from The New Book of Knowledge®
An airport is a place where airplanes land and take off. At an airport, passengers and cargo are picked up and dropped off, and airplanes are refueled and serviced.
The first airplanes were small and light and needed only an open, flat area to take off and land. For this reason, and because very few people traveled by air, an early "airport" often consisted of only an unpaved landing field and a hangar, a large building in which airplanes are housed and repaired.
Since those early days, flight has become an important means of transportation, and aviation is now a major industry. Today, there are some 36,000 airports of all sizes throughout the world (including nearly 20,000 private airfields). Airports, like airplanes, have become much larger and more complex. In fact, airports in major cities are often so large that they can almost qualify as cities themselves. These large air carrier airports handle thousands of flights every day, mainly those of scheduled airlines. They are especially well equipped to accommodate large, jet-engine airplanes.
The vast majority of airports, however, are not as large as the air carrier airports. For example, of the more than 5,300 public airports in the United States, only 8 percent are large enough to handle commercial flights. Most airports are equipped to handle mainly smaller, propeller-driven airplanes owned by businesses or private citizens. Airports that handle this type of airplane and not those of scheduled airlines are known as general aviation airports. If a small airport is located near a much larger airport, the small airport is likely to assume a large share of the area's small-airplane traffic and is known as a reliever airport.
Although smaller airports are more numerous than large ones, most air travelers—roughly 425 million per year in the United States alone—begin and end their journeys at a large airport.
A Trip Through a Large Airport
Your first stop at the airport depends on the means of transportation you have used to get there. You can travel to some airports by train or bus, while others can be reached only by taxi or private car. If you have driven your own car, it must be parked in an airport lot or garage, which may have up to 20,000 parking spaces. From there you may have to board a shuttle bus to take you to your next destination, the terminal.
The terminal building or buildings are the largest at the airport and are the center of many services and activities. All passengers must pass through a terminal when boarding or leaving an airplane. When you arrive at the terminal, you will first go to the airline ticket counter. There, in exchange for your ticket, the airline agent will give you your boarding pass, which gives you permission to sit in a specific seat on the airplane.
The airline agent will attach a cardboard label to your baggage. The label has an identification number that matches one that is stapled to your boarding pass. The label also has a three-letter code, which identifies the airport at which you will land and helps the airline baggage handlers get your bags to the correct airplane. Your baggage will then travel on a conveyor belt into the underground "belly" of the airport. On international flights and some domestic flights, the baggage will be checked for weapons. A baggage handler will load all the baggage for your flight onto a cart, drive the cart to the airplane, and load the baggage onto the plane.
While you wait to board your plane, there may be time to visit some of the many shops located in the terminal. These include banks, newsstands and bookstores, restaurants and snack bars, and gift shops. Most international airports also have duty-free shops. If you are visiting a foreign country, you can buy goods at the duty-free shop and bring them home without having to pay duty, or import tax.
Some airports have an observation lounge, where large windows allow you to watch airplanes take off, land, and taxi (move slowly along the ground) to a gate. Gates are the points from which passengers leave the terminal and board the airplane.
Before heading to your gate, you will be screened by an electronic device that detects hidden weapons. Any bags that you are carrying on the plane will be passed through an X-ray machine to be sure they do not contain any weapons. These security checks are necessary to prevent the airplane from being hijacked.
The next stop is your gate, where your airplane is waiting. The distance between the main part of the terminal and the gate may be too far to walk. In some airports, you will have to take a quick train ride. In others you will take a shuttle bus to a "mid-field" terminal, which is separate from the main terminal. In still other airports, passengers are transported to their gates on moving sidewalks. When you reach your gate, you will find yourself in a large, open waiting room. From here you will board your plane, most likely via a short, covered walkway.
Airplanes take off and land on the runway. Jet planes require very long runways, sometimes as much as 2 miles (3 kilometers) in length. An air carrier airport typically has between two and four runways and may have as many as eight. A runway may look like an ordinary paved road. But, unlike roads built for cars, runways are made of special material able to withstand the impact of 830,000-pound (375,000-kilogram) airplanes. The runways will not crack under extreme cold or heat. Snowplows and salt spreaders keep them clear and ice free in winter. Drainage systems keep them from being flooded during rainy weather. Emergency fire and ambulance crews are always on duty.
The roads that run alongside the runways are called taxiways. They link the runways with the terminal and with other airport buildings, such as storage and service hangars. Lining the runway is a complex system of lights and signs with numbers and letters, which guide pilots in taking off, landing, and taxiing to and from the gates. Pilots are also guided by the ground crew, who steer airplanes into their gate parking positions. (Because airplanes cannot back up, they are often towed out of their gates by trucks.)
Air Traffic Control
Before the pilot can take off, or even start the plane's engines, permission must be given by the airport control tower. The control tower is the nerve center of the airport. From there, all approaches, landings, and takeoffs are directed by radio contact with the pilot. Air traffic controllers, the men and women in the control tower, are skilled at helping as many as 100 planes per hour take off and land without a collision. To do their job, they rely on sophisticated computers and communications systems. In the United States, air traffic controllers are employees of the Federal Aviation Administration (FAA).
Air traffic controllers in charge of ground control tell the pilot when to start the engines and which taxiways and runway to use. After clearance (permission to take off) is given, the tower gives the pilot instructions to get clear of the airport area and proceed on course. Throughout the flight, the pilot must report at regular intervals to air traffic control centers located along the flight route. The pilot may be directed to change course or altitude to avoid bad weather or other air traffi