Air travel is taxed not subsidized. As far as I know there are no subsidies to the airline industry, unless you get into very ideological arguments by claiming the US military is a form of subsidy to anything that depends on fossil fuels. Double checking Wikipedia confirms this. After a huge page listing all the taxes, there's one unsourced paragraph claiming that "some" governments subsidise air travel with a "who?" dispute filed against the claim:

https://en.wikipedia.org/wiki/Aviation_taxation_and_subsidie...

Road travel is usually profitable for the government as fuel taxes cover more than the costs of building and maintaining the roads. Drivers end up subsidizing rail in every country that I know of. It's possible EV cars will start to change this.

US passenger rail is nationalized. Amtrak is majority owned by the federal government, for example.