thumb|This [[instrument flight rules chart shows low-altitude airways in the Oakland Area Control Center (near San Francisco, California).]]
Airways, air routes or flight paths are designated routes which aeroplanes fly to aid in navigation and help with separation to avoid accidents.
Airways are defined with segments within a specific altitude block, corridor width, and between fixed geographic coordinates for satellites navigation system, or between ground-based radio transmitter navigational aids (navaids; such as VORs or NDBs<!--(rare in the USA outside of Alaska)-->) or the intersection of specific radials of two navaids.
United States
In the United States, airways are defined by the Federal Aviation Administration (FAA) in two ways:
"VOR Federal airways and Low/Medium Frequency (L/MF) (Colored) Federal airways"
History
To guide airmail pilots on their delivery routes, the United States Postal Service constructed the first airways in the United States, the Contract Air Mail routes. These airways were between major cities and identified at night by a series of flashing lights and beacons which pilots flew over in sequence to get from one city to the next. Intermediate fields were located every in case of emergencies, with at least two landing strips a minimum of in length, and in width. Rotating airways beacons were erected every . However, these visual airways required the pilots to be in visual contact with the ground, which precluded flying in fog or clouds. Subsequently, the Department of Commerce funded the development of other means of airway navigation.
The first airways to be delineated by radio frequency were based on the old Low-frequency radio range also called the "Four Course Radio Range" or "A/N" system. The pilot listened for the stronger of the Morse codes transmitters ("· –" for "A" and "– ·" for "N", indicating left or right of the course); the objective was to be centered on course hearing a steady tone (the A and N Morse codes merge to form a steady tone when the receiver is equidistant from both transmitters).
Later airways were based on low/medium frequency ground stations, like the beat frequency oscillator (BFO) and the non-directional beacon (NDB). These L/M frequency airways were the colored airways. Colored airways still exist, mostly in Alaska. There are only a few colored airways remaining in the contiguous United States. There is one colored airway on the coast of North Carolina called G13 (Green 13). There is one Canadian colored airway designated A16 (Amber 16) that transits through US airspace in northwestern Washington State and is visible on the Seattle sectional chart. Additionally, there are several colored airways connecting to, and transitioning through, the Florida Keys. B9 (Blue 9) connects the Southern Florida mainland to Marathon Key. B646 (Blue 646) connects Mérida, Mexico to Nassau, Bahamas and transitions through the Florida Keys. A portion of B646 connects Key West to Marathon Key and serves as a bypass for aircraft unable to meet the 15,000 foot minimum altitude along that portion of V3. Finally, G765 (Green 765) connects Key West to Cozumel, Mexico. Colored airways are all depicted in brown on low and high altitude charts produced by the FAA's Aeronautical Navigation Products.
Boundary
Federal airways is defined to be wide and usually a floor of above the ground. It does not include the airspace of a prohibited area. Aerobatic flights are prohibited within federal airways.
Victor airways
Low altitude airways (below MSL) that are based on VOR stations, appear on sectional charts, world aeronautical charts, and en route low altitude charts and are designated with the prefix "V" (pronounced victor, hence, victor airways). Victor airways are usually assigned odd route numbers for north–south routes and even route numbers for east–west routes. Route numbers are listed serially if more than one airways share the same route segment.