Terrorism may also have happened at metro station Brusselsairport explosion: Terror attack? The Brussels Airport bombings today may represent a new wave and form of terrorist attack: Killing and maiming as many air travelers as possible in major airports with multiple bombs.
After 9/11/2001 major airports in the US and elsewhere had National Guard and some bomb detection installed for airport perimeters. Both those protections have been taken down and terrorists can now enter airports with bombs without much likelihood of detection.
While aviation security has made bombing or hijacking of airliners much more difficult, airport security is generally wide open. This needs to be tightened with perimeter bomb and weapons detection or else more airport bombings are likely to follow. Every new type of successful terrorist attack in history always generates copycat attacks until effective counter measures are put in place.