In What is the number in a closed box right below a victor airway? I noticed:

enter image description here

What is an "Alternate Airway"?

  1. The radial value placement looks the same to me.
  2. The N suffix (after V2) is not an ICAO suffix.
  3. The AIM when searching for "Alternate Airway" comes up empty.
  4. The chart specifications (IAC 2) do not explain it.

Is it a leftover from something that used to exist? What is it?

(My gut feeling tells me it's something so obvious but I'm really not seeing it.)

  • 1
    $\begingroup$ It was not uncommon to have/use alternate Airways for enroute lateral separation between aircraft prior to the availability of radar. Note that the example shows a 15 degrees divergent angle which is the minimum lateral divergence. If you have 2 aircraft traveling in the same direction and one is assigned an alternate airway (15 degrees divergent) they will be laterally separated at 16 miles. (Table is in FAA Order 7110.65). ATC separation was developed non radar based and prior to radar traffic dictated more airway routes in certain locations. $\endgroup$
    – user22445
    Commented May 14, 2022 at 14:36
  • 1
    $\begingroup$ @757toga: would make for a great answer in addition to the existing one regarding its history! $\endgroup$
    – user14897
    Commented May 14, 2022 at 14:37
  • 1
    $\begingroup$ They are mentioned in the .65 2–5–1b: "Victor Twelve South." $\endgroup$
    – randomhead
    Commented May 14, 2022 at 15:29
  • $\begingroup$ @randomhead: thanks, I asked Bianfable to add it and it's now in the answer. Maybe a really old revision would have an actual explanation for the term. $\endgroup$
    – user14897
    Commented May 14, 2022 at 16:09
  • $\begingroup$ An alternate airway is provided by a tracheotomy. $\endgroup$ Commented May 15, 2022 at 13:28

3 Answers 3


I found an old definition in the All-Weather Flight Manual published by the US Navy in 1957:

Alternate Airways

Alternate airways are occasionally used for lateral separation when traffic conditions require it. The alternate airways are located not far from the associated main airway but are at least 15° on either side, or both sides, of the main airway. The alternate airway number includes the main airway number, plus an indication of the geographic position in which it lies with respect to the main airway. V-20-S is the alternate airway south of Victor 20. Your clearance will include Omnirange stations which form any particular alternate airway so that you will have no doubt when using an alternate airway.

The current AIP Appendix: ATS Routes does not list any alternate airways as far as I could find, so I guess they are not used anymore. They are however still mentioned in FAA Order JO 7110.65:

b. VOR/VORTAC/TACAN alternate airways. State the word “Victor” followed by the number of the airway in group form and the alternate direction.

EXAMPLE- "Victor Twelve South."

(FAA Order JO 7110.65 2-5-1)


Thanks to @757toga's comment, I was able to find more:

Circa mid-80s the FAA agreed with ICAO to "revoke all Alternate Airways" (Federal Register Vol. 51, 1986), and for example in 1986 was in the process of renaming such an airway in Hawaii.

And before that, from a related study of the NAS (National Airspace System):


Study Date: November 8, 1982. (2 weeks)

The present alternate airway structure is still based largely on nonradar separation standards. With the increased use of radar, a study is needed to evaluate the possibility of eliminating unnecessary alternate airways and reidentify remaining routes taking into consideration ICAO standards. This would also contribute to a reduction in chart clutter.

— ADA150743 National Airspace Review Enhancement Plan. Revision 3. 1984. (PDF misfiled under ADA159743)


To add to the information from the other answers to this question:

Years ago, prior to the extensive availability of ATC radar, it was not uncommon to use Alternate Airways for IFR enroute lateral separation between aircraft .

In order to achieve and maintain separation between aircraft in a non-radar environment ATC procedures could be complex and inefficient (compared to the use of radar separation). One procedure that reduced the complexity was the use of Alternate Airways. These airways were located in areas where, based on the traffic flow, were beneficial for both ATC and pilots.

For example, consider if one aircraft is at a higher altitude than a second aircraft and they are in close proximity and assigned the same (Victor Airway) route. If the aircraft at the higher altitude needs to descend to an altitude below the second aircraft some form of non-radar separation (longitudinal or lateral) needs to be achieved prior to allowing the aircraft at the higher altitude to descend. One method to achieve this as efficiently as possible was the development and use of alternate airways. (see the sample image below for an example)

If the angle between the primary Airway and its alternate was 15 degrees the point at which ATC lateral separation would exist would be 16 NM from the Navaid. If the angle between the primary Airway and its alternate was greater than 15 degrees the point at which lateral separation would exist would be less than 16 NM. (see FAA Order JO 7110.65Z, Section 5, Lateral Separation Non-Radar)

The image below is just one example of the use of Alternate Airways, which likely no longer exist anywhere in the U.S. due to the availability of radar throughout most of the enroute structure.

Lastly, the foundational design of the IFR ATC system was (and is) based on Non-Radar routings and loss of communication between ATC and pilots (with some exceptions). The elimination of Alternate Airways is a product of the now expansive availability of ATC radar coverage resulting in the reduced need for using Non-Radar separation (longitudinal and Lateral) procedures. (Vertical separation is Non-Radar separation even when used in a radar environment)

enter image description here


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