There are 2 airports close to the race site:
Brussels South Charlerloi (30min by car)
Flights with Ryanair from many countries: Denmark (from Copenhagen), France (from 13 cities), Italy (from 17 cities), Spain (from 13 cities), United Kingdom (from 3 cities), ….
Brussels Airport(1h by car)
Flights of many airlines.
Special mention: direct daily flight from Stockholm (Bromma) to Brussels (Zaventem)