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Route String Parser

This topic provides you with an overview of the route string parser. 

The route string parser takes advantage of fixed radials and airway intersections allowing for much greater route flexibility

Route strings can be composed of a number of variables. The variables that can be used are:

  • Airport

  • Waypoint

  • Named airway

  • Radial airway

  • Special airway (e.g., MTTA, MTT, DCT, MTTH, ... , etc.)

  • SID name

  • STAR name

  • Track Origin (e.g., NAT-A, PAC-K, NOR-5, etc.)

  • Preferred Arrival

  • Preferred Departure.

Note: A space between waypoints implies a direct segment (DCT) between them.

MTTA Expansion Options

The following is a list of options that can be used with MTTA when generating a route.

  • MTTA@350: Do MTTA at the requested flight level FL350

  • MTTA@250-330: Do MTTA with a requested flight level range of FL250 to FL330

  • MTTA@MIN-330: Do MTTA with a requested max flight level of FL330 (no imposed minimum so the published minimums are used)

  • MTTA@250-MAX: Do MTTA with a requested min flight level of FL250 (no imposed maximum so the published maximums are used)

  • MTTA:CDR3: Allow airways marked as CDR3 in menu 341 (airways).  There are very few like this, as most are now controlled by rules, and this flag does not affect rules.

  • MTTA:CDR2@330: Allow airways marked as CDR2 in menu 341 (airways) and do the MTTA at FL330. Note: This has no effect as there are no airways marked as CDR2 in menu 341. Most CDRs are now controlled by rules and this flag does not affect rules.

Fixed Radial Segments

  • commonly referred to as a radial.
  • a combination of an existing waypoint or fix (typically a VOR), and a heading that travels from that location. 
  • The convention for naming the radial is the VOR location followed by the degrees from 0° (north).


Terminating at a Fix

  • When a radial has an endpoint that is a fix
  • the radial is considered to be more than a named direct leg.
Below picture illustrates a radial terminating at a fix. 
Note: The applicable route string portion would be FOO FOO135 BAR.


Terminating at an Airway

Some radials will terminate at an airway, at a point between two fixes


Illustrated below, the radial terminates when it intersects airway J500. 

Note: The applicable route string portion in this case is FOO FOO135 J500 QUX, since the route continues on J500 after the intersection towards QUX.


Terminating at Another Radial

Radials can also terminate by intersecting another radial from a different fix. In such a case, both fixes and radials are used in the portion of the route string.



The applicable route string portion for the example is FOO FOO135 BAR270 BAR.


Route String Expansion Examples

You can add NO_SIDS or NO_STARS to avoid SIDs and STARs and generate a direct route to the most efficient enroute waypoint.

Allow the user to input a radial/dme fix in the Route String combination box

The user can manually input a radial/dme fix in the route string field of the route screen as well as FOMS Menu 305

The format wwwrrrddd will be used:

  • www is the VOR Ident, 
  • rrr is the bearing in magnetic degrees, 
  • ddd is the distance in nautical miles. 

FRD points will persist and be reported in that format on ATC filings and flight plans. Note: These will not be converted to lat/lon positions. Use of pure lat/lon remains unchanged.



Flight Level example

The route string can also describe altitude flight level requests. This can be:

  • Request at a specific altitude with @XXX (flight level in hundred feet)     

    • E.g.: J501@300 (fly airway J501 at level 300 [30,000 feet])

  • A requested flight level range with @XXX-YYY (flight levels in hundred feet)

    • E.g.: J501@300-400 (fly airway with a minimum flight level of 30,000 feet and a maximum flight level of 40,000 feet)

    • E.g.: J501@MIN-400 (fly airway with no minimum flight level and a maximum flight level of 40,000 feet)

    • E.g.: J501@300-MAX (fly airway with a minimum flight level of 30,000 feet and no maximum flight level)

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