[Oil Object Insp]

I’m uncertain how AF-1 is set up, however most airplanes, even small ones the air is not circulated, but rather there is a over pressure and dump valve that allows a constant flow of air out. This doesn’t stop people from being effected by the air on the way out.

[ought-six]

From various websites: "The most efficient HEPA filters will capture 99.97% of particles between 0.1 and 0.3 μm and 100% of the other particles. SARS-CoV-2 (Covid-19) is an enveloped virus ≈0.1 μm in diameter." So, HEPA filters (modern aircraft have these) may or may not filter out a Covid-19 particle.