Thoughts on DME?

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CA182R

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CA182R
While in the process of redoing the instrument panel towards a GPS WAAS airplane with ILS capabilities, I'm wondering if having a DME receiver brings much value (not financial value).

Not many manufacturers, pretty much only BK, and lots of old units around for sale.
 
I think it would depend heavily on how you intend to use the airplane. If you are planning on flying hard IMC and want maximum preparedness in case of GPS outage, and are installing other VHF based (VOR/LOC) navigation, an inexpensive KN64 or something might be worthwhile adding on. Otherwise, I wouldn't bother. GPS is legal for all things that DME would otherwise provide, so unless you want a complete belt and suspenders panel, it's just dead weight. In my personal plane I do keep a DME (KN62A) along with everything else for the just in case, but I also have a standby alternator, etc as I'm big on backup (though I do only have one engine!)
 
My plane has a kn62 in it. It's light and doesn't take up much space at all. I use it more than I expected. Nothing I couldn't live without, but it's usually tuned to the vor on my home field, so I know how far from home I am, even if the gps is set to another destination.

I also like the idea of having it and the kx155 to fly an ils if my gtn went TU, or I find myself in a GPS outage. I think there's still value in a dme, and like you said used ones are pretty cheap and easy to find these days.
 
I would not remove a DME if I had one in the panel. If or when there is a widespread GPS outage, it'll come in very handy.
On the other hand, for me this is an unlikely/rare enough thing that personally I won't go through the trouble of adding DME to my panel (which doesn't have it today).

- Martin
 
I kept mine when I added GPS, but I doubt I would have purchased and installed one had it not already been there.
 
The previous owner removed the old KN 64. Wish he hadn't... But not worth the 1000s to put another used one in. Still a bit sad, even if I would use it just for "sport". Just need to not think about it... Just another cost down the road when something breaks.

I just realized I do have a "DME" (advisory) backup for the GPS should it become unavailable, and if I have no other option including ATC instructions and ILS glideslope. The Aera 660 can do 3D positioning (15-20ft accuracy) with GLONASS satellites. Probably more accurate than the .1 NM on a KN.
 
I’m in the same panel upgrade process and went through the same questioning. Ultimately I decided that keeping the Aera 660 panel mounted to augment the GNC355 would be far more useful than keeping the KN64, and there is not enough room in the stack for everything so the DME has to go.

I like the idea of a full terrestrial setup, which is what I learned to fly instruments on, but the reality is that once the GPS is installed the DME likely will never be used. In the event of a GPS outage I can still fly an ILS and I am usually in a radar environment, so any practical lost functionality is minimal.
 
I would remove it. The display on those units have a given life and the replacement displays are becoming more difficult to obtain.
 
Clip4 said:
I would remove it. The display on those units have a given life and the replacement displays are becoming more difficult to obtain.
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Your heart has a limited lifetime too, so might as well remove it now. This advice makes no sense to me.
 
Absent other factors there's little to no value in keeping a DME in the panel if you're adding an IFR GPS. It does nothing the GPS can't do, and even in the event of a GPS receiver problem or regional outage a "backup" DME isn't a critically needed form of redundancy. If I was in your shoes, I'd eliminate it from the panel.

Plus, we've established you do not need an actual DME receiver to fly the MTN VOR or TACAN runway 15 approach, so just in case you were worried about that, don't be. ;)
 
If it were me, the deciding factor would be whether it still had resale value. If so, might as well cash in now before it's worthless. If resale value is already at or near zero then it's probably worth more staying in the panel, assuming it's still perfectly functional.
 
When I upgraded to the GNC355, I installed a DME.
I love it and glad I did.
Why?
GPS => Fancy New Hotness
KX-177b + KN64 DME => More solid than a soviet fighter

In the time since I installed the GPS, I've had NOTHING but trouble trying to get the Comm settings just right and ended up sending it back for warranty.
That KX177 takes a lickin' and keeps on tickin' and the DME is just the natural complement to it.

Install the damn DME. You'll be glad you did.
 
