Factual error: The payphone McClane uses in Dulles airport has the "Pacific Bell" logo. Pacific Bell is a West Coast phone company.

Factual error: Prior to the 747 take off, a bad guy is sucked by one of the engines and all we see is blood being spit from its exhaust. Turbofans are very sensitive and may collapse by sucking a heavy bird (like a vulture), but this one stayed undamaged after sucking a 200 lb man.

Continuity: The scene where Richard Thornburg is in the aeroplane bathroom giving his live report, in a number of the shots he is holding the phone upside down.

Continuity: Bruce Willis is emerging from an underground air-vent when the plane with General Esperanza is landing. Initially the plane is coming on a direct course for him and he struggles to get out. In fact the front wheel is on course with and knocks the vent cover. But in the very next scene, the tire marks clearly show the front wheel passed to the right of the vent and so completely missed it.

Factual error: The terrorists some how raise the elevation of the airport in relation to the ILS (instrument landing system). This causes one of the jets to crash. The ILS glide slope is broadcast from a fixed antenna beside the runway, 1000 feet from the approach end. The glide slope is fixed at (usually) 3 degrees. Even if someone changed the slope (ie, degrees of slant), it would still terminate on the runway at the touchdown zone. Besides, the pilots have charts that give all pertinent information about the ILS and also have altimeters, radar altimeters, ground proximity warning systems (GPWS), and brains (duh). They would not have descended into the ground even if the terrorists had tampered with the ILS.

Factual error: When Holly's plane finally lands, the cockpit shot shows the pilot with his hands on four engine throttles. But Holly's plane is an L-1011 TriStar, which only has three engines.

Factual error: When McClane (Bruce Willis) is brought into Capt. Lorenzo's (Dennis Franz) office at Dulles Airport for the first time, Lorenzo mentions that McClane was in violation of several District of Columbia laws. Dulles Airport is in Virginia, not DC, therefore any DC laws would not apply to Dulles. (Although VA may very well have similar laws about airport misconduct.)

Revealing: In the skywalk scene, when McClane pushes the paint stand on the terrorist, you can clearly see that they use a dummy when the paint stand falls on the terrorist.

Revealing: At the end of the film when John and Holly get driven away on the back of what resembles a golf cart, the long shot of them clearly shows two dummies that nearly fall off when the cart sets off.