There was a simulation that made the rounds this last week that showed how aerosol droplets move around in the aircraft and it surprised a lot of people. One cough spreads mostly to a few rows ahead and behind the cougher but small amounts do move most of the length of the cabin.
The air is recirculated but is also refreshed. Not sure of the ratios.
This was featured in the last FlightAware newsletter - one airline is letting travelers buy up seats around their seat to enforce social distancing: https://flightaware.com/squawks/view/1/7_days/popular_new/78027/Passengers_Can_Now_Buy_Eight_Empty_Airline_Seats_For_Social_Distancing
Other airlines are requiring travelers to wear masks.
But the upshot is that with current aircraft and situation, air travel will be significantly more risky for travelers until they have recovered from covid and have some level of immunity. The amount of protection that provides is being studied and might not be much at all.
As the US heads into more states opening up from pressure from citizens who don’t understand the risks or math, and infections spike, air travel will likely get pretty risky. It’s going to be upended until we get a vaccine or enough in the population get immunity through having recovered.
And social distancing radically changes the economics of air travel. Until now, airlines maximized profits by cramming people into smaller and smaller spaces. You can’t do that in a covid environment.
Air travel will likely see a big decrease in airliners and an explosion in private jets and aircraft. Many will probably just drive.