Airports

Airports are among the busiest transportation centers. In the United States, over 500 airports provide airline passenger service to about 500 million people each year. These airports also handle about 9 million metric tons of air cargo annually. Canada's 26 airports in its national airport system provide service to about 60 million passengers each year. The total annual economic impact of U.S. airports is estimated at $575 billion. This value includes the price of airfares purchased by passengers, the salaries of airline and airport employees, taxes, and indirect earnings from related businesses and industries. Airports are so important economically that many companies will not locate factories or offices in cities that do not have an adequate airport. The busiest commercial airports in the world are William B. Hartsfield International Airport in Atlanta, Georgia; Chicago-O'Hare International Airport in Chicago, Illinois; Los Angeles International Airport in Los Angeles, California; Dallas/Fort Worth International Airport, near Dallas, Texas; and Heathrow Airport in London, England.

Commercial airports are designed to transfer passengers and freight to and from aircraft. In order to accomplish this transfer as efficiently and as safely as possible, airport operations are grouped into four general areas: aircraft services, passenger and freight services, support services, and airport security.

Ð'* Aircraft services focus on the flight, maintenance, and refueling of aircraft at the airport, as well as on air traffic control around the airport. They are also in charge of providing an adequate runway.

Airport runways are arranged to permit the maximum number of safe takeoffs and landings in all weather conditions. Runway designs at airports differ according to the type of aircraft the runway serves, the prevailing wind direction and speed, and the availability of land. Environmental factors such as nearby wildlife or obstructions to navigation such as mountains and tall buildings must also be considered when building runways.

The control tower is a usually a tall structure located at or near the terminal. It manages all air traffic at the airport. The tower is centrally located and elevated so that an unobstructed view of the airport can be maintained from the tower at all times. Controllers inside the tower issue taxiing instructions to guide aircraft both to and from the runways and ensure that aircraft do not land or take off until the runways are clear. At larger airports, smaller additional towers are staffed by airline employees who control the ground operations of the airlines they work for. The airline tower staff manages the flow of ground vehicles and aircraft in the immediate vicinity of the terminal building. It also coordinates baggage, fuel, and food service. Other airline employees provide pilots with final flight information, such as the passenger list and the latest weather information.

Ground crews working on the apron area near the gates help maintain aircraft in between flights. They load baggage, restock food and other supplies, perform routine maintenance, and refuel aircraft. Fuel is normally stored in large tanks above ground and transported to aircraft either by underground pumping facilities or by refueling trucks. Repair facilities range from small facilities housed in a single hangar to large complexes that employ thousands of trained maintenance technicians. In cold climates, ground crews also work to keep runways and aircraft free of snow and ice.

Ð'* Passenger services are centered in the terminal building, where passengers purchase tickets, load and retrieve baggage, and enter and exit aircraft.

All major terminals provide the same services, but a terminal can be organized in several different ways. The four different types of terminals are gate arrival, pier, satellite, and transporter. Each type connects passengers with aircraft in different ways.

Gate arrival terminals are rectangular buildings that have aircraft parking on one side and have motor-vehicle parking as well, often on the opposite side of the terminal. Simple gate arrival terminals are the most common type of terminal found at small airports. Aircraft simply park alongside the terminal, and passengers walk across the apron to board the aircraft. Large commercial airports use gate arrival terminals also. At most commercial airport gate terminals, such as at Dallas/Fort Worth International Airport, aircraft pull up directly to the terminal at predetermined areas called gates. Flexible covered pathways called airbridges connect the gate to the aircraft and allow passengers to board and exit the aircraft.

Pier terminals have piers that extend outward like arms from a central building and provide boarding gates on both sides of each pier for its entire length. Each pier is known as a concourse. Pier terminals provide efficient use of space, since common facilities can be located in the central building instead of at each gate. If a given airline has use of nearby gates, or an entire pier, then passengers transferring to other flights may not have far to walk. Pier terminals are in use at Los Angeles International Airport, Heathrow Airport in London, and Toronto International Airport in Toronto, Ontario, Canada.

Satellite terminals also provide common facilities at a centralized building. However, passengers need not walk the length of a pier. Instead, transportation to gate areas is provided by buses or by automated rail systems such as people movers. Satellite terminals are often circular in layout and provide aircraft parking around their entire perimeter. They have many of the same characteristics of pier terminals. Satellite terminals are in use at Houston Intercontinental Airport in Houston, Texas, and Orlando International Airport in Orlando, Florida.

Transporter terminals use a common building for the processing of passengers, who then board specialized vehicles known as mobile lounges that ferry passengers directly from the gate to the aircraft and back. Dulles International Airport in Washington, D.C., pioneered this concept. Transporter terminals work well for passengers on direct flights but are inconvenient for passengers who are transferring to other flights, since they cannot simply walk to their connecting aircraft's gate. Nevertheless, the flexibility of transporter terminal systems has made them popular at airports that have experienced rapid growth. The operators of such airports often find it easier to drive passengers to parked aircraft than to build an expensive new terminal. Since most airports were built decades ago, the majority of terminals have been modified and expanded as the airports have grown. Many airports use