"Much better to land airplanes in airports, rather than trying to catch with enormous nets."
Airports are the ninth Land Industry, and produce Nuclear Plants. Airports require 30 B Nuclear Plants to unlock and the base cost of one Airport is 10 AA Nuclear Plants, 10 MMM Land, and 2 Comrades.
Airports are also featured in the Supreme Vehicle Show event, where it's tier 1 of the Fuel Industry.
The first rank with a mission requiring Airports is Rank 67, and Airports can be automated with the researcher Maverick Ryback starting at Rank 68.
Although Airports only require 3 times as many Comrades to unlock as Nuclear Plants, Airports cost a large amount of Nuclear Plants and Land and thus can be seen as a difficulty spike that will require researcher upgrades if one does not want to wait a week to build up enough Land to afford many of them every rank.