Former air force major and engineer Hendrik Vercruyssen supplied the answer: "When the air force trains in Belgium it uses weapons and ammunition designed for exercises. When you see a plane on an exercise in Belgium, it is not carrying any real bombs. In Belgium there are no flights with real bombs. It's too dangerous. Belgium is too densely populated. Training using real bombs can occur in Germany, Norway and the US. Using real bombs would be more expensive."
"Training in Belgium occurs chiefly on the military estate of Houthalen-Helchteren. Belgian F-16's use large fake bombs, BDU33, weighing 12 kilos, and the smaller MK106 weighing 2.5 kilos. It's like a block of concrete hanging underneath the plane. There are no explosives in these bombs. A substance that creates smoke can be added."