Originally Posted by IO540
No dispute about needing to land at a Customs airport if one is landing non-Schengen etc etc.
The Q is why one needs to clear Customs when the actual activity is just a refuel, when everybody can remain airside.
IO540 - your question seems to imply that airside is some sort of international no-man's-land, rather than part of the country itself. Whilst states have the option of treating it as such, it need not necessarily be so and probably isn't ever treated as such. In the UK it plainly isn't so - you can clear customs from many airfields that have no meaningful border between airside and landside. Although not as obvious, it's the same at a number of foreign airfields - for example La Baule, Courchevel, Saanen and Lausanne. Conversely, you can be airside at an international airport with a clear distinction between airside and landside - for example Paris CGD and Orly - and you still need to meet the transit visa requirements even if you're not even getting off the aircraft.