The (current) top thread in the comments section references the reduced vertical separation minima (RVSM): https://en.wikipedia.org/wiki/Reduced_vertical_separa

The (current) top thread in the comments section references the reduced vertical separation minima (RVSM): https://en.wikipedia.org/wiki/Reduced_vertical_separation_minima https://en.wikipedia.org/wiki/Reduced_vertical_separation_mi... It appears that there is a section of air between 29,000ft and 41,000ft, where flights are allowed to be closer than is normally allowed. Instead of 2,000ft apart, they are allowed to fly 1,000ft apart. In order to operate continually in this airspace, a plane must be "RVSM approved". Otherwise they have to either request special permission or make a continuous climb through said airspace while complying with their usual 2,000ft requirements. The article mentions that the A380 and Challenger 604 were 1,000ft apart. So, I would assume they were both RVSM approved. This event could call the RVSM into question.