It should be fairly easy for anyone to figure out that planes generally aren't used around-the-clock. For example, I routinely take a flight which arrives at 11pm, and I know that nothing is flying out of that airport again until the morning.

The difference being that setting up NS HA, then failing over to the secondary and rebooting in turns is a lot easier than doing the equivalent on a plane. So even considering the operational requirements are the same (no time to reboot but if you don't, people die), you still have a lot more flexibility.

The problem with an airplane is that by the time you find such an issue it becomes prohibitively expensive to fix if an "architecture" change is required. This is why workarounds are provided instead.