IFR Cruising Altitude Question

When flying IFR, your flight level should be even when flying westbound (HDG 180-359) and odd when flying eastbound (HDG 0-179). However, some flights, particularly those who’s destination is directly north or directly south of them, tend to switch between having a heading greater than or less than 180. When this happens, are you supposed to change your cruising altitude every time your heading switches from east to west?

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Great question! I would say no. You can just choose an even or odd altitude based on the main direction to your destination airport. You’re never going to have a perfectly north or south course. For example, if you’re flying from KSFO to KLAX, the FPL might go a little west for a bit, but as the bird flies, KLAX is east of KSFO, meaning you would fly an odd altitude.


The Newark to Singapore flight might be directly north or south at some point, but they stick to odd cruise altitudes as far as I know… I would just pick even or odd and stick to it instead of constantly changing it throughout the flight

Personally, no, I wouldn’t, but like @lucaviness, said, based on where you’re heading, you should pick between one of the two and stick with it. :)

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Well, especially if it’s a long-haul, you could be a little clever and plan step-climbs in that way - when you change direction you step to the appropriate altitude. You’d save a bunch of fuel as well!
But again, I don’t think it’s a requirement. Just a suggestion.

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When flying IFR it’s up to ATC in controlled airspace. Most real world IFR flights are almost entirely conducted in controlled airspace. Since IF doesn’t have specific LOAs or procedures, and most airspace is uncontrolled, it’s up to you. I suggest using the altitude that generally corresponds with your magnetic course.

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In Europe for example

Heading to the North is even
Heading to the South is odd

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