Value of DME

[Jamie Kirk]

I can’t remember the last time there was a vor at my destination

Picked up new plane in Michigan and got all the way to new Mexico before we realized the previous owner only had East Coast maps loaded. Flew the entire way home to Southern California off DMEs and VORs

 

[Skyrys62]

I agree with @Bill Jennings.

You probably have your phone as a GPS backup at a minimum, If not ipad /something else. Plus could you not contact a center to get some sort of radar vectoring in a dire situation?

 

[steingar]

I agree with @Bill Jennings.

You probably have your phone as a GPS backup at a minimum, If not ipad /something else. Plus could you not contact a center to get some sort of radar vectoring in a dire situation?

With my VOR/DME combination loosing the GPS isn't a "dire situation". May not be a VOR approach where I'm going, but I bet there'll be one (or an ILS) somewhere nearby. But yeah, if all else fails there's the iPad.

 

[Skyrys62]

With my VOR/DME combination loosing the GPS isn't a "dire situation". May not be a VOR approach where I'm going, but I bet there'll be one (or an ILS) somewhere nearby. But yeah, if all else fails there's the iPad.

I meant a dire situation as in you do not have your DME, then GPS systems fail, would there still be the option of radar vectoring from ATC/ACC?

Although, I'm sure they would be very busy during a sudden GPS outage lol.

 

[flyingron]

I put the DME in my plane back in 1995 or so because I was based at IAD where the class B rings were predicated on DME (didn't have a GPS back then) and a few of the ILS approaches into there required DME as well. As stated, losing the GPS these days still leaves me with the #2 VOR/LOC/ILS and it's not that hard finding an approach *somewhere* that doesn't need a DME. Besides, in an emergency and if you have coms, ATC can help

 

[jsstevens]

I have a KLN94 in my panel. My plan is to use alternates that have ILS.

I am aware. That's why I mentioned it. For a 90's computer box I thought the interface was quite good. The manual was top notch.

 

[n2230b]

We are at a CROSSROADS.......

Like Robert Duval said in one of his Westerns:

From the sweet grass to the packing house,
From the cradle to the grave......
We are travelers between two eternities

 

[steingar]

I am aware. That's why I mentioned it. For a 90's computer box I thought the interface was quite good. The manual was top notch.

I thought it was a lot of bang for the buck, and the new Garmin boxes handn't come out yet.

 

[George Mohr]

Imagine you lose your GPS in IMC and have to revert to VOR navigation. Think you'd appreciate a working DME then? I would.

 

[SCCutler]

If I had a working DME in my plane, no way I’d take it out. Too useful, simple and (importantly) not subject to jamming.

 

[asicer]

Imagine you lose your GPS in IMC and have to revert to VOR navigation. Think you'd appreciate a working DME then? I would.

I wouldn't appreciate a working DME during a GPS outage. The planes in the rental fleet available to me either had GPS or were /U so I got comfortable with dual VOR navigation and never really worked with a DME.

 

[steingar]

Had I two VORs the DME would be superfluous. I don't, so I like my DME. Like I said, I'll fix it if it breaks.

 

[George Mohr]

I wouldn't appreciate a working DME during a GPS outage. The planes in the rental fleet available to me either had GPS or were /U so I got comfortable with dual VOR navigation and never really worked with a DME.

That's a great place to be. Seems to me that many GA pilots aren't super proficient on VOR approaches these days, and in particular using two nav heads for fixes. I can speak for myself there...

 

[AA5Bman]

Reviving this thread as I am in the same boat as OP - keep a working DME or toss it during a panel upgrade (to GTN650/G5). I don’t have panel space issues or need the cash, necessarily, so keeping it would be fine, but I’m kinda in the less-is-more camp, and I don’t want to have to remove or fix it later.

That said, it still works just fine. The thing I’m unsure about is whether or not getting rid of the DME will reduce (in a meaningful way) the number of approaches I can fly. I’m new to the IFR GPS game (believe it or not, I got and have flown IFR entirely with old round gauges), so I’m a little unsure about this. If DME is listed on an approach, is the GPS an allowable substitute or do you have to actually have the DME?

As an example, here’s a fun one, could you fly this arc without a DME installed in your plane if you have an IFR GPS?

https://flightaware.com/resources/airport/KOTH/IAP/ILS+OR+LOC+RWY+04

 

[Palmpilot]

Reviving this thread as I am in the same boat as OP - keep a working DME or toss it during a panel upgrade (to GTN650/G5). I don’t have panel space issues or need the cash, necessarily, so keeping it would be fine, but I’m kinda in the less-is-more camp, and I don’t want to have to remove or fix it later.

