Approach naming when DME is req'd

ArrowFlyer86

ArrowFlyer86

Pattern Altitude
PoA Supporter
Joined
Jul 17, 2019
Messages
1,933
Location
Chicago suburbs
Display Name
Display name:
The Little Arrow That Could
What's the difference between an approach named "LOC/DME" vs just "LOC" but with a requirement for DME in the specs? Is there any difference in the requirements?

Examples
Airport: KIMT
Approach name: "LOC/DME BC RWY 19"
With DME in the name...

upload_2023-1-12_14-8-10.png

...versus ...

Airport: KJMS
Approach name: "LOC BC RWY 13"
Requirement: DME

upload_2023-1-12_14-7-36.png


Is this just inconsistent approach naming convention, or is there another difference I'm not picking up on? At first I dismissed it but now I've seen it on a few charts and wondering if there is some difference.
 
midlifeflyer said:
Yeah, but why is the new one titled "LOC/DME" and the old one isn't?
Click to expand...

The IMT LOC/DME BC RWY 19 was last amended (to Amdt 13C) via NOTAM:

https://www.faa.gov/aero_docs/acifp/NDBR/6BDD7B314002416AB9C8EF22C19F658E-IMT-NDBR/P-NOTAM_MI_IMT_LDBC19_AMDT 13C.pdf

Name changes are not permitted via NOTAM (FAAO 8260.19I, Table 8-3-1).

Actually, 13A, 13B and 13C were all NOTAMs:

https://www.faa.gov/air_traffic/fli...9C8EF22C19F658E-IMT-NDBR&type=ndbr&nasrId=IMT

The last full amendment was Amdt 13 from way back in 2000.
 
midlifeflyer said:
Interesting... Chart design and nomenclature changes, ok on an abbreviated amendment. Approach name changes require a full amendment.
Click to expand...

It's actually a little more granular than that. This is getting into the weeds, but:

Full amendments require a full form 8260-3 or 8260-5. Anything and everything can be changed this way.
Abbreviated amendments can be promulgated by either a form (-3 or -5), OR via NOTAM action.
- If amended via form -3 or -5, most things can be changed as long as they do not change the routing or lower minimum altitudes (and some other details, shown in that table). Because they do not change routing or lower altitudes, many abbreviated amendments do not require flight inspection, so it's a big cost saver.
- If amended via NOTAM, the list of changeable things is even smaller, because:

The main difference between the two methods is that if done via a -3 or -5 form, the first the pilot will see of the changes is the actual published chart. If done via a NOTAM, the pilot will first see the NOTAM and have to manually edit the chart to include the NOTAMed changes. You can tell when the NOTAM is permanently amending the chart by the verbiage:

VOR RWY 18, Amdt 1...blah blah blah change change change...This is VOR RWY 18, Amdt 1A.

That statement at the end permanently changes the chart. A couple of chart cycles after the NOTAM is sent, the actual chart will be updated and the NOTAM canceled.

NOTAMs without the "This is" verbiage are "temporary" in nature, although may become permanent (actually a new NOTAM will be published with typically similar wording, but adding the "This is" verbiage).

Procedure name can be changed by either full amendment or abbreviated amendment using the forms. It cannot be changed by NOTAM action.

And then there are changes that can be made without an amendment at all! This is non-procedural stuff, typically frequencies or items on the airport diagram.

And then there are a few things which cannot be changed by any amendment process, the procedure must be canceled and a new one published (which would typically happen simultaneously, but that's the process) - for example, a LOC-only procedure adds a Glideslope. The LOC procedure would be canceled and an ILS OR LOC procedure published. Or a straight-in approach is changed to a circling-only approach (or vice versa, although that must be exceedingly rare).
 
Last edited:
MauleSkinner said:
“We’re from the FAA, and we’re here to help.”
Click to expand...

