P: Commercial Service - Primary are publicly owned airports that receive scheduled passenger service and have more than 10,000 passenger boardings (enplanements) each year. Each primary airport is sub-classified by the FAA as one of the following four "hub" types:
L: Large Hub that accounts for at least 1% of total U.S. passenger enplanements.
M: Medium Hub that accounts for between 0.25% and 1% of total U.S. passenger enplanements.
S: Small Hub that accounts for between 0.05% and 0.25% of total U.S. passenger enplanements.
N: Non-Hub that accounts for less than 0.05% of total U.S. passenger enplanements, but more than 10,000 annual enplanements.
CS: Commercial Service - Non-Primary are publicly owned airports that receive scheduled passenger service and have at least 2,500 passenger boardings each year.
R: Reliever airports are designated by the FAA to relieve congestion at a large commercial service airport and to provide more general aviation access to the overall community.
GA: General Aviation airports are the largest single group of airports in the U.S. airport system.
Enpl. - The number of enplanements (commercial passenger boardings) that occurred at the airport in calendar year 2019, as per FAA records.
