A runway is a surface on an airport used for takeoffs and landings of aircraft. They are often made out of pavement, though other unpaved surfaces are used, such as dirt, sod, and gravel. They can be many different lengths, from 500m for STOL use to 11900m dirt runways at Edwards AFB.
Parts of a Runway
Runway Safety Area
Around the runway, there is a runway safety area, which is flat and mostly clear of objects. This is to make sure that there are no loose items on the ground near the runway that could impede aircraft using the runway.
EMAS (Engineered Material Arresting Systems)
See EMAS for the main article about this subject.
Often constructed at the beginnings and ends of runways are blast pads. These are to protect the runway and ground before it from jet blast produced by aircraft. If these blast pads are not there, terrain before the runway could degrade allowing the runway's surface to crumble towards it. When there are not areas at the ends of runways that are flat and smooth in case of overruns, such as at KMDW, these are often made into EMAS to help stop planes in overruns. They have yellow chevrons painted over them and are not suitable to land, take off, or taxi on unless emergency.
This is the beginning of the runway, from the blast pad to blast pad. There are normally a series of white lines, with the identification after that, to identify the runway, one on each end, in normal circumstances. Extremely rarely, in the case of EDDF, only one end is numbered, and because of this, this is the only used end. This threshold may be displaced from the start of the runway, see below.
Displaced thresholds displace the normal threshold from the beginning of the runway. These are often constructed due to the fact that aircraft cannot land at the beginning of the runway due to noise restrictions or pavement strength. There are arrows pointing in the direction down the runway on them, leading up to the threshold. Aircraft may use them for takeoffs and to end landings, but in normal circumstances, they are not to be landed on.
This is the main operational part of the runway. There are many markings on it, starting at the threshold and continuing down to the other threshold. There is a striped white line continuing down the middle of the runway, as well as landing zone markings. Landing zone markings start with two sets of 3 white stripes, each on one side of the runway. Farther down, there are two sets of solid white boxes, similar in size to the groups of three stripes. In some countries such as Canada and Britain, these are replaced with a different design of stripes. Ahead are two sets of two white stripes, two sets of two white stripes again, two single white stripes, and two more single white stripes. If aircraft do not touch down within this region often a touch-and-go is performed. It should be noted that some or all of these markings do not appear on smaller-sized airports or unpaved runways.
Almost all paved runways at major airports have lighting installed on them. This allows pilots to see the outline of the runway without actually seeing the runway, which helps for landing during night and low visibility situations. These lights use full-directional white lights to show the border and center line of the runway. Red lights point towards the middle of the runway and green lights point away from the runway from the threshold.
Approach lighting assists pilots with a higher-density array right before the threshold to assist in landings while the lights are on. Often on ILS enabled runways, there are two strips of lights continuing from the approach lights onto the runway through the the landing zone.
Instrument Landing System
See Instrument Landing System for the main article about this subject.
Often there are many devices built in under the pavement on runways. One of these systems is Instrument Landing System, or ILS. It uses radio signals to guide in a pilot who cannot perform a visual approach or wants a more precise approach, for any reason. This feature is included in FlightGear and is in use at almost all commercial airports, plus many general aviation ones.