# Why do airliners over south-west Europe cruise at flight levels with inversed numbers?

Over North America and Europe, usually when airliners go east (heading 0-179) they cruise at a flight level with an odd number (e.g. FL370) and when going west (180-359) they cruise at an even number (e.g. FL380), right?

When looking on flightradar24, all planes follow this pattern except for planes flying over south-west Europe (Iberian peninsula, Cote d'Azur, Mallorca and so, as well as Morocco): there, planes flying to the east cruise at even numbers and to the west at odd numbers. Why do planes flying over or near the Iberian peninsula have the flight levels inversed?

• My guess: since the majority of traffic is North/South, they have even for northbound and odd for southbound. Commented Dec 8, 2022 at 11:24
• @Sanchises Where they fly from/to doesn't matter, planes flying e.g. at heading 90 (east) cruise at an even number near the Iberian peninsula, when elsewhere above land the norm is to fly at an odd number east. Commented Dec 8, 2022 at 11:36
• ATC in Florida turns the hemispherical rule 90 degrees (for all traffic) due to the dominance of north-south flows. Maybe Spain does the same? Commented Dec 9, 2022 at 17:43
• @StephenS Yes, maybe. I'm also suspecting Spain to have something to do with the inversion. Commented Dec 10, 2022 at 6:59

The above persons guessed correctly. Since a majority of flights in the area fly in north / south directions, rather than east / west, France, Spain, Italy and Switzerland generally apply the NorthEVEN and SouthODD rule. In Germany, some airways also follow this rule on their course between the Swiss and Danish airspace. This is easily seen in enroute IFR charts.

You can also check it, for instance, in the Spanish AIP, ENR 1.7.3, here:

Spanish AIP, ENR 1.7.3 , page 3.

In the French AIP section ENR 1.3.5, you can see how they interestingly use the east / west rule for IFR flights below FL200, and the north / south rule for IFR flights at or above FL200.)

French AIP ENR 1.3.5.

• Welcome to aviation.stackexchange.com, @esther! Commented Jul 11, 2023 at 12:43