There's a new MIT study out highlighting the struggles of small- and medium-sized airports, which over the past five years have seen 18.2 and 26.2 percent declines, respectively, in domestic flights. This means that people served by these airports have less options, and also that the costs of their flights have increased faster than those at larger regional airports.
NPR has more on the specifics.
First, I just want to point out that this means service is objectively worse for travelers over this time period, even with continued federal and state investment in airport infrastructure. Unlike what we see with Amtrak, however, I have yet to hear any politicians threatening to pull the plug on the $4 billion in federal (and who knows how much state) spending on airport construction, or the billions we spend on security and traffic control. Are they okay with continuing to prop up an airline industry intent on withdrawing service from much of the country?
Perhaps a better analog of Amtrak's service--the unprofitable long distance routes, at least--is the US DOT's Essential Air Service. It saw the smallest decline in flights of all airport types, five percent. The EAS was created in 1978, coincident with the deregulation of private airlines, and was "put into place to guarantee that small communities that were served by certificated air carriers before deregulation maintain a minimal level of scheduled air service."
This service costs over $200 million a year, with most of the ~150 affected airports only making a few 19-seat flights a day; you can bet it serves far, far fewer passengers than Amtrak's 5 million annual long-distance passengers, or its 15 million state-supported route passengers. (Amtrak requested $373 million in operating support this year, a number that has been declining rapidly in recent years as ridership has soared.)
I genuinely have nothing against the airline industry, and actually think their private, deregulated system is pretty effective. As a whole, the airline industry also serves many more passengers every year. I don't even really mind the EAS much, although there are some cases where it's clearly being abused. The point is that just as with our system of roads and highways, no travel mode comes without some amount of subsidy (nor should it--mobility is an invaluable public good). Despite this, only rail and transit are portrayed negatively for their dependence on public support.
This double standard is ridiculous, but especially so for the following reason. We spend hundreds of billions of dollars on roads every year and tens of billions on airports and security, and does anyone honestly think either driving or flying has gotten any better? Rail, transit, and bikes on the other hand, the most scorned forms of transportation in this country, and worst funded, are only becoming safer, more convenient, and more popular. I don't even know who the joke is on.