Semi-Airborne Airport

Airplanes approaching an airport for landing usually approach at some shallow angle (3° if using ILS). This results in excessive aircraft noise experienced on the ground in the surrounding area, as well as a large area around the airport having to be controlled airspace, which is inconvenient for applications of drones within cities. Past proposals have suggested increasing the glideslope to mitigate this (i.e. delaying the start of the landing approach until closer to the airport, and descending more steeply).

I propose the opposite: Descend at a shallower angle— possibly even don't descend at all (well, maybe a couple of meters to go from above the runway to on the runway). Move the airport upward to meet the planes at some higher altitude instead.

It would be difficult to build a conventional building several thousand feet tall (and as wide as an airport plus all of the runways). I suggest supporting the airport buildings and runways on top of several fountain towers instead. The bases for these can be smaller in footprint, too, enabling use of the land between them for other purposes. (Also, at times of low usage, or if (part of) the airport is to be shut down for a while, it can be lowered to just above ground level and rest on top of the bases.) Guywires or similar may be necessary to keep the airport from being blown off station by the wind.

Additional benefits of detaching the runways from the ground are that they a) are repositionable, and b) don't have to be horizontal. Repositionable runways are obviously useful to enable increased utilization of runways with changing wind conditions (so you can have most of your runways aimed into the wind, regardless of the wind direction). Sloped runways would help with STOL and crosswinds. (To address the concerns at [3]: These runways would be capable of coordinating their motions with those of the airplanes, and if you need to do a go-around, there's no mountain in the way.)

To accomplish these features, the fountain base stations would need to be able to aim their pellet streams somewhat (and the vacuum tubes would need to be movable, and somehow accommodate a curved stream while the angle is changing, but that's doable). As well, there would need to be a horizontal component to actually move the runways around. I think that would be easiliest accomplished by winches on the guywires.

Passengers, cargo, employees, etc. are transported up and down between the ground and the airport by fountain elevators climbing the same fountains that support the airport buildings (fountains which will remain vertical at all times), possibly with additional angled fountains or guywires for stabilization. [1] Security, customs, etc. can be in a terrestrial building still, with only the terminal/runways being an airborne building.

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