14 CFR 398.2 - Number and designation of hubs.
(a) What is a hub? The Department considers hubs as belonging to any one of three classifications:
(1) A large hub is a place accounting for at least 1.00 percent of the total enplanements in the United States;
(2) A medium hub is a place accounting for at least 0.25 percent but less than 1.00 percent of the total enplanements in the United States; and
(3) A small hub is a place accounting for at least 0.05 percent but less than 0.25 percent of the total enplanements in the United States.
(b) How many hubs? (1) As a general matter, the Department will require service to one large or medium hub.
(2) In Alaska or when the nearest large or medium hub is more than 400 miles from the eligible place, the Department may instead require service to a small hub or nonhub.
(3) In some cases, the Department may require service to two hubs, of which at least one will be a large or medium hub. The Department will require service to two hubs if an eligible place has close commercial, geographic, and political ties to both hubs and if there is sufficient traffic from the eligible place to support two round trips a day to both hubs. If traffic is not sufficient, the Department may require one round trip a day to both hubs if the community requests such service.
(4) In no event will essential air service consist of service to more than two hubs.
(c) Which hub? (1) In designating hubs, the Department will weigh all of the following factors:
(i) The extent to which candidate hubs provide access to the national air transportation system;
(ii) The commercial, geographic, and political ties of candidate hubs to the eligible place;
(iii) The traffic levels to candidate hubs, as shown by traffic studies and origin and designation data;
(iv) The distance of candidate hubs from the eligible place; and
(v) The size of candidate hubs. Large size will be a positive factor, but principally as substantiating the access and community-ties factors.
(2) For Alaska, rather than requiring service to a hub, the Department may instead require that service from an eligible place be provided to a nearby focal point for traffic which, in turn, has service to a hub.