The North Atlantic Treaty Organisation is known as NATO. Twelve countries, including the USA, Canada, the United Kingdom, and France, joined the military alliance in 1949. In the event that one of its member states is attacked by military forces, the other member states must band together to defend that country. Ukraine's main purpose, according to Russia, is to avoid joining the Internet, which would jeopardise regional security.
Gelenskky is adamant about declaring a no-fly zone. When an area is declared a No Fly Zone, warplanes, drones, and even passenger planes should avoid flying above it. If a no-fly zone is imposed during the non-combat period, aircraft attempting to fly through it may be shot down. iraq was proclaimed a no-fly zone by US and NATO forces in 1991. It is forbidden for the UN to fly over libya in 2011.
However, if ukraine announces a no-fly zone, the US and NATO will be forced to commit troops to protect Ukrainian airspace. However, doing so would open the door to a direct conflict with Russia. That is why NATO has refused to declare a no-fly zone over ukraine and some nations.