# 10.3.1: ATS routes


A route is a description of the path followed by an aircraft when flying between airports. A complete route between airports often uses several airways connected by waypoints. However, airways can not be directly connected to airports. The transition from/to airports and airways is defined in a different way as we will see later on. Thus, the network of ATS routes refer only to the en-route part of the flight (excluding operations near airports).

## Airways

Figure 10.8: Air navigation chart: VOR stations as black hexagons (PPM, DQO, MXE), NDB station as brown spot (APG), VORNAV intersection fixes as black triangles (FEGOZ, BELAY, SAVVY), RNAV fixes as blue stars (SISSI, BUZIE, WINGO), VORNAV airways in black (V166, V499), RNAV airways in blue (TK502, T295), and other data. Author: User:Orion 8 / Wikimedia Commons / Public Domain.

An airway has no physical existence, but can be thought of as a motorway in the sky. In Europe, airways are corridors 10 nautical miles (19 km) wide. On an airway, aircraft fly at different flight levels to avoid collisions. The different flight levels are vertically separated 1000 feet.11 On a bi-directional airway, each direction has its own set of flight levels according to the course of the aircraft:

• Course to the route between $$0^{\circ}$$ and $$179^{\circ}$$: east direction $$\to$$ Odd flight levels.
• Course to the route between $$180^{\circ}$$ and $$359^{\circ}$$: west direction $$\to$$ Even flight levels.

Each airway starts and finishes at a waypoint, and may contain some intermediate waypoints as well. Airways may cross or join at a waypoint, so an aircraft can change from one airway to another at such points. A waypoint is thus most often used to indicate a change in direction, speed, or altitude along the desired path. Where there is no suitable airway between two waypoints, ATC may allow a direct waypoint to waypoint routing which does not use an airway. Additionally, there exist special tracks known as ocean tracks, which are used across some oceans. Free routing is also permitted in some areas over the oceans.

## Waypoints

A waypoint is a predetermined geographical position that is defined in terms of latitude/longitude coordinates (altitude is ignored). Waypoints may be a simple named point in space or may be associated with existing navigational aids, intersections, or fixes. Recently, it was typical that airways were laid out according to navigational aids such as VORs, NDBs, and therefore the position of the VORs or NDBs gave the coordinates of the waypoint (in this case, simply referred to as navaids). Nowadays, the concept of area navigation (RNAV) allows also to calculate a waypoint within the coverage of station-referenced navigation aids (VORs, NDBs) or within the limits of the capability of self contained aids, or a combination of these. Waypoints used in aviation are given five-letter names. These names are meant to be pronounceable or have a mnemonic value, so that they may easily be conveyed by voice.

## ATS routes network

Summing up, the complete network of routes formed by airways and waypoints is referred to as ATS routes. The ATS routes are published in the basic manual for aeronautical information referred to as Aeronautical Information Publication (AIP). AIP publishes information for en-route and aerodromes in different charts (the so-called navigation charts), which are usually updated once a month coinciding with the Aeronautical Information Regulation and Control (AIRAC) cycle. Ocean tracks might change twice a day to take advantage of any favorable wind.

11. This only applies up to 41000 ft., where the separation increases to 2000 ft.

10.3.1: ATS routes is shared under a CC BY-SA 3.0 license and was authored, remixed, and/or curated by Manuel Soler Arnedo via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.