The search feature is pretty advanced! You can use special prefixes to refine your search. Suppose you want to search for a specific ICAO code. In that case, you can prefix it with icao:, for example icao:EPKT (note that you can search for it without prefix actually, but there cases where the system will find some other airports with the phrase in the name, for example). You can filter airports with has: prefix. There are currently three options: has:hardsurface, has:ils, has:lights. Try it for yourself, paste this into the search field: Germany has:lights has:hardsurface.