Can some enlightened ATC boffin answer my question. Just curious yesterday evening flying over the Netherlands to Ireland at FL400 I asked the controller for the next level up - he said you can have FL410 or 420. Well without sounding like an amateur I have never heard of this - being cleared to that level. 410 and 430 etc always get the limelight i guess there isnt anything wrong with 420 but I am puzzled i didnt think it was a level?
