Anytime the gun goes off inside the aircraft when it hasn't hit a body first, it will puncture the thin skin of the aircraft causing explosive decompression. Even if the bullet hits a body first, it still has a chance to go through and puncture the skin of the aircraft.
In the closing scenes, the aircraft is not a Boeing 747 as depicted in the rest of the film. It is actually a Boeing 737-400, wearing the markings of Alaskan Airlines instead of the correct Trans-Con scheme.
When the fuel tank gauge is shown, the letters "EGT" appear among the bars. Actually, the shot shows the engine exhaust gas temperature gauge instead of the fuel gauge. The two bars turning red would usually indicate an engine fire.
The terrorist shoots 23 successive shots at Martin while throwing the toxin out of the plane. The largest magazine capacity for a hand gun is 17 without some sort of extension, which is clearly not visible.
Jessica claims to understand the Czech terrorists, as her grandmother was Polish. However, the language hardly sounds Czech, and knowing Polish certainly doesn't help (very few words can be understood).