Strange DME dropout with KNS 80

[haymak3r]

Hopefully this is the right location for this. But wanted to share an experience I had last week. While doing an instrument dual flight lesson with my instructor last week, we filed and departed KEUG bound for KRBG following the v448 airway and planned to fly the vor-a approach in to rwy 34 at KRBG. I planned to keep the EUG vor on the kns80(nav1) until we were 35nm away which was where v448 turned towards RBG at the ACONI waypoint. I had RBG freq selected on nav2. Once we made it there, I switched over to RBG freq on nav1. we listened for the RBG morse code, and heard it, and the cdi deflected correctly and I turned to follow it. DME appeared normal for about 30 seconds, and then all of a sudden we lost DME.

We knew the distance between ACONI and RBG, so I started slowing down and timed our approach to RBG. we were about 10 seconds off before the CDI flipped.  I then slowed to around 120, and per the approach plate we had to do a procedure turn back inbound within 10nm, so waited 3 minutes and initiated it. (not my best turn by far lol). Anyways, we turned inbound, saw the runway, canceled IFR, and then did a missed approach and continued back to KEUG. On climb out we checked for the morse code again, and still heard it. CDI deflected correctly as best we could see, but no DME the whole time. I switched back to EUG about 2 nm from KRBG, and was able to instantly pick up DME to EUG. So I don't think there is a problem with my kns 80 or anything?? I did try RBG again, and DME never showed up.

I checked notams and saw nothing. I checked the AFD, and double-checked that we weren't in a blind spot as we've flown here before without issue. We flew at 5000 ft and on a heading of 163 and then 157 following the approach plate. Turned to 202 and then around to 022 and back inbound on 337. All at 5000 ft. We never picked up DME at any time.

So do we pawn this off as a VOR/DME issue at the station? Is there anything you would do differently? This was an IFR lesson, and we were technically in VFR conditions for the most part. If you were in actual IMC, would you have diverted, or continued?

Cheers!

[ArtVandelay]

Make sure it’s getting a good supply of cooling air.

[haymak3r]

Hmmm, I suppose it could be dirty.. I can pull it and check when able. 

[ArtVandelay]

Hmmm, I suppose it could be dirty.. I can pull it and check when able. 

Mine had a cooling fan under the panel and a hose running to the back to give it cool air. Make sure the fan is working.

[LANCECASPER]

54 minutes ago, ArtVandelay said:

Mine had a cooling fan under the panel and a hose running to the back to give it cool air. Make sure the fan is working.

Exactly. Plus the hoses wear out or fall over the years and you don't realize it until you have a radio overheat.

[Wildhorsetrail]

Could the DME hold button be causing problems?

Sent from my SM-A326U1 using Tapatalk

[47U]

8 hours ago, haymak3r said:

we listened for the RBG morse code, and heard it, and the cdi deflected correctly and I turned to follow it. DME appeared normal for about 30 seconds, and then all of a sudden we lost DME.

Apology for my ignorance… does the KNS 80 allow you to listen to both the VOR Morse code identifier AND the DME Morse code identifier?  Is the DME identifier signal wired into your audio panel to select listen to the DME identifier?  

I only ask because the audio-out on my DME 890 wasn’t hooked up to the audio panel by the previous owner and he flew it that way for about 25 years.  The DME identifier also has a much longer interval between broadcasts than the VOR, like 30 seconds, I think.  

Good luck with your IFR training!

[haymak3r]

Interesting. I will look in to this. I have only ever checked the morse code for the VOR Identifier! I have always thought they were one in the same? Is there any distinction between the two? 

Thanks,
Chris

*EDIT - I did a quick google search on this. Interesting. I don't remember that from my PPL training lol. So it will transmit the same morse code but at a different slightly higher frequency as the VOR. So the beeps will be slightly faster. I'll have to listen for this at my home airport now. How interesting!!

Edited June 7, 2022 by haymak3r

[haymak3r]

15 hours ago, Wildhorsetrail said:

Could the DME hold button be causing problems?

Sent from my SM-A326U1 using Tapatalk
 

Not sure it would be, as when I switched back to EUG VOR, DME came back just fine.

[carusoam]

13 hours ago, haymak3r said:

Interesting. I will look in to this. I have only ever checked the morse code for the VOR Identifier! I have always thought they were one in the same? Is there any distinction between the two? 

Thanks,
Chris

*EDIT - I did a quick google search on this. Interesting. I don't remember that from my PPL training lol. So it will transmit the same morse code but at a different slightly higher frequency as the VOR. So the beeps will be slightly faster. I'll have to listen for this at my home airport now. How interesting!!

look this up… you may see it on the test… 
 

See if this sounds familiar…  it’s been too long since I used DME… GPS has legally made DME less useful….

The VOR has four spaces for Morse code….

When you receive only the VOR, you hear three codes repeated… and a space…

If you get four codes, the fourth one indicates the paired device is also broadcasting…

Fuzzy memory… can’t remember if the paired device is DME or ILS…

Either way… there must be a way to know the DME signal is the right one…(?)

Some radios make it easier than others… dialing in the VOR, dials in the DME at the same time… not two completely separate radios….

The KNS 80 was a really advanced navigator prior to GPS coming along…

Let’s invite @Jerry 5TJ he may know these kind of details…   

Let us know what you find out…

Best regards,

-a-

[Jerry 5TJ]

18 hours ago, haymak3r said:

So it will transmit the same morse code but at a different slightly higher frequency as the VOR. So the beeps will be slightly faster

The pitch of the Morse from the DME ident is higher, not the rate at which the letters are sent.  
The ident for the DME is transmitted on the DME frequency and you need to hear that audio from the DME receiver and not the separate audio ident from the VOR receiver.  
As 47U notes, the audio output from the DME receiver in the KNS80 must be connected to the audio panel if you are to hear the DME identifier letters.  
So — On your audio panel select DME, not NAV 1 or 2, and listen patiently.  DME ident are sent out only once every 30 seconds.  
My hunch is that the RBG site had a problem with its DME transponder equipment and shut itself down.   Another possibility is that the site was rate-limited: The ground-based DME transponder can only work with a limited number of aircraft at once. If too many aircraft attempt to interrogate the DME site simultaneously the ground equipment will ignore some of the planes’ interrogations.
DME use may be in decline in GA but many larger aircraft use DME/DME area navigation so they are equipped with multiple DME interrogators. 
 

[carusoam]

Way to go Jerry!

Today’s Classic Avionics Knowledge Award Winner!

Thanks for sharing the awesome details.

Best regards,

-a-

[haymak3r]

Thanks guys! Flew yesterday and performed some VOR DME Arc approaches to KCVO and KEUG. All worked just fine. I did not have a chance to listen to the morse codes outside of the normal checking if we get a code. I wanted to do it on the ground, but we were a little short on time for the lesson. I'll try to spend some time on my own to check on all of this.

[haymak3r]

7 minutes ago, carusoam said:

Way to go Jerry!

Today’s Classic Avionics Knowledge Award Winner!

Thanks for sharing the awesome details.

Best regards,

-a-

HA Classic.. You calling my bird old??!  

Just kidding of course. 

[Jerry 5TJ]

45 minutes ago, haymak3r said:

HA Classic.. You calling my bird old??!  

Just kidding of course. 

I think he was saying my knowledge is classic.  But, I prefer the term “seasoned professional” rather than  “old fart.”