Then, the first positive result that you get should mean that the whole plane is at risk, after all we are talking of people that have been jammed together on the plane for some 8 hours (on the same recirculating air) and then kept (possibly also jammed together) for another 5-6 hours at the airport to wait for the results, that is - from what I can understand of the way the virus is transmitted - the perfect environment to diffuse the virus.
The only meaningful way I can imagine (not doable in practice) is having travelers lodged at a departure airport hotel, and be tested before taking the flight.
This (the recirculation part) is likely less tragic than it seems.
Air recilculated on the airplane goes through a HEPA filter and the whole air is exchanged every 3 minutes. HEPA filters are able to catch the virus as far as I know.
The only meaningful way I can imagine (not doable in practice) is having travelers lodged at a departure airport hotel, and be tested before taking the flight.