At 2716.5 feet, Dubai's Burj Khalifa—which serves as a hotel, a conference center, and a residence—is the tallest building in the world. In the film, Ethan Hunt must access the hotel's server room from where it's most vulnerable: the outside of the building. This means scaling the exterior from the 123rd floor to the 130th floor. Initially, Bird planned to film the scene on a soundstage and fill it out with visual effects. But after talking to people in Dubai, he found out he had the irresistible chance to film the stunt in real life. "We could film Tom on the actual building," Bird says. "The more we started to think about that, the bigger our eyes got. Tom became really fixed on the idea of doing this amazing stunt and training for it."
While Bird planned out the shots and the stunt team scouted the Burj Khalifa for a place to shoot, Cruise got busy practicing for the climb. The production designer built a replica of the portion of the Burj for Cruise to practice on, and heated the set to simulate the actual conditions Cruise would face when doing the stunt for real (at times, the glass was as hot as 100 degrees Fahrenheit). The actor rehearsed the moves for months and trained with a rock climber to make sure his technique was accurate.
The base for the stunt was the Burj's 123rd floor, which was unfinished at the time of filming. "We could take our camera equipment and cranes and bash them around a bit and not hurt anything because the floors weren't finished," Bird says. The production crew had to remove 15 windows to gain access to the exterior of the building, rig the wiring for Cruise's safety harness, and extend the camera jibs outward.
While shooting, Cruise wore a harness attached to a cable system. A cable the size of piano wire was attached at various points along the length of the building; it was attached to Cruise's harness through a miniature pulley called a belly sheave, to control how tightly the actor was held against the building as he climbed. But climbing wasn't all Cruise had to do. For one shot, he also had to fall four stories; for another, he had to run across the face of the building and launch himself through an open window.
Bird says he wasn't nervous watching the star perform this crazy stunt—he was simply too nervous about getting the shot. "I didn't want to be the weak link that screwed up all this incredible infrastructure and preparation. So it wasn't until about 4 in the morning, when I was deep asleep, and suddenly my eyes snapped open and I went, ahh! What are we doing? When it was happening, I was just focused on not screwing up my part of it."
The crew filmed 13 shots over the course of four days on the outside of the Burj. "We planned it almost like a military invasion," Bird says. "I think the success of it is largely dependent on two things: getting cooperation from the people of Dubai, and then also having a star who's willing to go that high up and swing around on a very thin wire. It's a weird perfect storm of events, and I don't think it'll probably ever happen again."