alt Hacker News"no fly zone" is one of those things that sounds obvious but if you actually think about it then it doesn't mean anything.
What mechanism gives the US the power to tell Russian planes where they can and cannot fly? The US cannot simply mark an area on a map. It would have to, at a minimum, deploy a series of surface-to-air missile sites to actually shoot down those planes that violated the map.
Presumably a combination of SAMs and fighter planes. The US couldn't put a no fly zone over Russia, but a no fly zone over Ukraine would be pretty straightforward (even just flying out of Germany). A no fly zone doesn't need to be perfect to work. If you shoot down a couple planes (or even have fighters in the area), you make every future flight by Russia a massive risk.