Remove an Older DME?

B

Bluesky

Filing Flight Plan
Joined
Mar 17, 2025
Messages
4
Display Name
Bluesky123
I have not used my DME for years and I do not fly IFR any longer is it worth keeping or remove it?
 
Personally, if it works, I'd keep it. I still use mine once in a blue moon, and I like having it in case of a GPS outage. There's a lot of ILS approaches that require GPS or DME. Now in an emergency, I suppose ATC can give you distances, but I like having the box; it doesn't take up much space. If it's not in the way and it works, I see no reason to ditch it. As for resale value, only a small subset of crazy people like me would consider it a positive, but I don't think anyone would really consider it a negative.
 
Jim K said:
Personally, if it works, I'd keep it. I still use mine once in a blue moon, and I like having it in case of a GPS outage. There's a lot of ILS approaches that require GPS or DME. Now in an emergency, I suppose ATC can give you distances, but I like having the box; it doesn't take up much space. If it's not in the way and it works, I see no reason to ditch it. As for resale value, only a small subset of crazy people like me would consider it a positive, but I don't think anyone would really consider it a negative.
Click to expand...
Thank-you for your input. You made some good points and going to keep it.
Lawson_Stone said:
How much useful load would be gained by ditching the DME?
Lawson_Stone said:
How much useful load would be gained by ditching the DME?
Click to expand...
Not much ! I need to focus on my diet to gain some useful load LOL ! THX
Click to expand...
 
I too have an old DME that still works. I use it on almost every flight and intend to keep it. If it fails I'm not sure I would replace it, but it would be tempting since a used unit of the same make & model can be found for less than $500 these days.
 
There are a not-insignificant number of VOR-DME sites where the VOR has been shut down, but the DME is still shown as operational. e.g. HON, GCO (maybe cheaper for the FAA to maintain?) Seems like a DME could be useful, as Martin says, when GPS is down. [That said, I've never had the opportunity to use one.]
 
40YearDream said:
There are a not-insignificant number of VOR-DME sites where the VOR has been shut down, but the DME is still shown as operational., as Martin says, when GPS is down. [That said, I've never had the opportunity to use one.]
Click to expand...
That's correct, though those DMEs (without a VOR) are not all that useful to us light-GA pilots with the traditional old DME radios. They are very useful for FMS-equipped aircraft where the FMS can query multiple DMEs simultaneously and determine a position that way, and that's why the DME function is often retained even when the VOR is decommissioned. Distance measuring is more accurate than determining which VOR radial one is on, but it requires some math to turn those distances into a position (whereas radial-and-distance is pretty intuitive to understand).

- Martin
 
I removed mine as part of my panel upgrade. Haven't missed it, even when GPS was jammed over Myanmar.
 
Martin Pauly said:
That's correct, though those DMEs (without a VOR) are not all that useful to us light-GA pilots with the traditional old DME radios. They are very useful for FMS-equipped aircraft where the FMS can query multiple DMEs simultaneously and determine a position that way, and that's why the DME function is often retained even when the VOR is decommissioned. Distance measuring is more accurate than determining which VOR radial one is on, but it requires some math to turn those distances into a position (whereas radial-and-distance is pretty intuitive to understand).

- Martin
Click to expand...
And I am hoping that someone will get smart and add a box to our systems that gives us (GA) DME/DME/DME nav capability
 
Regulatory IFR question: If you don't have a DME but you do have a certified WaaS GPS having the DME locations in its database, the GPS can simulate the DME distance - even the slant distance since the GPS also knows your altitude. Does this mean that GPS serves as equivalent to a DME under normal conditions?

By "normal conditions" I mean things like, a GPS outage won't affect a true DME, ignoring those sorts of scenarios.
 
MRC01 said:
If you don't have a DME but you do have a certified WaaS GPS having the DME locations in its database, the GPS can simulate the DME distance - even the slant distance since the GPS also knows your altitude. Does this mean that GPS serves as equivalent to a DME under normal conditions?
Click to expand...
Yes. That’s pretty clearly outlined in AIM section 1-2-3. You don’t even need WAAS for that; a regular GPS without SBAS will do. No need for slant range, either - GPS shows a ground-based distance, but that’s OK.

