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On this Garmin GMA 340:

  • the outer marker is blue and is designated O
  • the middle mark is amber and is designated M
  • the inner marker is white and is designated A and placed on the far left.

I looked at the GMA 340 Manual and could not find an answer although it does say Airway/Inner Marker.

Why would it say Airway if this is what the A indeed stands for and why even have an inner marker because that Garmin can't do a Category II approach?

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  • $\begingroup$ It was a typo yes, thank you. $\endgroup$
    – jskypilot
    Mar 17, 2016 at 15:26

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The "A" is not an inner marker. The A is an airway marker. Airway markers were part of a now-obsolete system of "red" airways. They were placed along the enroute path and they could be picked up at cruise altitudes. The red airway system was mostly abandoned in the 60's and few "A" markers are still operational. Here's a map showing where they were located. They weren't at aerodromes. red airway beacons Source

The airway markers transmit the same 3000 Hz audio frequency as inner markers so the airway marker can be used to pick up the inner marker. Since you say that unit is not certified for cat II it makes sense that they labeled it "A" instead of "I" although it can be used for inner markers.

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    $\begingroup$ red airways are not obsolete: aviation.stackexchange.com/questions/11737/… $\endgroup$
    – rbp
    Mar 17, 2016 at 15:33
  • $\begingroup$ @rbp Ah so. I'll correct. Somebody should correct Wikipedia too. Aside from Alaska and Florida are they still used elsewhere? And are the beacons still operational? $\endgroup$
    – TomMcW
    Mar 17, 2016 at 17:01
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You have mentioned that outer marker is designated as B which is not. It is 'O'. Now the question is if O is outer marker and M is middle marker then what is indicated by A? A serves two purpose, Inner/ Airway marker. So A does not indicate only Airway marker. The airway marker was used to indicate reporting points along the center line of now obsolete "Red" airways which Tom McW mentioned.

This was sometimes a "fan" marker, whose radiated pattern was elongated at right angles across the airway course so an aircraft slightly off course would still receive it. Please do not confuse about fan marker, The term fan marker refers to the older type of beacons used mostly for en-route navigation. Most of these are obsolete now a days. There are uses of marker beacon on the instrument approaches mainly.

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  • $\begingroup$ Yep, I should have typed O. Thanks for the correction. Thank you for the added info about airway/inner markers. $\endgroup$
    – jskypilot
    Mar 17, 2016 at 15:28

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