Surely it depends on whether you consider the question to be whether a certain Cruising Level may be allocated or whether vertical separation exists at that Level?
In UK airspace, as
vapourer rightly says, MATS Part 1 says in Section 1 Chapter 4:
6.5.4 Cruising levels at or above FL410 up to FL660 shall be selected according to the semicircular rule, therefore, Flight Levels available are:
• Eastbound FL410, FL450, FL490 etc.
• Westbound FL430, FL470, FL510 etc.
However, the vertical separation minima required are defined elsewhere, in Section 1 Chapter 3:
5.1.1 Vertical separation exists when the vertical distance between aircraft is never less than the prescribed minimum. The vertical separation minima are:
a) Between aircraft flying subsonic:
Up to FL290 apply 1000 feet;
Above FL290 apply 2000 feet, except that between FL290 and FL410 inclusive, 1000 feet may be applied between RVSM approved aircraft operating in airspace designated as being notified for the application of this separation standard.
b) Between aircraft flying supersonic and between aircraft flying supersonic and aircraft flying subsonic:
Up to FL450 2000 feet;
Above FL450 4000 feet.
In any case, as the original question relates to the allocation of a Cruising Level in Netherlands airspace, UK MATS Part 1 may not be an entirely relevant source.
JD
