If you get an elytra from around 30k feet(avg commercial airline height I think) and 30k feet = 9,144 meters. One block in minecraft is 1 meter. An elytra give about 10k blocks(10k meters) and 7min of flight time. The elytra will make it to the ground with a few more blocks to fly. But let's just say it was a private jet at around 40k feet which is about 12k meters. You wouldn't make it to the ground with just one unenchanted elytra. Yes I did my research.