FL 420 invalid?

[damien]

I am not a real world pilot so please forgive me. Flew this westbound flight http://peaware.pilotedge.net/flight.cfm?id=38692 and filed for FL420. Controller said something to the effect of FL420 being invalid and gave me 430 instead. Can anyone help please explain why?

[Kevin_atc]

RVSM (Reduced vertical separation minimum) ends at FL410. RVSM allows aircraft to be separated by 1000ft vertically. With that said, Any aircraft above FL410 must be separated by at least 2000ft vertically so with aircraft cruising at FL410, FL420 doesn't work because that's only 1000ft above. So, above FL410 the typical even for west and odd for east altitudes don't apply.

FL390: Odd
FL400: Even
FL410: Odd
FL420: N/A
FL430: Even
FL440: N/A
FL450: Odd
FL460: N/A
FL470: Even
FL480: N/A
FL490: Odd
etc...

[Andrew Doubleday]

Technically I suppose you "could" cruise at FL420 in consideration to the fact that there isn't anyone else operating at FL410 on a converging flight path that would "tie" with you at some point along route of flight... It's good practice for ATC to inform about the mistake and probably not allow it in best interest of safety and basically CYA should anyone else decide they want to climb up to 410 though. The controller would need to ensure either appropriate vertical separation would exist prior to a conflicting aircraft reaching a 5nm lateral radius around you (en-route separation minima) if it were only 1000 feet separation between you and someone operating within RVSM airspace that was RVSM capable. I'm getting a bit technical, I know, but that would be why the controller wouldn't want to just reasonably allow it taking other pilots into consideration.

[damien]

got it. thanks!