That said, it still works just fine. The thing I’m unsure about is whether or not getting rid of the DME will reduce (in a meaningful way) the number of approaches I can fly. I’m new to the IFR GPS game (believe it or not, I got and have flown IFR entirely with old round gauges), so I’m a little unsure about this. If DME is listed on an approach, is the GPS an allowable substitute or do you have to actually have the DME?

As an example, here’s a fun one, could you fly this arc without a DME installed in your plane if you have an IFR GPS?

https://flightaware.com/resources/airport/KOTH/IAP/ILS+OR+LOC+RWY+04

Yes, you can use an IFR GPS to fly DME arcs like that, because the DME is not providing lateral guidance on the final approach course.

If I had a working DME, I would keep it, because of the military's recurring GPS-interference testing.

 

[Doug Reid]

Like Palmpilot, I would keep DME if it is installed.

 

[AA5Bman]

Yes, you can use an IFR GPS to fly DME arcs like that, because the DME is not providing lateral guidance on the final approach course.

If I had a working DME, I would keep it, because of the military's recurring military GPS-interference testing.

Maybe you can help me out, because I am really struggling to understand when it is okay to substitute an IFR GPS for the ground-based navigational equipment of an approach. Is the rule that you can navigate the whole approach up to the final approach fix, and then that final segment has to be on the designated navigational aid? Like, for instance, you can fly an ILS to the point of the final approach fix with your GPS as the primary navigational equipment, but from that point on you have to navigate with your Localizer/GS?

In the approach I pasted in, it actually lists "ADF AND DME REQUIRED". Since it's actually an ILS, is that entirely untrue - neither ADF nor DME is required provided you have an IFR GPS? It looks like the holding fix is the LOM (ADF). Do you have to have an ADF to identify that fix, or could you do it with the GPS?

 

[Palmpilot]

According to the AIM, an IFR GPS is a valid substitute for ADF and DME except as lateral guidance on the final approach course. (I don't have the section number at the moment.) I'm not sure exactly where on the final approach course you have to start using the ground-based navaid for lateral guidance.

I suppose they could word the note as "ADF AND DME, OR A SUITABLE RNAV SYSTEM REQUIRED," but that would be a lot of a verbiage.

 

[PPC1052]

Is the rule that you can navigate the whole approach up to the final approach fix, and then that final segment has to be on the designated navigational aid? Like, for instance, you can fly an ILS to the point of the final approach fix with your GPS as the primary navigational equipment, but from that point on you have to navigate with your Localizer/GS?

Yes.

In the approach I pasted in, it actually lists "ADF AND DME REQUIRED". Since it's actually an ILS, is that entirely untrue - neither ADF nor DME is required provided you have an IFR GPS? It looks like the holding fix is the LOM (ADF). Do you have to have an ADF to identify that fix, or could you do it with the GPS?

The ADF is only required for the missed (or, if EMIRE is your IAF of choice, to identify the IAF). So you are good to go to fly this with a WAAS GPS.

 

[AA5Bman]

The ADF is only required for the missed (or, if EMIRE is your IAF of choice, to identify the IAF). So you are good to go to fly this with a WAAS GPS.

Just to clarify, it's actually more like you're able to navigate this approach with your WAAS GPS to the final approach fix but you have to fly the final segment on your Loc/GS, right? Also, the reason you can use the GPS to identify the NDB holding fix is the same - it's not "providing lateral guidance on the final approach course."

Is there ever a circumstance where DME provides lateral guidance on a final approach segment? I can't think of how that would work.

I think I went off the rails thinking about the old GPS overlays. Do those exist anymore? Is my understanding correct that you can fly an entire "overlay" approach with an IFR GPS, including the final approach segment? Of course, in that case I think the title of the approach has to be ADF OR GPS or VOR OR GPS, in which case it can really just be thought of as a GPS approach.

 

[Palmpilot]

I found the AIM section. It's 1-2-3 (in the August 2019 edition).

 

[Caramon13]

I mean you can find an exception to any rule in most cases, however, I stand by my original comment. Why keep an old, heavy outdated piece of equipment in your plane for the 1 or two situations when you may need it ever, when you can free up panel space for something more useful and use GPS in lieu of it.

If you have a DME and a GPS in your plane, what does your eye go to first when you are looking at distance remaining to a point? Or if you want to quickly see nearby airports. You probably aren't tuning in the DME to those, you just eyeball the GPS and go. GPS is better than good enough..lose the DME.

