Types and Use of Airways
Airways are corridors established by a national government within its airspace to facilitate the navigation and control of air traffic under IFR conditions. Usually, an airway is 10 statute miles wide and follows a route over the ground defined by radio NAVAIDs.
Generally, there are many different airways within a country as evidenced by those established in the United States. In the United States, as well as in other countries, there are two sets of airways (one for low altitudes and one for high altitudes.) To distinguish one airway from another, each has its own designator, such as V (low altitude) and J (high altitude). These designators simplify the preparation of a flight plan and improve the communication between aircrews and air traffic controllers.
An alternate airfield is where an aircraft intends to land if weather conditions prevent landing at a scheduled destination. Occasionally, an airfield may also be identified as an alternate for takeoff purposes. This procedure is at the direction of company procedures and operations specifications that authorize the use of lower minimums for takeoff than for landing.
During flight planning, select certain airfields along the planned flight route as possible emergency landing areas and then annotate these airfields on the charts for quick reference. Consider the following factors when selecting an emergency airfield: type of aircraft, weather conditions, runway length, runway weight-bearing capacity, runway lighting, and radio NAVAIDs. The NOTAMs for these airfields should be checked prior to flight.
After the route has been determined, the navigator should study the area surrounding the planned route and annotate the highest obstruction (terrain or cultural). The distance within which the highest obstruction is annotated is in accordance with governing or local directives. The highest obstruction is taken into consideration when determining the minimum en route altitude (MEA) and in emergency procedures discussion.
Special Use Airspace
When determining the flight planned route, the locations of special use airspace has to be considered. The best way to find the locations of the areas is by checking an en route chart. After the route is determined, any special use airspace that may be close enough to the route of flight to cause concern (as per governing directives) should be annotated on the chart with pertinent information. Annotate time and days of operation, effective altitudes, and any restriction applicable to that area. These areas, when annotated on the chart, assist the navigator with in-flight changes and prevent planning a route of flight that cannot be flown.