I really didn't mean it in that sense. While those kinds of changes, and the piecemeal way they roll out, may be interesting, they don't confuse me from an operational standpoint. "Oh, it says DME required here instead of there? Big deal." If I review the changes in charting and design which have taken place over the years, most have been for the better.

I always appreciate what I learn about the system from @RussR. Even if I need a weed eater to get though some of them.
 
RussR said:
See my blog post here, which covers this and a few other similar topics. Note this is from 2018 and the GPS notes have changed slightly.

http://cfiruss.blogspot.com/2018/05/goodbye-dme-hello-equipment.html?m=1
Click to expand...

Heh. Great article. So putting DME under Notes is supposed to resolve the confusion as to whether it's really required or not? Here's an example of the new and improved confusion from my backyard airspace. It's an approach that requires DME with non-DME minimums. I imagine a hapless crew inbound from TOMTA where the copilot is saying, "Whoops, we lost DME, go back up 40 feet. Ok, got it back now, you can go down 40. Oops, go back up 40, lost it again..., etc.":

05432VGA (skyvector.com)
 
Last edited:
dtuuri said:
QUOTE="RussR, post: 3354821, member: 8794"]See my blog post here, which covers this and a few other similar topics. Note this is from 2018 and the GPS notes have changed slightly.

http://cfiruss.blogspot.com/2018/05/goodbye-dme-hello-equipment.html?m=1
Click to expand...

Heh. Great article. So putting DME under Notes is supposed to resolve the confusion as to whether it's really required or not? Here's an example of the new and improved confusion from my backyard airspace. It's an approach that requires DME with non-DME minimums. I imagine a hapless crew inbound from TOMTA where the copilot is saying, "Whoops, we lost DME, go back up 40 feet. Ok, got it back now, you can go down 40. Oops, go back up 40, lost it again..., etc.":

05432VGA (skyvector.com)[/QUOTE]

My article discussed what's intended. Certainly it doesn't always work out as originally envisioned.

For that procedure, there is clearly an error. There should not be two sets of minimums since DME is required. If you are willing, please submit an aeronautical inquiry at the IFP Gateway regarding this issue.
 
RussR said:
For that procedure, there is clearly an error. There should not be two sets of minimums since DME is required. If you are willing, please submit an aeronautical inquiry at the IFP Gateway regarding this issue.
Click to expand...

I'll pass it on to the person who asked me if I could explain it. He's teaching a student, so a good time to teach error reporting.
 
RussR said:
Heh. Great article. So putting DME under Notes is supposed to resolve the confusion as to whether it's really required or not? Here's an example of the new and improved confusion from my backyard airspace. It's an approach that requires DME with non-DME minimums. I imagine a hapless crew inbound from TOMTA where the copilot is saying, "Whoops, we lost DME, go back up 40 feet. Ok, got it back now, you can go down 40. Oops, go back up 40, lost it again..., etc.":

05432VGA (skyvector.com)
Click to expand...

My article discussed what's intended. Certainly it doesn't always work out as originally envisioned.

For that procedure, there is clearly an error. There should not be two sets of minimums since DME is required. If you are willing, please submit an aeronautical inquiry at the IFP Gateway regarding this issue.[/QUOTE]
They must be tired of me sending those inquiries.
 
mcmanigle said:
Wow; even my favorite DME-arc-final approach at MTN doesn't have DME in the title anymore? That's kind of a shame...
Click to expand...

It's always been my opinion that approach should properly be titled "DME RWY 15", as the DME is providing the final course guidance, not the VOR. But with a grand total of 2 approaches like that, my recreational outrage is somewhat muted.
 
Very few people are going to opt for that approach in real life anymore, but it’s a great CRM exercise.
 