@AA5Bman DME is not lateral guidance.

 

[Palmpilot]

I mean you can find an exception to any rule in most cases, however, I stand by my original comment. Why keep an old, heavy outdated piece of equipment in your plane for the 1 or two situations when you may need it ever, when you can free up panel space for something more useful and use GPS in lieu of it.

If you have a DME and a GPS in your plane, what does your eye go to first when you are looking at distance remaining to a point? Or if you want to quickly see nearby airports. You probably aren't tuning in the DME to those, you just eyeball the GPS and go. GPS is better than good enough..lose the DME.

@AA5Bman DME is not lateral guidance.

"Different strokes for different folks." There are a lot of factors that might go into any individual's decision. One factor might be how often you see GPS-interference-testing NOTAMs affecting your area. They seem to come out about once a month or so here in the SW U.S.

As for a DME-ARC final approach course, I think I have heard that there are few, but they are very rare.

 

[PPC1052]

Just to clarify, it's actually more like you're able to navigate this approach with your WAAS GPS to the final approach fix but you have to fly the final segment on your Loc/GS, right?

Yes. Exactly. Sorry about the imprecision in my prior post.

 

[Caramon13]

"Different strokes for different folks." There are a lot of factors that might go into any individual's decision. One factor might be how often you see GPS-interference-testing NOTAMs affecting your area. They seem to come out about once a month or so here in the SW U.S.

As for a DME-ARC final approach course, I think I have heard that there are few, but they are very rare.

Fond Du lac has a DME arc for the IAF and DME is required for it. So yeah, if you fly that one approach at that ONE airport, maybe you can justify DME. KFLD has 4 other approaches too btw..two of which are RNAV.

 

[asicer]

Fond Du lac has a DME arc for the IAF and DME is required for it. So yeah, if you fly that one approach at that ONE airport, maybe you can justify DME. KFLD has 4 other approaches too btw..two of which are RNAV.

View attachment 81084

Maybe I haven't had enough coffee this morning, but where on that chart does it say that you cannot use GPS distance as DME?

The FAF is at BAGOE so the arc doesn't count as a final approach course.

 

[Palmpilot]

Fond Du lac has a DME arc for the IAF and DME is required for it. So yeah, if you fly that one approach at that ONE airport, maybe you can justify DME. KFLD has 4 other approaches too btw..two of which are RNAV.

View attachment 81084

That DME arc is not part of the final approach course. The question was whether there are any approaches where a DME arc takes you all the way to the runway.

 

[Caramon13]

Yep sorry put the wrong one there, here you go:

 

[Martin Pauly]

One different consideration is if you want to fly IFR internationally or are thinking of the aircraft's resale value (read: international buyers), a DME is still legally required for IFR in many places around the world.

- Martin

 

[flyingcheesehead]

Here's the exception that's always talked about. The KMTN VOR/DME or TACAN Z RWY 15 has a DME arc final approach course (the link is to the PDF which is easier to read):

This is more of an Internet curiosity than anything else, since there's also an RNAV approach to the same runway that has lower minimums. I'm not sure why this approach even exists any more.

Is there ever a circumstance where DME provides lateral guidance on a final approach segment? I can't think of how that would work.

Yes, but it's very rare. There's the one above, and I think one other one though I forget where that is.

@AA5Bman DME is not lateral guidance.

It is when you're on a DME arc. It's very rare for a DME arc to be part of the final approach segment, though it obviously does happen.

Fond Du lac has a DME arc for the IAF and DME is required for it. So yeah, if you fly that one approach at that ONE airport, maybe you can justify DME. KFLD has 4 other approaches too btw..two of which are RNAV.

That arc is not part of the final approach segment, so you can use GPS for it.

That DME arc is not part of the final approach course. The question was whether there are any approaches where a DME arc takes you all the way to the runway.

Yes, there are, shown above. But again, not much more than an Internet curiosity at this point. IMO, there is no compelling reason to have a DME. If you want to leave it in as a backup, fine - But think ahead to what you might do if it fails. Would you pay money to repair/replace it at that point?

 

[Caramon13]

Here's the exception that's always talked about. The KMTN VOR/DME or TACAN Z RWY 15 has a DME arc final approach course (the link is to the PDF which is easier to read):

It is when you're on a DME arc. It's very rare for a DME arc to be part of the final approach segment, though it obviously does happen.
?

Incorrect, DME provides NO lateral guidance. It's a distance. Lateral guidance is provided by ILS/LOC/LPV LNAV/VNAV approaches.

