There were over 1100 commercial air flights in the skies at the time of the attacks. All of those pilots had to land their plane as soon as possible wherever possible under unimagible circumstances. They all did it in a little over one hour, with no fatalities.
They are also heroes.
General Aviation (those Cessnas, Pipers, Beechcraft, Mooneys, Maules, Grummans, and the rest) was grounded as well. Many people fly for a living. While Air Transport pilots draw a salary, the flight instructor at your local airport are paid by the instruction-hour. Aside from teaching ground school, no fly = no pay. And the FBOs that rent the aircraft don’t make money when the aircraft are grounded. Some doctors use their own aircraft to get to dispersed places quickly. Some villages in Alaska depend on airplanes to bring supplies. Hunters are often in places only accessable by aircraft, and they were stranded. Even most Life-Flight helicopters were grounded. And those traffic reporters that help us work our way through gongested cities. Pipelines and power lines were left unpatrolled. Small cargo planes bring FedEx packages to your town and small aircraft transport cheques for banks. I’m not sure, but I think even the Civil Air Patrol was grounded.
People move near small airports, attracted by (initially) lower housing costs. Then they complain that there is an airport next to them and try to shut it down. They complain about “little aiplanes” (usually they call them “Piper Cubs” or “Cessnas” because that’s all they know – it’s like calling all cars “Fords” or “Chevies”) making noise. But most people have no idea of the economic impact General Aviation has on the country. When an earthquake hit San Francisco a few years ago (the Loma Prieta quake), emergency supplies were flown into an airport that residents had been trying to shut down. The Civil Air Patrol flew search dogs in to this airport in their Cessnas and Pipers. (The CAP likes the Cessna 182, but many members use their own aircraft with no compensation except for a small fuel stipend. The CAP does not cover costs of maintenance, insurance, tie-down, or the pilot’s time – all of which go into the operating cost of an aircraft.)
So in addition to the nation’s air carriers, and air carriers of other nations that were flying in our airspace, there are a great number of people who were at least inconvenienced and for the duration of the emergency lost their livelihood.