None? Nobody puts airports inside city centers and metro areas don’t just have dense urban housing. The common solution in many land strapped cities is for airports to rout aircraft over water often by building airports on reclaimed land.
What generally gets areas in trouble is locations that used to be a good get worse as aircraft get larger and the surroundings get built up. The solution is to send larger airplanes to a new airport, but it’s not free and there’s no clear line when things get unacceptably dangerous.
What generally gets areas in trouble is locations that used to be a good get worse as aircraft get larger and the surroundings get built up. The solution is to send larger airplanes to a new airport, but it’s not free and there’s no clear line when things get unacceptably dangerous.