The arc is just a distance. On a LOC or ILS approach you can see how far off you are from a point based on the deflection of the needle. A DME says "20", that offers no guidance, it's just a number.

If you are too far right the needle is deflected. A DME cares not how far you are off course and offers you NO guidance to get back on course. It just says 20.

 

[flyingcheesehead]

Incorrect, DME provides NO lateral guidance. It's a distance. Lateral guidance is provided by ILS/LOC/LPV LNAV/VNAV approaches.

The arc is just a distance. On a LOC or ILS approach you can see how far off you are from a point based on the deflection of the needle. A DME says "20", that offers no guidance, it's just a number.

Look at that approach again. The DME is providing the lateral guidance on the final approach course, because the final approach course is a DME arc. The VOR, on that approach, is providing the distance information.

Put another way: The final approach course is the 14.7 DME arc. It's not "just a number" - If your DME says 16, you're left of course, if the DME says 13, you're right of course. Left. Right. Lateral guidance. The VOR is telling you how far you are from the runway: The MAP is at the 060 radial, not a DME distance, because the DME distance should be remaining roughly the same throughout the approach.

Put yet another way: You don't need a needle or a magenta line to provide course guidance. You sometimes need your brain. Think about an ADF approach - The needle doesn't actually tell you whether you're on course on an ADF approach, just like how the number doesn't directly tell you whether you're left or right of course on this approach. You need to use your brain to interpret that information. That's why VOR approaches are better than NDB approaches - It's being fed to you rather than making you think about it. Lower workload. Safer.

 

[Caramon13]

Look at that approach again. The DME is providing the lateral guidance on the final approach course, because the final approach course is a DME arc. The VOR, on that approach, is providing the distance information.

Put another way: The final approach course is the 14.7 DME arc. It's not "just a number" - If your DME says 16, you're left of course, if the DME says 13, you're right of course. Left. Right. Lateral guidance. The VOR is telling you how far you are from the runway: The MAP is at the 060 radial, not a DME distance, because the DME distance should be remaining roughly the same throughout the approach.

Put yet another way: You don't need a needle or a magenta line to provide course guidance. You sometimes need your brain. Think about an ADF approach - The needle doesn't actually tell you whether you're on course on an ADF approach, just like how the number doesn't directly tell you whether you're left or right of course on this approach. You need to use your brain to interpret that information. That's why VOR approaches are better than NDB approaches - It's being fed to you rather than making you think about it. Lower workload. Safer.

A number isn't guidance. Does a COM radio provide lateral guidance when you are on frequency 120.1 instead of 120.05? I agree that it is important to maintain the proper distance and yeah you can infer a turn left or right will get you back on course, but there's no guidance being provided by DME. It says 20, then it says 19. It tells you nothing about the magnitude of your deviation relative to a desired course, unlike LOC or ILS which have dots and a needle indicate where you are, the magnitude you are off and more importantly, how to guide you back to centerline for a proper approach.

If the DME says 13, does it show you if you should turn left or right to get back on course? Nope.

Guidance - the directing of the motion or position of something. 20 doesn't tell you anything. It tells you 20. There is no guidance to get you back to 21 or to tell you if where you are is REALLY far off relative to where you SHOULD be on that approach. The FAA provides some guidance (see what I did there) for flying an arc, but the DME does not.

To illustrate this if you see this in the soup: (20) without using anything else, what guidance does it give you to get back to 26?

 

[flyingcheesehead]

A number isn't guidance. Does a COM radio provide lateral guidance when you are on frequency 120.1 instead of 120.05? I agree that it is important to maintain the proper distance and yeah you can infer a turn left or right will get you back on course, but there's no guidance being provided by DME. It says 20, then it says 19. It tells you nothing about the magnitude of your deviation relative to a desired course, unlike LOC or ILS which have dots and a needle indicate where you are, the magnitude you are off and more importantly, how to guide you back to centerline for a proper approach.

If the DME says 13, does it show you if you should turn left or right to get back on course? Nope.

Combined with the plate, it does.

To illustrate this if you see this in the soup: (20) without using anything else, what guidance does it give you to get back to 26?

Never said "without using anything else". It's the same thing with NDB approaches. The needle points to 178. What does that tell you, if you don't look at the plate and *interpret* what the needle is telling you? However, you are still using your ADF for lateral guidance.

I'll try one more time: On the MTN approach linked above, what tells you whether to turn left or right when you're past the FAF?

