NAV Ident Drop-out During TX

I know there has been a long-standing issue with the sensitivity of the VHF Nav receiver and the ability of the unit to decode the station identifier.  I also read that there is an improvement to this functionality in the next software release. What follows might be the same issue, or it might be something different.

I was out flying practice approaches the other day.  While flying the ILS at a towered airport, I noticed that the ILS identifier would flag each time I transmitted on the Comm radio to talk to Tower.  This naturally produces a CAS message for the pilot to check the navaid manually.

Of course, the identifier doesn't get decoded again until the radio "hears" the Morse code sequence correctly and completely at least twice in a row.  Which is right about the time I need to broadcast my new position again to Tower.  (Entering/exiting the procedure turn, crossing approach fixes.)

I understand that a VHF Com broadcast in close proximity (from the same radio, or even from the same airplane) can overload the VHF Nav receiver.  If I had been transmitting on my "other" radio, I wouldn't even be making this post.  But within the IFD itself, I see a potential solution.  Seems like there could be logic within the IFD to "hold" the VHF Nav station identifier data while the VHF Com is transmitting.  Then, when the broadcast ends, the IFD only needs to 'listen' to the Morse code once to see if it still matches the held value.

If the VHF Com signal is being broadcast from a non-IFD radio onboard the aircraft, then I would expect the current behavior.  I see the CDI flag on the other Nav receiver when a radio is transmitting, but the flag pulls away the moment transmission ends, and that radio doesn't have CAS messages.

David Bunin

Sure.  I can download the logs the next time I'm at the hangar.  The approach was the ILS 18 at KHQZ.  ILS frequency is 109.75 and the Tower frequency is 120.30.  I was flying the full procedure turn and they wanted my position entering the turn, existing the turn, passing PQF, and so on (it was a busy day and they're a non-radar tower).  I lost count of how many times I had to clear the CAS message during the approach.

Luckily (in terms of troubleshooting) or unfortunately (in operational terms) it seems pretty consistent on the ILS closest to my home airport.

Yes, I think you received a response from the Tech Support team yesterday.

My mistake, they said they had replied but it must have been someone else. In any case, you should be hearing from someone soon. It sounds like the com and nav coaxes are too close or they might need to be replaced.

Maybe reseat the box? Fixed one of my issues on a different radio (lazy bearing pointer).