Continuity mistake: During the stop-over at Limassol a maintenance guy places a fully-zipped clothes bag full of, as we will see later see, weapons in a cabin wardrobe. Before the plane takes off a stewardess happens to see the bag, which is now zipped down half with a gun sticking out. The wardrobe is a different one too, since a large sign with seat directions, which was placed next to the wardrobe, isn't there anymore.
Revealing mistake: When Jack breaks into the Albert Dock Road building where the hijackers have their hideout, he enters through a wire-mesh-reinforced roof window. From below you see that he hits it once, causing a huge shower of big glass pieces (as if there were no wire mesh), and then the whole, almost intact pane comes down as if the mesh hadn't been connected to the frame.