h a l f b a k e r y
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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 : These runways would be capable of
coordinating their motions with those of the airplanes,
if you need to do a go-around, there's no mountain in the
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
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. 
Security, customs, etc. can be in a terrestrial building
still, with only the terminal/runways being an
Mentioned in idea. Prior art (which turns out to not be my own) [notexactly, Oct 24 2016, last modified Oct 27 2016]
Prior art [notexactly, Oct 24 2016]
Prior art and concerns [notexactly, Oct 24 2016]
Fulton recovery system
A "kick in the pants", apparently... [neutrinos_shadow, Oct 25 2016]
||Landing weight of a typical LCA, maybe 100,000 kg.
||Now, you can't just "fly" a big plane onto a runway. You have to dump speed, and activate drag-inducing high-lift devices, or you'll burst the tyres. The glideslope's a function of sink rate and airspeed, not that amenable to tinkering, because if you go too low or too slow there's no quick way of recovering with a turbofan.
|| How much noise will the fountains make ?
||How much energy will they use ?
||How fast can the control system react to an extra 100 tons of load dropping down on it ?
||I know that technology was developed to allow a
person to be picked up by a passing aircraft,
its having to land. Presumably the same
could be used to drop passengers off, as well,
the plane stays safely away from the ground.
||In fact... OK, I've got the disembarkation figured
out. You just need a tail-ramp on the plane, a
large pod in which the passengers can stand, and a
drogue chute. For picking passengers up, you
could do exactly the same thing, only in reverse
and using a different system.
||[MaxwellBuchanan]; I believe you are thinking of the Fulton recovery system (linky).
||The problem with an airborne airport is you need some way, prehaps an aircraft, to get to it. Then that aircraft would need an airport. Before long, you end up with a stairway of airports...
||That'd be a good idea from an ecological point of view - the
aircraft needn't use any fuel by going anywhere, they could
remain immobile and stationary in the air on the apron of
the airborne airport, and you could simply walk through the
successive network of airports and aircraft to get to your
destination. Without your luggage.
||[+] only because of so much half-baked prior art ...