Hello,Just wondering if there are any restrictions to the max and min altitudes allowed for Upper and Lower airways.Mike

I may not be right, and also speak for the US, but I think that the division is in the FL180, and there's also the rules of the exact altitud depending the heading you are flying

AFAIK Lower/upper airway boundaries are 18,000ft USA & 24,5000 Uk & Europe, and don't forget that transition altitude in UK (Europe?) varies from airport to airport, unlike the USA.I *know* if I get it wrong someone *will* correct me :-)

you're right Vulcantransition altitude depends in Europe on airport/countryin most countries, 24500 is the boundarie,but also 19500ft is often used