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Higher/lower Altitudes And Fuel Burn  
User currently offlinePHX787 From Japan, joined Mar 2012, 8384 posts, RR: 20
Posted (3 years 11 months 1 week 3 hours ago) and read 4627 times:

Simple question: when it comes to fuel efficiency, is it preferred to be at a higher altitude (FL37+) or a lower altitude (FL32-) to have better fuel efficiency, or in between?

Does anybody have any stats for ULH planes (747, 777, A340, A380) and their fuel burn in comparison to altitude?

Thanks, Z

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3 replies: All unread, jump to last
User currently offlineAF1624 From France, joined Jul 2006, 696 posts, RR: 0
Reply 1, posted (3 years 11 months 1 week 2 hours ago) and read 4610 times:

It strictly depends on gross weight, CG, temperature and winds.

The FMC (on aircraft equipped with it) will work out an optimum altitude depending on these factors + some others.

As a rule of thumb, higher altitude = thinner air + lower temperature = lower fuel burn


If the aircraft is too heavy, higher altitude = thinner air = higher angle of attack to keep level flight = higher fuel burn

AND of course winds play a big part in it.

That's pretty much how it works.

Usually, an airliner will do step climbs. i.e. start cruising at FL350, and then as fuel levels diminish weight decreases so 370, then 390, then 410.

User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2268 posts, RR: 6
Reply 2, posted (3 years 11 months 6 days 20 hours ago) and read 4506 times:

Our dispatchers also plot say 4 routes and altitudes and choose route/altitude based on the best for time and or fuel burn depending on what's most important for that flight.

User currently offlineMir From United States of America, joined Jan 2004, 22865 posts, RR: 53
Reply 3, posted (3 years 11 months 6 days 10 hours ago) and read 4345 times:

It is, in general, better to be higher. However, if you're too heavy for a certain altitude, then you'll burn more fuel than you would if you stayed lower down until you became light enough to climb up. Aircraft will have an optimum altitude for a particular weight, and and significant deviation from that will result in higher fuel burn. The optimum altitude will increase over the course of the flight as the aircraft burns off fuel and becomes lighter.


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