Yes, very cool approach. But can you imagine an instrument check ride where you're asked to fly that, with radial step-downs, through the full missed, which is a climbing turn to track a radial to turn onto another DME arc to a holding pattern on a two-radial (or radial-arc, but I imagine in the hold you're obligated to use the two radials that define it) intersection? Especially with raw data only, that would be a good check ride in and of itself o_O

(I didn't wind up doing my instrument check ride at MTN, but I did do a fair amount of my instrument training there.)
 
mcmanigle said:
Yes, very cool approach. But can you imagine an instrument check ride where you're asked to fly that, with radial step-downs, through the full missed, which is a climbing turn to track a radial to turn onto another DME arc to a holding pattern on a two-radial (or radial-arc, but I imagine in the hold you're obligated to use the two radials that define it) intersection? Especially with raw data only, that would be a good check ride in and of itself o_O

(I didn't wind up doing my instrument check ride at MTN, but I did do a fair amount of my instrument training there.)
Click to expand...
Most people I see tend to make raw data arcs in general, and this approach in particular, harder than they need to be.
 
MauleSkinner said:
Most people I see tend to make raw data arcs in general, and this approach in particular, harder than they need to be.
Click to expand...
True, I've always found arcs weirdly easy to fly (twist frequently, turn approx as much as you twist, turn a little more if the DME drifts up, delay your next turn a little if DME drifts down).

But, the transitions on that missed approach (blind climbing turn to radial to arc to radial/radial hold) would still give me the willies to do with foggles (never liked them) and an examiner in the other seat. A moving map would be nice for the nerves.
 
mcmanigle said:
But, the transitions on that missed approach (blind climbing turn to radial to arc to radial/radial hold) would still give me the willies to do with foggles (never liked them) and an examiner in the other seat. A moving map would be nice for the nerves.
Click to expand...
It’s a simple 90-degree turn both off the arc and back onto the other arc. It actually becomes easier when needle-ball-and-airspeed than with a full panel. ;)
 
RussR said:
Here's an example of the new and improved confusion from my backyard airspace. It's an approach that requires DME with non-DME minimums. I imagine a hapless crew inbound from TOMTA where the copilot is saying, "Whoops, we lost DME, go back up 40 feet. Ok, got it back now, you can go down 40. Oops, go back up 40, lost it again..., etc.":

05432VGA (skyvector.com)
Click to expand...

For that procedure, there is clearly an error. There should not be two sets of minimums since DME is required. If you are willing, please submit an aeronautical inquiry at the IFP Gateway regarding this issue.[/QUOTE]

Done.

"FAA Response:

Thanks for your inquiry. A T-NOTAM will be issued to correct the note to "DME REQUIRED FOR VOR PORTION", and a subsequent amdt will be accomplished to permanently correct the note and also remove the higher set of CIRC MINs that only applied to non-DME VOR aircraft. Have a good day."
​
But, I don't see why they didn't just remove the "DME Required" note and leave the rest of the chart alone.


​
 
Last edited:
mcmanigle said:
True, I've always found arcs weirdly easy to fly (twist frequently, turn approx as much as you twist, turn a little more if the DME drifts up, delay your next turn a little if DME drifts down).
Click to expand...
Perhaps even more than holding patterns, DME arcs are a poster child for how we complicate simple instrument maneuvers.

But for the good news, chances are most of us will never need to fly one for real. We have one near us (which is probably not going away), but I'm not using it as one of the nonprecision approaches for IPCs unless the pilot has real DME in the airplane.
 
midlifeflyer said:
Perhaps even more than holding patterns, DME arcs are a poster child for how we complicate simple instrument maneuvers.
Click to expand...
I think DME arcs have long been overcome by events in a world where area navigation rules. Other than keeping instrument students on their toes, they serve no real purpose anymore.

RF legs, on the other hand, offer procedure designers options to avoid terrain, obstacles or noise sensitive areas in ways that point-to-point navigation sometimes can't. But outside of RNP AR approaches, which are unavailable to light GA, they are hardly used at all. I wonder if those RF legs will become more commonplace in the future.

- Martin
 
Martin Pauly said:
I think DME arcs have long been overcome by events in a world where area navigation rules. Other than keeping instrument students on their toes, they serve no real purpose anymore.

