What is the busiest domestic airport?
By domestic airport, I mean an airport where:
- all scheduled or charter flights are domestic, and
- the airport must not have any customs and immigration facilities for commercial flights (so it would not be possible to charter a plane to land there).
I don't know about customs and immigration for general aviation only.
- New York LaGuardia (LGA) or Washington-National (DCA) do not count; despite the absence of customs and immigration, they have international flights from Canada with customs preclearance;
- An airport in Germany or France lacking customs and immigration but having flights to only Schengen destinations does not count, because some of the Schengen destinations are in other countries.
By busiest, I mean largest number of passengers.
18 out of 20 busiest air routes in the world are domestic routes, but the world's busiest airports all serve many international flights. I would expect the busiest domestic-only airport in the world to be an airport in a large and populous country such as China, India, United States, Indonesia, Brazil, or Russia.