Editing Flight level (section)

==Semicircular/hemispheric rule==
The ''semicircular rule'' (also known as the ''hemispheric rule'') applies, in slightly different version, to IFR flights in the UK inside controlled airspace and generally in the rest of the world.
The standard rule defines an East/West track split:

* Eastbound – Magnetic track 000 to 179° – odd thousands (FL 250, 270, etc.)
* Westbound – Magnetic track 180 to 359° – even thousands (FL 260, 280, etc.)

At FL 290 and above, if [[Reduced Vertical Separation Minima]] (RVSM) are not in use, 4,000&nbsp;ft intervals are used to separate same-direction aircraft (instead of 2,000&nbsp;ft intervals below FL 290), and only odd flight levels are assigned, independent of the direction of flight:
* Eastbound – Magnetic track 000 to 179° – odd flight levels (FL 290, 330, 370, etc.)
* Westbound – Magnetic track 180 to 359° – even flight levels (FL 310, 350, 390, etc.)
Conversely, RVSM equipped aircraft are able to continue separation in 2,000&nbsp;ft intervals as outlined in the semicircular rules. Both non-RVSM and RVSM equipped aircraft use a separation of 4,000&nbsp;ft above FL 410. 

Countries where the major airways are oriented north/south (e.g., New Zealand; Italy; Portugal) have semicircular rules that define a North/South rather than an East/West track split.

In Italy, France, Portugal and recently also in Spain (AIP ENR 1.7-3), for example, southbound traffic uses odd flight levels; in New Zealand, southbound traffic uses even flight levels.
In Europe commonly used [[International Civil Aviation Organization]] (ICAO) separation levels are as per the following table:

{| class="wikitable" border="1"
|+ Vertical separation of [[visual flight rules|VFR]] and [[instrument flight rules|IFR]] flights<ref>{{Cite web|date=November 2020|title=Application of Separation Minima|url=https://www.icao.int/EURNAT/EUR%20and%20NAT%20Documents/NAT%20Documents/NAT%20Documents/NAT%20Doc%20008%20-%20NAT%20ASM/NAT%20Doc%20008%20%20(EN)%20-%20Edition%2001,%20Amd%2010.pdf|url-status=dead|access-date=10 October 2021|website=International Civil Aviation Organization|archive-date=2 January 2022|archive-url=https://web.archive.org/web/20220102215351/https://www.icao.int/EURNAT/EUR%20and%20NAT%20Documents/NAT%20Documents/NAT%20Documents/NAT%20Doc%20008%20-%20NAT%20ASM/NAT%20Doc%20008%20%20(EN)%20-%20Edition%2001,%20Amd%2010.pdf}}</ref>
|-
! colspan="8" | Magnetic route figure of merit (FOM)
|-
! colspan="4" | 0° to 179° !! colspan="4" | 180° to 359°
|-
! colspan="2" | VFR !! colspan="2" | IFR !! colspan="2" | VFR !! colspan="2" | IFR
|-
! FL !! feet !! FL !! feet !! FL !! feet !! FL !! feet
|-
| {{n/a}} || {{n/a}} || 010 || 1,000 || {{n/a}} || {{n/a}} || 020 || 2,000
|-
| {{n/a}} || {{n/a}} || 030 || 3,000 || {{n/a}} || {{n/a}} || 040 || 4,000
|-
| 035 || 3,500 || 050 || 5,000 || 045 || 4,500 || 060 || 6,000
|-
| 055 || 5,500 || 070 || 7,000 || 065 || 6,500 || 080 || 8,000
|-
| 075 || 7,500 || 090 || 9,000 || 085 || 8,500 || 100 || 10,000
|-
| 095 || 9,500 || 110 || 11,000 || 105 || 10,500 || 120 || 12,000
|-
| 115 || 11,500 || 130 || 13,000 || 125 || 12,500 || 140 || 14,000
|-
| 135 || 13,500 || 150 || 15,000 || 145 || 14,500 || 160 || 16,000
|-
| 155 || 15,500 || 170 || 17,000 || 165 || 16,500 || 180 || 18,000
|-
| 175 || 17,500 || 190 || 19,000 || 185 || 18,500 || 200 || 20,000
|-
| 195 || 19,500 || 210 || 21,000 || {{n/a}} || {{n/a}} || 220 || 22,000
|-
| {{n/a}} || {{n/a}} || 230 || 23,000 || {{n/a}} || {{n/a}} || 240 || 24,000
|-
| {{n/a}} || {{n/a}} || 250 || 25,000 || {{n/a}} || {{n/a}} || 260 || 26,000
|-
| {{n/a}} || {{n/a}} || 270 || 27,000 || {{n/a}} || {{n/a}} || 280 || 28,000
|-
| {{n/a}} || {{n/a}} || 290 || 29,000 || {{n/a}} || {{n/a}} || 310 || 31,000
|-
| {{n/a}} || {{n/a}} || 330 || 33,000 || {{n/a}} || {{n/a}} || 350 || 35,000
|-
| {{n/a}} || {{n/a}} || 370 || 37,000 || {{n/a}} || {{n/a}} || 390 || 39,000
|-
| {{n/a}} || {{n/a}} || 410 || 41,000 || {{n/a}} || {{n/a}} || 430 || 43,000
|-
| {{n/a}} || {{n/a}} || 450 || 45,000 || {{n/a}} || {{n/a}} || 470 || 47,000
|-
| {{n/a}} || {{n/a}} || 490 || 49,000 || {{n/a}} || {{n/a}} || 510 || 51,000
|}
<!--does 51,000 ft represent an internationally recognised upper limit? -->