Curious about the answer to this question: How may I verify WAAS channel number on G1000?, I just found that SBAS/WAAS use in aviation seems to be poorly explained.

In particular the WAAS "channel number" seems to suggest that some radio frequency is associated with a given WAAS approach.

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(Image taken from the linked question)

I think the WAAS service is provided by only two geosynchronous satellites, each one broadcasting on the same frequency the corrections for the whole US area. So there is no need to tune the WAAS receiver based on the airport location, the runway number, or the LPV identifier.

So the question: Are these 3 informations strictly redundant (maybe not taking into account version numbers), and they exist only for triple-check purpose?

  • LPV approach name: RNAV (GPS) Y RWY 36L,
  • WAAS channel number: WAAS CH 56613,
  • WAAS approach ID (aka reference path identifier): W36A

Could you confirm that selecting any of these values on the avionics will only change what is retrieved from the local navigation database, and will not impact the GPS/WAAS data received?

Note: I could understand if the approach were LAAS/GBAS (local ground-based) instead of SBAS.

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    $\begingroup$ The channel number is one way of selecting or confirming the correct approach has been loaded. It was the original intent to just type in the channel number to select the approach. Avionics manufacturers didn't like that approach. $\endgroup$ – wbeard52 Dec 20 '15 at 19:27
  • $\begingroup$ -1 you didn't seem to read the airman's information manual reference from the question you quoted which clearly explained the "channel number" meaning. $\endgroup$ – Steve H Dec 20 '15 at 23:18
  • $\begingroup$ It was in 2 places, the link you found and listed was one: forums.jetcareers.com/threads/… - and the comment I made to the question that initially prompted you to ask this one supplied the AIM reference too. Maybe there is sufficient abiquity in the AIM that you still have it as a question. But heck, +1 for asking for clarity. $\endgroup$ – Steve H Dec 20 '15 at 23:37

This pdf by Jeppesen provides the meaning:

WAAS Channel Number, unique to each airport, and Reference Path Indicator (RPI), which is made up of the letter “W” plus two or three characters representing the runway number. These are shown in both the Briefing Strip (chart heading) and plan view.

So the Channel Number provides the airport, and the RPI provides the runway number as well as the specific procedure. The combination of the two of them provides a specific approach at a specific airport, in much the same way that the title of the procedure on the approach plate is only meaningful if you combine it with the airport identifier.

As far as what you need to select in a particular avionics package, that depends on the design, but you are correct that it doesn't affect how it processes the GPS / WAAS signals.

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    $\begingroup$ Why the two procedures on the linked question have a different channel number while they are for the same airport? $\endgroup$ – mins Dec 21 '15 at 0:16
  • $\begingroup$ @mins Excellent question, I checked the most current version of the charts and they are different too. Doesn't seem to be consistent with what Jeppesen says... $\endgroup$ – Lnafziger Dec 21 '15 at 4:41

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