >>I couldn't find an authorised report on the incident.>>JeffAs far as I know they're driven by the number 4 engine on the classic although they can be run off the air driven pump so brake pressure can be provided by APU bleed air while on stand.

from the PMDG 747 manual... ;) hyd 1 : alternate brakeshyd 2 : alternate brakeshyd 4 : brakeseng 4 aux elec pump: brakes while towingLuca

Taxiing on two (or three) engines after landing is substantially different than taxiing out for departure. The difference between a max weight takeoff and a max weight landing is about 240,000 lbs. Unless the flight is from KORD to KJFK, it should be a four engine taxi. otherwise, anything behind you will be rolled up.Wes

Hi,this excerpt is from a US airline 747-400 AOM:"Using delayed engine start procedures and taxiing with one or more engines shut down is an approved procedure. A remarkable amount of fuel can be saved if flight crews use these procedures when appropriate. One minute of engine out taxi in the 747-400 is woth 3.7 gallons of fuel".

Hi,this excerpt is from a US airline 747-400 AOM:"Using delayed engine start procedures and taxiing with one or more engines shut down is an approved procedure. A remarkable amount of fuel can be saved if flight crews use these procedures when appropriate. One minute of engine out taxi in the 747-400 is woth 3.7 gallons of fuel".SORRY POSTED TWICE !