The HALO skydiving sequence (distance of 7 km / 25000 feet, traveling speed of 265 - 320 km/h) was the last sequence filmed during production, but it was the first stunt designed and required a full year of planning out. The crew had only a limited time window of three minutes a day during sunset to film a jump. Because of strict air aviation regulations in France, it could only be shot in the Emirates. It took Tom Cruise, Henry Cavill, the skydiving camera operator Craig O'Brien (who was instructed to keep a distance of three feet from Cruise while filming) and others involved a total of 106 jumps to get three possible takes. However, to rehearse the sequence, the crew built a custom oxygen helmet with RAF assistance that can be lit up to see a face, and then also built one of the world's largest wind tunnels for practice. The practice doesn't end there - Cruise and the other persons involved did five skydives a day with one in the morning, three in the afternoon, and one at dusk. Some of the other cast members turned up to visit, with Simon Pegg saying that he and his co-stars thought multiple times that Cruise was seriously about to die: "It is a daily stress going to work with him, because you don't know if you are going to see him tomorrow."
Tom Cruise trained for an entire year to perform the HALO (High Altitude Low Opening) stunt in this film.
In August 2017, Tom Cruise suffered an injury while filming a stunt jumping from one building to another. He was able to grab onto the other building thanks to a harness strapped onto him and to his history of performing his own stunts for action films. However, his ankle fractured upon the impact of the jump. Cruise then got up and attempted to run it off, as this was in the middle of a chase scene, before he and the crew decided to stop filming. Shooting was delayed for eight weeks following the injury. The footage of the stunt used in the film and its trailers just so happens to be the actual injury. To this day, Cruise still refers to this stunt as the easiest of all he's had to do for this film.
Rescuing another person in free fall while skydiving is very difficult. Allan Hewitt says that "it takes Accelerated Free Fall instructors over 1,000 jumps to get it right and something like 70% of the people who try to qualify at the instructor level fail. Tom had just 100 jumps to perfect this."
While Tom Cruise (Ethan Hunt) is famously known for performing his own stunts throughout the films, he ups the ante in this installment by performing four elaborate set pieces (mostly without green screens or stunt doubles): a HALO jump, an unusually dangerous variety of High-Altitude Low Opening parachute jump; a helmet-free motorcycle chase through Paris, including a portion in which Hunt rides against traffic in the circle around the Arc de Triomphe; an extended foot chase across London rooftops, in which Cruise broke his ankle while jumping between two rooftops; and a helicopter chase in which Cruise does most of the piloting.