The exception is you cannot use GPS in lieu of DME for lateral guidance on the final segment of an instrument approach. There’s this one weird approach at Martin State Airport with a curved final segment, defined by DME, and you can’t legally fly that with just GPS:


Regards,
Martin
 
Martin Pauly said:
The exception is you cannot use GPS in lieu of DME for lateral guidance on the final segment of an instrument approach. There’s this one weird approach at Martin State Airport with a curved final segment, defined by DME, and you can’t legally fly that with just GPS:
Click to expand...
I recently finished my instrument training at KMTN. We never flew that approach, but we did explore the plate in the context of DME arcs in general. That exception for lateral guidance didn't stick with me, so thanks for the reminder. I had to look it up: AC 90-108 8.b.
 
Interesting approach, so the MAP is on the DME arc. GPS can be used to do a DME arc so it would seem a GPS only could do this approach. Although looking closer, the MAP is BAL R-060 so I assume there is no fix in the GPS database...
 
Last edited:
Some people want to remove DMEs from their planes. Here I am, thinking about installing one in a plane that never had it.

Also thinking about building a box that auto-tunes it to get ranges and figure out positions. A nice example of real-life Kalman filtering.
 
AV8R_87 said:
Some people want to remove DMEs from their planes. Here I am, thinking about installing one in a plane that never had it.

Also thinking about building a box that auto-tunes it to get ranges and figure out positions. A nice example of real-life Kalman filtering.
Click to expand...

one challenge would be to ident the station. iirc, the dme transponders only transmit the morse code id once every 40 seconds.
 
Bob Noel said:
one challenge would be to ident the station. iirc, the dme transponders only transmit the morse code id once every 40 seconds.
Click to expand...
Worse yet, after tuning in a DME, it can take a while for your radio to figure out with of the ground station's responses are for your aircraft, because multiple aircraft share one DME. DME is not something you can switch every couple of seconds; thus DME-DME navigation in jets (controlled by an FMS) works with multiple DME channels in parallel.

- Martin
 
Martin Pauly said:
Worse yet, after tuning in a DME, it can take a while for your radio to figure out with of the ground station's responses are for your aircraft, because multiple aircraft share one DME. DME is not something you can switch every couple of seconds; thus DME-DME navigation in jets (controlled by an FMS) works with multiple DME channels in parallel.

- Martin
Click to expand...

it's interesting that overlapping responses will still allow the aircraft's DME to determine a range. Note that the interrogation rate is, crap, I don't remember, but it's something between 16 times per second to as much as 30 times per second... maybe more. I'm too laze to look it up.
 
Pinecone said:
And I am hoping that someone will get smart and add a box to our systems that gives us (GA) DME/DME/DME nav capability
Click to expand...

They have had this for a long time. It was a King rnav box that used DME. It was in a DC-3 I flew in early 80's. It was a KNS 80 I believe. The omega/vlf system I had in a DC-4 did the same.

Most all current FMC's in current airliners, can use dme to help in case of gps outages.
 
Bob Noel said:
one challenge would be to ident the station. iirc, the dme transponders only transmit the morse code id once every 40 seconds.
Click to expand...
You scan, establish range and validate the station only after the ID comes through. That can be a couple scan cycles later.

Martin Pauly said:
DME is not something you can switch every couple of seconds; thus DME-DME navigation in jets (controlled by an FMS) works with multiple DME channels in parallel.
Click to expand...
A DME can go from aquisition to tracking in 10 seconds or less. I had a single, 3-channel DME that had ch1 assigned to the copilot, ch2 assigned to the pilot and ch3 assigned to the FMS - the FMS had no trouble figuring out a decent position with just one DME channel.
 
turbosuper said:
Interesting approach, so the MAP is on the DME arc. GPS can be used to do a DME arc so it would seem a GPS only could do this approach.
Click to expand...
GPS can only be used in lieu of DME when it's not being used for lateral guidance on the final approach course. The arc at MTN is the final. It's the one remaining case where GPS cannot substitute for DME.
 
Albany Tom said:
I read the title as "remove an older DPE", and thought "well that sounds pretty harsh! I need to warn some people."
Click to expand...
So, when the check ride isn't going your way, instead of getting a continuation............
 
Martin Pauly said:
Yes. That’s pretty clearly outlined in AIM section 1-2-3. You don’t even need WAAS for that; a regular GPS without SBAS will do. No need for slant range, either - GPS shows a ground-based distance, but that’s OK.

The exception is you cannot use GPS in lieu of DME for lateral guidance on the final segment of an instrument approach. There’s this one weird approach at Martin State Airport with a curved final segment, defined by DME, and you can’t legally fly that with just GPS:


Regards,
Martin
Click to expand...
Fun approach. I flew it as a TACAN approach when I was flying the A-10 out of KMTN.
 
You must log in or register to reply here.
Back
Top