Why can't I use små here?
Lufthavn is singular here, and "små" can only be used to describe plural objects, for example:
Jeg har en lille kat => Jeg har små katte
Det lille hus ved kysten => De små huse ved kysten
(Christind Roselund) -en: Masculine or feminine words. -et: Used often with neuter words.
So why is it "det" and not "der" ?
You mean why is it "det" and not "den". That's what I want to know
Also want to know why Det and not Den?
Because "det" is neutral, I guess