20 Things You Somehow Missed In Die Hard
19. Falling Down The Air Shaft
Following a close encounter with Gruber's chief lieutenant, Karl (Alexander Godunov) and his goons on the rooftop of Nakatomi Plaza, John McClane crawls back into the building through a ventilation shaft (often mistaken for a lift shaft).
As he is crawling down the shaft, McClane slips and breaks his fall by catching the lip of a lower air duct, thus saving himself from a harrowing fall all the way down the inside of the building.
The thing is that this was a mistake. The stuntman doubling for Bruce Willis had unfortunately slipped in the shaft and missed the first air duct, which he was meant to climb into, catching the second instead.
Director, John McTiernan and editors, Frank J. Urisote and John F. Link managed to save the scene through some sly editing, but this simple slip which could happen to anyone helps to demonstrate to the audience that they are not following the exploits of a Schwarzenegger or a Stallone - they are following an average man trying to save the woman he loves.