Flight Level information?

Pro Member First Officer
William A. Jones (waj2306) First Officer

For the longest time, I have used the flight level shown on the Create Flight screen, that uses 3000, 4000, 5000, ect. I know this is not acurate, and would like to find some help on setting the Flight Level at a more realistic altitude.

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Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

Do you mean what flight level you should select or when you should start referring to altitude as flight level?

Flight Levels are used after the Transition Altitude - the point at which every aircraft will change their altimeter subscale setting to 1013mb or 29.92hp as to measure height above a fixed datum point rather than a local pressure setting.

The transition altitude varies from country to country. In parts of Europe, it ranges from 3000ft to 6000ft or more. In America, the transition altitude is 18000ft.

If you want to know how to select a flight level, I'll give you more info.

Pro Member First Officer
William A. Jones (waj2306) First Officer

Let'r roll! You are just what I need on this subject! Thanks

Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

I wrote this for someone in 2006. This have changed slightly in controlled airspace with the advent of RVSM (Reduced Vertical Separation Minimum) which allows airliners to fly with a 1000ft vertical separation as opposed to the previous 2000ft. As far as I'm aware, RVSM is only used in CAS (controlled airspace) whereas the below is for OCAS (outside controlled airspace).

99jolegg wrote:

Jamie4590 wrote:

What altitude is the start of IFR where regardless of conditions you have to use instruments and keep ATC informed of your plans?

Yes, Class A airspace is strictly IFR only which starts at 18,000ft and ends at FL600.

Below FL245 - Quadrantal Rule:

The Quadrantal Rules stipulates that when flying IFR above the transition altitude (outside of controlled airspace) the PIC must select a Flight Level for cruising based on the quadrantal rule.

Excuse my crude demonstration courtesy of MS Paint:

A = An odd flight level between 000 - 089 degrees
B = An odd flight level + 500ft between 090 - 179 degrees
C = Even flight level between 180 - 269 degrees
D = Even flight level + 500ft between 270 - 359 degrees

For example, if you are flying below FL245 and above FL30 in a direction of 156 degrees, then you must fly at an Odd flight level (FL130) + 500ft i.e. fly at an altitude of FL135 or FL155 etc.

Above FL245 - Semi-Circular Rule:

This is slightly more simple. Above FL245, in an Easterly direction, i.e. flying in a direction of 000 to 179 (A and B in the diagram), then you fly at an odd Flight Level, i.e. FL250, FL270, FL290, FL310, FL330, FL350, FL370, FL390 and FL410. After that, you fly at 4000ft above.

In a Westerly direction, i.e. between 180 and 359 degrees (C and D in the diagram), then you fly at even Flight Levels, i.e. FL260, FL280, FL300, FL320, FL340, FL360, FL380, FL400, FL430 (yes, its the exception for some reason) and then 4000ft higher than that if you want to fly higher.

Remember, all of the above is for uncontrolled airspace. If you are in controlled airspace, the Flight Level for cruise is dictated by your flight plan.

Hope that helps - don't hesitate in asking if you have any other questions 😉

Pro Member First Officer
William A. Jones (waj2306) First Officer

This is perfect! Without a doubt, the best explanation I could hope for. I am printing this out and will be using it for all future flights.

Thank you so much!


Pro Member Chief Captain
Jonathan (99jolegg) Chief Captain

No worries.

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