It depends where you're flying, or the airline base. The US is one of very few countries who declined to sign a treaty regarding the usage of "champagne" on labels for bubbly produced here. The "champagne" name is a domain. Most (maybe all) Eu nations have their own names: Sekt (CZ), Cava (SP), Espumante, etc. This is why we have "Cook's Champagne" (cheap, but good enough for casual quaffing)...