THE WAAS CHANNEL.

Have you ever wondered what does the channel numbers on the SBAS approach charts stand for?

When you select a PBN approach, we find WAAS approach type in United States, or EGNOS in Europe, amongst others. Below the approach procedure designator, i.e. RNAV (GPS) Y 04L in KJFK, a WAAS with CH 77519 appears underneath. Just below channel numbers there is a combination of letters and numbers.

If we remember, WAAS is system which augments GPS signal in other to improve GPS position. To do that, a geostationary satellite system broadcast a correction signal to aircraft. In U.S.A is WAAS. Then, it’s not necessary to place any ground station at airports to broadcast this correction signal to correct aircraft GPS position like in GBAS system. But why there is a channel on the approach chart though?

When the system was designed, the channel number was considered as an optional equipment capability which allowed to pilot to use a 5-digit number to select a specific approach instead of using the menu method as we usually do to choose from our navigation database. These numbers correspond to only one type of approach and they’re unique.

Examples of approach charts WAAS (RNP Y 04L de KJFK) y EGNOS (RNP 06 de EHAM).

Below channel numbers, there is a combination of 4 letters and numbers. This is the approach identifier. In conventional radionavaids, when an ILS or VOR is selected, there is Morse code to aurally ident it. In this case, is visually identified to verify the selection and extraction of the correct approach chart from the navigation database. The first letter corresponds to augmentation system used: W for WAAS or E or EGNOS. The next two numbers are used for runway designator. When there are parallel runways, lest say LEFT, CENTER or RIGHT, letter A, B or C are added at the end. So, in KJFK, for the approach RNAV (GPS) Y 04L, our approach ident will be W04A.

2 thoughts on “THE WAAS CHANNEL.”

  1. What happens if the WAAS channel and the approach you’ve loaded from the database on the FMS are different? What does that mean / do?
    You can email me the answer/explanation, if yo have one, to: shannonjhall@gmail.com

    Thanks!

    1. Thank you Shannon. Let’s see I answer it correctly

      The FMSs usually, depending on the BDD supplier, use different codes to store the different approaches. The WAAS channel was used for GPSs (General aviation use most of them) of airplanes which don’t have FMS. But in the case your aircraft have both (GPS and FMS), I think there should be any inconsistency in some point of their databases and pilot should act in consecuence. Dates of databases and notams have to be considered as well.

      We have to take into consideration every time we load an approach we have to check WPt’s, tracks and altitudes passings before we shoot it.

      I hope it answers your question.

      Kindest regards.

Leave a Reply to Shannon Hall Cancel reply

Your email address will not be published.