From the CEOs of Southwest and American, testifying during some Congressional hearing:
“I think the case is very strong that masks don’t add much, if anything, in the air cabin environment. It is very safe and very high quality compared to any other indoor setting. High-grade HEPA air filters on planes capture virtually all airborne contamination and air quality is helped by how frequently cabin air is exchanged with fresh air from outside the cabin.”
So much for masking policies on airliners.