Originally Posted by
Modo
How do they deal with passengers who do not have a Schengen visa when this happens?
I'm not sure what the Spanish policy is, but the general Schengen guidelines give border authorities certain leeway when passengers end up in Schengen unexpectedly and "against their will". In such circumstances, a short term visa can be issued at the border. (I assume the same will apply to ETIAS once implented.)