Airports, Air Traffic Control, and Airspace

Controlled
As their name implies, controlled airports have some sort of control exercised over them, typically a control tower. Pilots are required to maintain two-way radio contact with the control tower, while operating within the airspace of the airport. When arriving at controlled airport, it is recommended that pilots contact the control tower roughly 15 miles from the airport. When leaving the airport, once clear of the airspace, pilots do not need to request permission to leave the frequency of the tower. When arriving to land at a controlled airport, the tower controller will, when necessary, issue clearances for aircraft to enter the desired traffic pattern, as well as proper taxi clearances when on the ground.

Uncontrolled
Uncontrolled airports are airports which have no control tower, or no currently operating control tower. At uncontrolled airports, no radio communications are legally required, they are strongly encouraged by the Aeronautical Information Manual. At these airports, pilots are advised to communicate on the Common Traffic Advisory Frequency (CTAF). The CTAF for an airport may be a Unicom, a Multicom, FSS (Flight Service Station) or even the closed control tower frequency. Pilots are advised to communicate as appropriate on the designated CTAF frequency for an airport 10 miles from the airport. Recommended radio calls include entering downwind, base, and final, as well as leaving the runway.

Runway Layout
Runways are often built so that they allow for operations during conditions in which prevailing winds for the location occur. This can be as simple as a single runway, pointing in the direction of typical winds, to complex arrangements of crossing runways, for various wind conditions. Runways are labeled with 2 numbers, corresponding to their magnetic heading. To find this 2 number heading, take magnetic heading, round to the nearest 10, and drop the last digit. For instance, a runway showing a 36, would roughly be orientated at 360° magnetic. Runways are a straight line, so thus, the opposite end of the same runway would be runway 18. Airports with parallel runways will have them designated into Left, Center and Right, if applicable. For instance Chicago Midway has runways 31L, 31C, and 31R.

Airport Traffic Patterns
Airport traffic patterns are set procedures for use in airports allowing for a smooth flow of traffic in and out of an airport. The traffic pattern consists of six parts.

The Upwind Leg is the flight path parallel to the landing runway, in the direction of intended landing.

The Crosswind Leg is the flight path at right angles to the landing runway, off its takeoff end.

The Downwind Leg is the flight path parallel to the landing runway opposite the direction of intended landing.

The Base Leg is the flight path at right angles to the landing runway off its approach end.

The Final Approach is the flight path in the direction of landing along the extended runway centerline.

The Departure Leg is the flight path which begins at takeoff and continues ahead until 1/2 mile beyond the runway, and 700 above ground level.

Airport Markings
Airport markings help guide pilot navigation their plane through the airport. They are used as a navigational aide.

Markings can be found on taxiway, runways and airport ramps, as well as on other areas of the airport property.

Minimum requirements for runway marking depend on the approach category of each runway. Approach categories include: Visual Approach runways are required to have threshold markings if they serve category C and D airplanes.
 * Visual Approach
 * Non-precision Approach, and
 * Precision Approach

Air Traffic Control
Aerodrome is a defined area on land or water including any building, equipment and installations, intended to be used either wholly or in part for the arrival, departure and surface movement of aircraft.

This is an ICAO standard definition from icao doc 4444 air traffic management (ATM).