You Don’t Always Need to Cruise at High Altitudes

I feel like a lot of the time I see people cruising at unnecessarily high altitudes like some even being a few thousand feet above flight level 400. Remember, planes in real life don’t always fly at the their ceiling. Many flights from the North East and New England to Charlotte and Florida sly over my house and because of the constant 100 knot wind blowing due north right above my house some of these planes fly over at between 24-28 thousand feet. These flights can easily reach cruising altitude because they’re 2-3 hours in length, but they don’t. On the other hand I sometimes see 737s and other smaller airliners fly over my house at 38,000 feet or above. I think it’s kind of interesting how variable cruising altitudes are and it’s all based on winds, so remember, high doesn’t mean faster, but less of a headwind does. :)
(If this doesn’t belong in Real World Aviation let me know)

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Normal long haul cruises are near the aircraft’s ceiling. It’s also normal for aircraft to cruise at FL390.

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This is the amount of aircraft cruising above FL400 over the US right now.

It all depends on many factors. Today, I flew a CCX flight at FL460. Ceiling is FL510. Winds were slower, and I avoided all other traffic I may have come across.

Good points, though.

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If someone knows how this works, I’d like to know.

Years ago, I flew DFW-LAX on American Airlines’ MD-80. However, we had a scheduled fuel stop in Albuquerque. From what I can remember, there was some issue that required us to fly at a much lower altitude… it might’ve been something to do with cabin pressure.

Because we were flying lower than normal, that made us stop in ABQ for a refuel. So does flying at higher altitudes conserve fuel? Or is it dependent on the jetstreams?

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The air is thinner at high altitudes so engines work better and burn less fuel but I don’t know why the low altitude would’ve been such a fuel waster on a short flight like that

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We cruised at FL240 on my STL-DFW MD-80 flight. I believe you experienced the same thing.

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As @NoahM already wrote the air density is much lower at higher altitudes, which reduces the fuel burn.
Also winds can be stronger.

The air density is the main factor from my knowledge though and can influence the fuel flow quite a bit.

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I always tend to cruise between FL380 - 410, but sometimes certain airlines like to cruise higher because it saves fuel.

Also, some business/private jets cruise as high as FL450!


This post was taken at FL450.

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I saw a CCX flying at FL510 once.

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It highly depends. Weight is the main thing. Cruising higher is slower up to a certain point. Also if you are heavy enough, 390 can be less efficient than 370 because high AoA.

I’ve never heard 510 before, that’s impressive 😂

For engineering reasons I won’t get into, an aircraft should always fly at its design lift/drag ratio (L/D). That’s why altitude typically varies between FL300 and FL410 as fuel is burned. Since L goes down you need to reduce D to stay at the optimal ratio. Of course on shorter flights it isn’t reasonable to climb to those altitudes though.

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That’s legit my computer background

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I will try and take a picture for you to show you the fuel burn at 10k, 20k, 30k, and 40k.

While commercial airlines in the ideal world would love to save fuel every leg, it hard to do so. Weather, temps at altitude, loads and flow of traffic into the airports are huge factors. However, dispatchers do their best to get the plane as high as possible to be as efficient as possible. Then it up to the pilots.

This is completely different in the corporate world. We try and save money with alt every chance we get. Even on a 80nm flight we will get to get to 32-35. ATC at times won’t allow it , but sometimes we get to do it. We end up saving about 200 bucks on short trips and factor in 30 planes doing this and you will see how much money is saved This is also done more in the corporate world because pilots get bonuses on fuel savings in two forms. One in cost of fuel per gallon in picking the right place and the other for fuel burn.

https://www.aopa.org/news-and-media/all-news/2002/january/flight-training-magazine/behind-the-power-curve

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.fzt.haw-hamburg.de/pers/Scholz/arbeiten/TextBurzlaff.pdf&ved=2ahUKEwi_o7yUm-blAhVJbKwKHU2AA84QFjABegQIDhAK&usg=AOvVaw2wND5tFODC2YKSDmcq7vDl

This is long but addresses it. You will have to download it

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So I was on two WN flights not too terribly long ago. Both 737-700WL-first was BOS-MDW about 2.15 tops, cruise was FL400 I was shocked. The second one was BWI-BOS-all of 80 minutes if it was that. Cruise level: FL390 again, shocked. DCA-BOS (slightly further than BWI and along the same exact route except for the SID) routes are often capped at FL270 (A320/E190/E170 etc.)

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@Bravo59 This is a FL510 moonshot from one of my other posts. (You might want to put your brightness up)

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Forgot to post these pics.

Fuel burn at 360 at cruise power 1508 burn/ hr

Fuel burn at 450 at cruise power 994 burn/hr

The difference in fuel burn will allow you to fly about an hour or more extra with zero wind. That’s a pretty big difference in making a fuel stop or non stop.

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I think this general rule of thumb does not necessarily apply to every aircraft. The 777-300ER for example, is considered “underwinged”, which means its wings cannot generate enough lift at higher altitudes. I know it seems like a bold claim, but if you check FlightAware the 777-300ER usually ends its step climb at around FL350-380, you never really see it at FL400 or above. So it’s really a matter of what fits the aircraft best.

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Not sure how accurate fuel burn is in IF, but I’ve actually done a fuel burn table in IF at M.84 and the conlusion was indeed climbing about FL380 is not efficient.

lowest cruse attitude i flown was 23,000ft by dash 8 Q400 and highest was on B789 long haul was 40,000ft