A NFZ is not the answer...Putin is a sociopath and has no problem killing people. Increasing sanctions AND major corps leaving Russia sends a message Putin cannot ignore
You need to factor this in. Not everything is as simple as "send in the planes". SAMS would be more useful.
@Osinttechnical Ukrainian Air Force status per a senior US defense official-
80% intact 15 days after Russian invasion
Ukraine only flying 56 fighter jets 5-10 hours per day due to Russian SAM coverage.
Replying to @Osinttechnical I believe officials are right that more aircraft will not increase sorties if SAM cover is the problem. MiG-29's survivability couldn't be very high in that airspace if they pushed the issue.