RF legs, on the other hand, offer procedure designers options to avoid terrain, obstacles or noise sensitive areas in ways that point-to-point navigation sometimes can't. But outside of RNP AR approaches, which are unavailable to light GA, they are hardly used at all. I wonder if those RF legs will become more commonplace in the future.

- Martin
Click to expand...
I think RF legs are substantially different from DME arcs. RF legs are primarily to deal with terrain while DME arcs also have an efficiency piece. Take the one near me for example. Coming in (own nav) from the northeast on V454, the almost straight line arc between STASE and JISOT covers about 13 NM. Without it, we're at best looking at another 48 NM - and that's just to get to JISOT for the procedure turn. Literally makes the approach usable.

But unless the airplane has real DME, I'm not sure it serves any purpose even to keep pilots on their toes. Without GPS, it's easy. With GPS it's a no-brainer. The only time I can imagine flying it for real is with a GPS outage (you'll notice it's a MON airport). And, unless you have real DME on board, you can't fly it during a GPS outage. Still a little on the fence but that's why I'm planning to give it up for recurrent training in favor of a LOC approach (ILS NOTAM'd "GS UNUSBL") unless the airplane has DME.

upload_2023-2-2_10-27-49.png
 
midlifeflyer said:
I think RF legs are substantially different from DME arcs. RF legs are primarily to deal with terrain while DME arcs also have an efficiency piece.
Click to expand...

While dealing with terrain is definitely one of the big advantages of RF legs, they also play into efficiency if properly designed. Years ago I worked on a team with some representatives of the airlines and ATC. The airlines were all about using RF legs to shorten leg lengths (especially the final segment), and one of the reps had some data that showed how much money and fuel savings there were just by shaving a mile off a procedure at a busy airport, multiplied by thousands of operations. Assuming his data was correct, it was a pretty amazing number.

For example, Sacramento has no terrain issues, but has RF legs on the RNP approaches to each runway that make it so coming from the opposite direction an airplane rolls out on a 3 nm final instead of being vectored to intercept 3 miles outside a typical 5 nm FAF. That's probably 10 miles of time and fuel saved right there.

upload_2023-2-2_9-49-33.png
 
RussR said:
While dealing with terrain is definitely one of the big advantages of RF legs, they also play into efficiency if properly designed. Years ago I worked on a team with some representatives of the airlines and ATC. The airlines were all about using RF legs to shorten leg lengths (especially the final segment), and one of the reps had some data that showed how much money and fuel savings there were just by shaving a mile off a procedure at a busy airport, multiplied by thousands of operations. Assuming his data was correct, it was a pretty amazing number.

For example, Sacramento has no terrain issues, but has RF legs on the RNP approaches to each runway that make it so coming from the opposite direction an airplane rolls out on a 3 nm final instead of being vectored to intercept 3 miles outside a typical 5 nm FAF. That's probably 10 miles of time and fuel saved right there.

View attachment 114515
Click to expand...
Best part is, they pass that savings on to the flying public. :rolleyes:
 
Why are RF legs authorization-required when DME arcs are not? Is there some reason why they could not be included in the database of a WAAS GPS receiver?
 
Palmpilot said:
Why are RF legs authorization-required when DME arcs are not? Is there some reason why they could not be included in the database of a WAAS GPS receiver?
Click to expand...
On the technical side, they require autopilots that are beyond the capabilities of many light GA autopilots.
On the pilot side, they require contingency procedures to be developed to follow in the event of loss of navigation ability.

Among other things. These are just the ones that jumped out at me.
 
Palmpilot said:
Why are RF legs authorization-required when DME arcs are not? Is there some reason why they could not be included in the database of a WAAS GPS receiver?
Click to expand...

