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10 Rare IFR Chart Symbols, And What You Should Know About Them

How many of these symbols do you recognize?

1) Stand-Alone AWOS/ASOS Weather Stations

Not connected to an airport, you'll find stand-alone AWOS and ASOS stations charted on enroute charts. They're common in places like the Colorado Rockies, where a few stand-alone weather stations have been installed to help you analyze localized mountain weather patterns.

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2) LF/MF Airways (Alaska Only + 1 In North Carolina)

LF/MF airways (airways based on LF/MF NAVAIDs) are sometimes referred to as colored airways because they are identified by color name and number (e.g., Amber One, charted as A1). Green and red airways are plotted east and west, and amber and blue airways are plotted north and south. Regardless of their color identifier, LF/MF airways are depicted in brown.

They're most commonly found in Alaska, but one still remains in the lower 48. It's called G13 and navigated off of the Manteo (MQI) NDB, located along North Carolina's coastline.


3) Helicopter RNAV Routes (TK Routes)

Two helicopter RNAV routes (TK-routes) exist in the northeast corridor between the Washington, DC, and New York City metropolitan areas. The TK-routes are for use by helicopters having IFR-approved Global Positioning System (GPS)/Global Navigation Satellite System (GNSS) equipment.


4) Cold Weather Corrections

In cold regions of the country, instrument approaches require cold weather corrections. It's your responsibility to make sure you know how to correct the altitudes, and which segments of the approach need to be corrected.


5) NDB-DME Stations

Ambler is an NDB-DME with both and NDB frequency of 403, as well as a DME channel of 108, both of which are listed on the enroute chart.


6) Crossing Altitudes By Compass Direction

The MCA (Minimum Crossing Altitude) is 8,400 MSL when flying south, as you can see on the chart.


7) Flight Services/NAVAID Name

This shaded box indicates that the flight service station and NAVAID have the same name.


8) Unusable Route Segments

Unusable route segments are charted when an airway is closed or no longer in use. They're a good reminder to pilots that may have frequently used the route that it is closed.


9) MEA Gap

If you're flying along this route at the MEA, you could lose ground-based navigational coverage along this segment of V134.


10) Crosshatch

If you find data on an enroute chart that has crosshatching, it indicates there's an abnormal status. To figure out why, you'll have to check the NOTAMs.


What other rare symbols IFR symbols did we miss? Tell us in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and an Embraer 145 First Officer for a regional airline. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), and is a former pilot for Mokulele Airlines. He's the author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.

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