Liege Airport

Police checks

Which passengers are checked ? 

Passengers travelling to or from destinations outside the Schengen zone will be subject to police control.
You will therefore have to undergo these controls if you are leaving to or coming back from AGADIR, ANTALYA, BODRUM, DJERBA, HURGHADA, IZMIR, MONASTIR, PRISTINA, TEL-AVIV, TETOUAN and TIRANA.

Where do these checks take place?

At Liege Airport, police checks for departing passengers are carried out on the first floor, after the duty-free shop and before entering the boarding lounge. If you need to be checked, don't wait for the last minute before coming to the check-in counter!
When you return, you will be checked when you enter the non Schengen arrivals room

YOU MUST ALWAYS HAVE YOUR IDENTITY CARD AND/OR PASSPORT AND/OR VISA, DEPENDING ON YOUR DESTINATION, ABOUT YOUR PERSON.

http://www.diplobel.fgov.be/en/travel/traveldocs.asp