From a minimum of three high altitude jumps (it’s unclear just how many were actually required to get the three takes they needed) to the designing of never before used, completely functional, skydiving equipment, oh, and I forgot to mention the massive wind tunnel the production built at the beginning of all this just for rehearsal purposes, it’s absolutely insane that this was all done simply so this sequence could be done practically rather than via the use of digital effects.
It’s more than a little remarkable just how much work went into this one sequence that takes up barely two minutes of screen time.