Flight Level Cruise Heights
The International Semi Circle Flight Rule
When flying to my destination what height should I fly at?
All Aircraft Heading Easterly between 0-179 degrees will fly at Odd Flight Levels
All Aircraft Heading Westerly between 180-359 degrees will fly at Even Flight Levels
So if you were flying West from Cyprus to UK your flight level will be even flight level going to Cyprus would be an odd flight level.
Going to the Canary Islands from UK for some reason goes against the norm as going to Canary Islands are odd flight level and even coming back
Morning Shanwick Oceanic traffic up to 1000 hours UTC may fly at all flight levels when entering the UK airspace.
This has the following effect. If you were flying down a bi-directional airway Traffic passing you going the other way would pass you at a 1000 MPH crossing speed 1000ft above or below you. Your TCAS will have picked them up long before you can see them. To see a 747 going the other way with full con trail is a fantastic sight to see at Flight Level 370. Other rules apply for low level and VFR flights. it is important therefore that you maintain your cleared flight level at all times.So basically you work out which direction your destination is before adding the waypoints and apply the semicircular rule to the direct heading and decide whether it is going to be an odd or even flight level. Remember the higher you go the more fuel you will save. Aircraft going North out of Paris or London to cross the Atlantic are subjected to a maximum of Flight Level 280 South of Pole Hill VOR for ATC reasons. Some long haul aircraft will be to heavy to go above this in any case initially and will need to burn some fuel off.