Spoiler alert: It's the DME. Thus, the DME is providing your lateral guidance on the final approach course and you cannot use GPS to substitute for it in this case.

 

[Caramon13]

Combined with the plate, it does.

Never said "without using anything else". It's the same thing with NDB approaches. The needle points to 178. What does that tell you, if you don't look at the plate and *interpret* what the needle is telling you? However, you are still using your ADF for lateral guidance.

I'll try one more time: On the MTN approach linked above, what tells you whether to turn left or right when you're past the FAF?

Spoiler alert: It's the DME. Thus, the DME is providing your lateral guidance on the final approach course and you cannot use GPS to substitute for it in this case.

The SLOAF waypoint is identified by the lateral guidance of the VOR and the distance from the DME, you fly the DME arc based on the distance from the VOR. The radials are from the VOR, THEY provide lateral guidance.

Show me where on the DME it says turn left. Or right. Or anything that provides lateral guidance of any sort. It's a number. There is no guidance. What if you turned left at SLOAF, DME is still going to show 26 if you are on a left arc, there's nothing to show you on the DME that you should have turned right instead.

An ADF shows you where to go, it's a big gauge with an ARROW. A DME does NOT show you where to go. Not sure why this is so hard. You are looking at a map and you see 26, your DME says 20. Doesn't show you how to get to 26. You are using the MAP for guidance.

DME determines how far away you are from a point. If you are left or right of that point, but the same distance, it doesn't care does it? Similar, VOR's are lateral, not distance. If you tune in a VOR you won't know how far you are from it, but you'll know which way to turn to get to it.

Turning left or right to get a number higher or lower isn't lateral guidance.

 

[flyingron]

That DME arc is not part of the final approach course. The question was whether there are any approaches where a DME arc takes you all the way to the runway.

Two, there's one at Martin State (https://aeronav.faa.gov/d-tpp/1913/05222VDTZ15.PDF) and one at Wallops Island (https://aeronav.faa.gov/d-tpp/1913/00639VDT10.PDF). The latter is a NASA facility so you're unlikely to go there. I've been into MTN a bunch (used to be based at 1W2), but never flew that approach.

 

[dmspilot]

An ADF shows you where to go, it's a big gauge with an ARROW. A DME does NOT show you where to go. Not sure why this is so hard. You are looking at a map and you see 26, your DME says 20. Doesn't show you how to get to 26. You are using the MAP for guidance.

The FAA says RNAV may not be used as "substitution for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment."

NAVAIDs provide lateral guidance not cockpit displays. An ADF is not a NAVAID. NDB is a NAVAID. NDBs don't have "arrows telling you where to go."

The argument "ADF is lateral guidance because it has an arrow and DME doesn't have an arrow therefore a DME is not lateral guidance" might be truly the absolute dumbest thing I have ever read on this forum.

 

[Caramon13]

The FAA says RNAV may not be used as "substitution for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment."

NAVAIDs provide lateral guidance not cockpit displays. An ADF is not a NAVAID. NDB is a NAVAID. NDBs don't have "arrows telling you where to go."

The argument "ADF is lateral guidance because it has an arrow and DME doesn't have an arrow therefore a DME is not lateral guidance" might be truly the absolute dumbest thing I have ever read on this forum.

Way to take exactly what I wrote and completely miss the point. It doesn't matter how you argue it, DME does NOT provide lateral guidance. And for the purpose of this discussion we're not talking about NAVAIDS we're talking about equipment in a panel.

Maybe you should re-read the OP?

 

[dmspilot]

Way to take exactly what I wrote and completely miss the point. It doesn't matter how you argue it, DME does NOT provide lateral guidance. And for the purpose of this discussion we're not talking about NAVAIDS we're talking about equipment in a panel.

So what provides lateral guidance on a DME arc?

 

[Caramon13]

So what provides lateral guidance on a DME arc?

You do.

ON an arc, lets say the distance you have from the whatever is 26 nm. You get 6 NM of leeway on either side. So if the number is 20 or 32 in this case that's your "guidance" from the 26. Really 4 NM on either side, 2 is the secondary area. So YOU are providing your own. DME isn't providing it for you, it just tells you the number. If you deviate from that 26 you correct it. You provide your own lateral guidance. The equipment (and the NAVAID) have no concept of that 6 NM on either side.

Whereas if you are on a LOC Approach, LNAV, LPV the localizer is providing lateral navigation guidance. It's telling you you are left or right of course. You don't have to "do the math" and there is no fixed amount of deviation, it changes and gets more precise as you get closer.