RF legs are supported in some installations of GTN and are in the database (see KRNO ILS Z or LOC Z Rwy 17R and KCRQ RNAV (GPS) X Rwy 24). They could technically be supported in the GNS, but this function was never enabled by Garmin, although Garmin did test it using GNS for an FAA Whitepaper evaluation. AC 90-105A includes Appendix L Additional Capabilities and specifies the limitations for use of RF legs. It defines what the AFMS must contain, but does not explicitly deal with part 91 authorization requirements for RF legs, but the AC has this general statement.

CHAPTER 7. OPERATIONAL APPROVAL PROCESS
7.1 Part 91 Operators. A letter of authorization (LOA) is not required for Title 14 of the Code of
Federal Regulations (14 CFR) part 91 operators (other than part 91 subpart K (part 91K)) except for oceanic operations (see Appendices E, F, and G) or if required in foreign airspace. Part 91
operators (other than 91K) should comply with the aircraft eligibility and operational guidance in this advisory circular (AC).
Click to expand...

The draft of AC 90-119 which will update several AC's including AC 90-105A has the following statement and hopefully when published it should clarify the requirements for Part 91:

10.5 A-RNP Operational Approval. Commercial operators require an A-RNP authorization. A-RNP operational approval is granted based on verification of pilot competency and aircraft eligibility. Part 91 operators do not require separate authorization to conduct A-RNP operations. Part 91 operators need only ensure that their aircraft is eligible for A-RNP operations and the pilot is competent to conduct the A-RNP operation.
Click to expand...

The GTN Xi AFMS has the following limitation, I have highlighted the phrase to point out that since Part 91 does not require authorization, RF legs may be used if the other limitations are met:

2.11 RF Legs
This STC does not grant operational approval for RF leg navigation for those operators requiring
operational approval. Additional FAA approval may be required for those aircraft intending to use
the GTN Xi as a means to provide RNP 1 navigation in accordance with FAA Advisory Circular AC
90-105A.

The following limitations apply to procedures with RF legs:

• Aircraft is limited to 180 KIAS while on the RF leg
• RF legs are limited to RNP 1 procedures. RNP AR and RNP <1 are not approved
• Primary navigation guidance on RF legs must be shown on an EHSI indicator with auto-slew
capability turned ON
• GTN Xi Moving Map, EHSI Map, or Distance to Next Waypoint information must be displayed to
the pilot during the RF leg when flying without the aid of the autopilot or flight director.
o The active waypoint must be displayed in the pilot’s primary field of view.
Click to expand...

and,

2.12.1 RNP 1.0 RF Leg Types
AC 90-105A states that procedures with RF legs must be flown using either a flight director or
coupled to the autopilot.

This STC has demonstrated acceptable crew workload and Flight Technical Error for hand flown
procedures with RF legs when the GTN Xi installation complies with limitation set forth in Section
2.11 of this document. It is recommended to couple the autopilot for RF procedures, if available,
but it is not required to do so. See section 4.5 of this manual to determine if this
capability is supported in this installation.
Click to expand...

The installation in my Bonanza meets the requirements and the following sections are checked in section 4.5:

The GTN Xi allows for the utilization of IFR procedures that include
RF (Radius to Fix) legs as part of RNP 1.0 capabilities.

◻ This installation is equipped to support coupled RF leg navigation up to RNP 1.0.
◻ This installation is equipped to support un-coupled RF leg navigation up to RNP 1.0.
Click to expand...
 
Palmpilot said:
Why are RF legs authorization-required when DME arcs are not? Is there some reason why they could not be included in the database of a WAAS GPS receiver?
Click to expand...
John gave a great answer above. "AR" (authorization required) raises the bar; instead of RNP 1.0 for which the Garmin GTNs do support RF legs, RNP AR goes down to 0.3 or even 0.1 NM. There just isn't much room for error, even if (or maybe I should say especially if) something goes wrong, like a GPS integrity issue of equipment failures. The RF legs per se aren't the problem; it's instrument procedure design which takes advantage of the extremely high accuracy assumptions which make RNP AR so tricky.

- Martin
 
You must log in or register to reply here.
Back
Top