Aircraft fuel consumption

Hi everyone , I would like to ask whenever cruising at higher altitudes shouldn’t the fuel consumption be lower than cruising at lower altitudes? It seems like in IF is the other way around and dont ask me about my weight as this is a 3 hrs flight and my weight is just 34% so i am really light. I am flying the 777 btw and if flying at a lower altitudes does save fuel why dont airliners fly at a lower altitude ?

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It depends on your weight, thats why you should step climb

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Generally, the higher you get the lower your fuel consumption rate will be IF you have lost some of the weight you had before (aka step-climbing)

The science behind it is that as the air density lowers as you go up, in theory, the plane doesn’t need to use a lot of fuel to propel that less dense air, and thus, fuel consumption is reduced.

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It’s the other way around, flying higher requires less fuel as the air is thinner at high altitudes (less air = less drag). But it also requires more fuel to climb to that altitude, and more engine performance to climb through that thin air.

In the end, it’s all down to calculations and cost, and as @GBKarp says, that is why modern jets tend to “step climb”.

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I am pretty sure 34% is really light and dont even need a step climb lol this is a 3 hrs flight and i dont see 3 hrs flight stepclimb cuz there’s no point

Fuel consumption is lower at higher alts. Airliners don’t fly at lower altitudes because of a number of factors. Terrain can be one, and other aircraft flying at the same altitude can be another problem. Route distance is a third reason. If it’s a short hop, no need to climb to 36,000 feet.

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I am sure no 3 hrs flight would do a step climb and yes what you say is true IF physics might be wrong here but idk .

Some short flights might step climb. But, yes, you are right, usually they wouldn’t.

But at the same time, keep in mind, that these short flights aren’t achieving altitudes like FL400 or FL410 most of the time. They are probably max climbing to FL380-FL390. I see most of these at FL330-FL360 tbh

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Yeah, that’s what I was thinking

You are right, but it’s more explaining WHY step climbs exist. It is down to winds aloft, engine performance and cost index amongst other things. But cruising higher is more cost efficient, however getting there is the problem.

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Yeah, so although the cruise phase will burn less fuel, the climb up there will use more, so you have to balance altitude and time/thrust taken to get up there.

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Idk is this a physic error in IF or what but if you go test it out yourself you will notice flying at 30000 ft with a 772 uses up around 4600 ish kg of fuel per hour and that is with 34 percent load which is very light and as i climb to 39000 the fuel consumption goes up to 6000 kg per hour so i dont see how is that flying higher more efficient imo unless it’s an issue with the IF physics .

What were the winds like?

It’s a head wind

Jow strong? At both altitudes?

I won’t say stronger about the same around 21 knots?

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