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Each airway starts and finishes at a waypoint, and may contain some
intermediate waypoints as well. Waypoints use five letters (e.g., PILOX), and
those that double as non-directional beacons use three or two (TNN, WK).
Airways may cross or join at a waypoint, so an aircraft can change from one
airway to another at such points.
A complete route between airports often uses several airways.
Where there is no suitable airway between two waypoints, and using airways would result in a
somewhat roundabout route, air traffic control may allow a direct waypoint-to-waypoint
routing, which does not use an airway (often abbreviated in flight plans as "DCT").
Most waypoints are classified as compulsory reporting points; that is, the pilot (or the on-
board flight management system) reports the aircraft's position to air traffic control as the
aircraft passes a waypoint. There are two main types of waypoints:
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A named waypoint appears on aviation charts with a known latitude and longitude.
Such waypoints over land often have an associated radio beacon so that pilots can
more easily check where they are. Useful named waypoints are always on one or more
airways.
A geographic waypoint is a temporary position used in a flight plan, usually in an area
where there are no named waypoints (e.g., most oceans in the Southern Hemisphere).
Air traffic control require that geographic waypoints have latitudes and longitudes that
are a whole number of degrees.
Note that airways do not connect directly to airports.
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After takeoff, an aircraft follows a departure procedure (standard instrument departure,
or SID), which defines a pathway from an airport runway to a waypoint on an airway, so
that the aircraft can join the airway system in a controlled manner. Most of the climb
portion of a flight will take place on the SID.
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Before landing, an aircraft follows an arrival procedure (standard terminal arrival route,
or STAR), which defines a pathway from a waypoint on an airway to an airport runway,
so that the aircraft can leave the airway system in a controlled manner. Much of the
descent portion of a flight will take place on a STAR.
A - Z of Flight
July 2017
www.alliance-airways.net
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