Salty said:
Your heart has a limited lifetime too, so might as well remove it now. This advice makes no sense to me.
Click to expand...

if you want to spend money to maintain a box you don’t use that’s on you. I’d clean up the panel and call it a day. You won’t find DME in late model airplanes.
 
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CA182R said:
Out of curiosity, how is this configured?

Thank you.
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https://bandc.com/product/cessna-210-standby-alternator-system-components-stc-pma/#installation-kit

It mounts to the vacuum pump pad and provides 20A of standby power. It’s a hot standby so automatically starts providing power if it senses the main alternator go offline. My airplane is all glass and LED, so can provide pretty much all my needs unless I was running all the lights and pitot heat, in which case I’d have to shed some load (a light flashes if you need to shed load). All my breakers a Klixon pullable ones, so that’d be easy to do if needed.
 
I kept my KN64 DME when I put in the WAAS GPS 15 years ago. I can tell you that I've not used it since. I've turned it on a few times for amusement purposes only.
 
I removed the DME from my bonanza when we had a major avionics upgrade. If gps really does go down, there will be much bigger issues than can be fixed by having a DME.
 
Groundpounder said:
I removed the DME from my bonanza when we had a major avionics upgrade. If gps really does go down, there will be much bigger issues than can be fixed by having a DME.
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My thinking was if my GPS receiver failed, not the entire constellation, I'd still be able to fly VOR and ILS approaches with DME.
 
Salty said:
My thinking was if my GPS receiver failed, not the entire constellation, I'd still be able to fly VOR and ILS approaches with DME.
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There are plenty of either kinds of approaches that can be flown without DME, and I have three independent GPS's in my airplane, not counting anything handheld, so I'm not too worried about redundancy. But, if you only have a single GPS, and already have a DME installed, I would not remove it
 
I plan to keep my King 64 DME for redundancy and I use it a lot when flying under Bravo air space. My GPS is tracking distance to the next waypoint and the DME is tracking Bravo rings.
 
I removed ours but I think I wish I'd kept it, it would display on our G500 TXi. We've lost GPS a couple times flying near the test areas in Utah, and while ATC would put you on a heading until you get it back (no big deal) it would have been neat to play with. In Mexico some of the approaches "require" DME and I think you're not supposed to use GPS, although I would and WAAS GPS is both more accurate and more reliable. Ironically GPS works better in Mexico because they don't intentionally block it to test cruise missles or whatever the military does up here.

In practice probably doesn't have much value but it's a neat to have if not a nice to have.
 
I have a GTN 750 and G500TXi. I kept my trusty KNS80 and can still use it for RNAV direct if there is a GPS outage. It was free backup because it was already installed. I can command my Stec 60-2 via the KNS80/G500TXi and fly a coupled ILS with it. I also kept my ST-901 GPSS that I can use to command my AP if the G500TXi goes dark, although I would need the GTN 750 working and could only fly RNAV (GPS) approaches with LNAV. I also have a G5 as a backup and a B&C standby alternator. If I lose all electrical, I will rely on my iPad and or Aera 796 and the G5.
 
My airplane came with one. Could give situational awareness in some situations. Fun toy to play with. No big hurry to remove it, and if it breaks I'll replace it if I can do so on the cheap.
 
Ed Haywood said:
When was the last time GPS went down?
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The U.S. military has published plans for domestic GPS interference testing several times a year. To what degree that disrupts civilian navigation, I don't know, because I'm not based in an area where the notams predict problems at the altitudes I fly.
 
Ed Haywood said:
When was the last time GPS went down?
Click to expand...

Probably more often than you think. Think about on a cross country if GPS goes down, how do you navigate and get down? With military jamming and if there is ever a real or perceived national threat the constellation is going down. I have lost GPS a couple of times, can be an interesting time if you are IMC or even in VMC in unfamiliar places.
 
My DME recently died. I am sad....but now I'm over it. Eventually I'll have it taken out to give me some useful load. My GNS530W and my GNC255A both give me "DME" now instead of the whatever brand I have in there. It has no name on the face.
 
If you are relying on the GPS for your ILS capability, then the DME won’t do much for you when the GPS goes belly up. If OTOH you have an independent NAV for ILS work, then it could be very helpful if you ever lose the GPS unit.,
 
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