DME Required... really?

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malibugrif

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malibu
This is an answer that I want to be on the wrong side of. A pilot at KMYF asked if the KMYF ILS LOC 28R approach which is noted as “DME Required” applied to his G1000 equipped airplane. My first thought was although the plane has no DME, it does have a panel mounted, database current, certified GPS that’s at least as accurate and reliable as DME. However, as I research the issue, I’ve come to the conclusion that no, the plane must be equipped with DME. Please tell me where my logic goes astray.

1) The approach is not marked GPS. As we know from the Sept 22 discussion on this board, AIM 1-1-19(g), tells us , “all the approaches that can be used by GPS now contain “GPS” in the title”. So that would seem to prohibit the use of the GPS in lieu of DME.

2) What about AIM 1-2-3(c), which allows the GPS to identify a DME fix where the airplane is not equipped with DME. However, note 3 specifically indicates that “Pilots may not substitute [GPS] for the navigation aid providing lateral guidance for the final approach segment.” In the case of KMYF, one of the DME waypoints is the FAF, part of the final approach segment.

3) Finally, turning to the Garmin’s AFMS, a limitation on the GPS states, "Accomplishment of ILS, LOC ... or any other type of approach not approved for GPS overlay with the G1000 GPS receiver is not authorized.” That seems definitive to me, that if he needs DME to accomplish the approach, he can’t do so with the G1000.

Again, logic tells me that if the approach is in the database, which it is, the pilot should be able to fly the approach using the GPS database for the purpose of identifying the DME waypoints. Yet, I'm coming to an opposite conclusion. (In your answer, please ignore there exists a perfectly good RNAV approach into this same runway. The question is really about the DME “requirement”.)
 
malibugrif said:
2) What about AIM 1-2-3(c), which allows the GPS to identify a DME fix where the airplane is not equipped with DME. However, note 3 specifically indicates that “Pilots may not substitute [GPS] for the navigation aid providing lateral guidance for the final approach segment.” In the case of KMYF, one of the DME waypoints is the FAF, part of the final approach segment.
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My guess is that the FAA does not intend the word "lateral" to include along-track distance.

I have no clue about what Garmin intended.
 
However, note 3 specifically indicates that “Pilots may not substitute [GPS] for the navigation aid providing lateral guidance for the final approach segment.” In the case of KMYF, one of the DME waypoints is the FAF, part of the final approach segment...
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For the approach in question, the navigation aid providing lateral guidance for the final approach segment is the localizer, so you must use a real nav radio and not the GPS, to drive the little needle.

The DME is not "lateral guidance", and as long as your GPS is an IFR-approved installation, current database, etc, it can certainly serve as a substitute for DME.

Where your logic is going wrong is that all of the references you provide are telling you that you can't use GPS to substitute for the localizer, but none are telling you that you can't use it to substitute for the DME.
-harry
 
mantakos said:
Where your logic is going wrong is that all of the references you provide are telling you that you can't use GPS to substitute for the localizer, but none are telling you that you can't use it to substitute for the DME.
-harry
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That's exactly right.

"Lateral" navigation using DME past the FAF is not something you'll see much, if at all, in the U.S. At least I haven't seen a DME/DME approach here.

-Felix
 
Thank you for the quick responses. I can accept that "lateral" as used in 1-2-3, may not include along track distances but I'm having a real problem with the AFMS limitation.

Look at AIM 1-1-9 that tells us that an Instrument Landing System (emphasis on "system") consists of three parts: 1) guidance information provided by the localizer, glide slope, 2) range information provided by marker beacon, DME, and 3)visual information such as touch down and runway lights. When Garmin says that the receiver is not authorized for use on this (non GPS) ILS approach, I don't see how you can argue that Garmin only means the guidance portion of the approach. While I like your opinion Harry, I need some authority.

Malibu
 
malibugrif said:
Look at AIM 1-1-9 that tells us that an Instrument Landing System (emphasis on "system") consists of three parts: 1) guidance information provided by the localizer, glide slope, 2) range information provided by marker beacon, DME, and 3)visual information such as touch down and runway lights. When Garmin says that the receiver is not authorized for use on this (non GPS) ILS approach, I don't see how you can argue that Garmin only means the guidance portion of the approach. While I like your opinion Harry, I need some authority.

Malibu
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The thing is that this isn't a hotly debated topic at all. What Garmin is saying is that you can't substitute GPS for the Localizer. In other word, you can't substitute GPS for primary guidance provided by the Localizer. This doesn't mean that you can't substitute GPS for DME for the purpose of identifying fixes.

Another way of looking at it - you can't fly this approach at all if you only had GPS and no LOC equipment. Makes sense?

-Felix
 
You may be correct that Garmin means that the G1000 cannot be substituted for the localizer and that would have been simple to write.

But Garmin didn’t write that. Instead the limitation is clear: Accomplishment of a non-GPS ILS is not authorized. To me, that’s plain: you can’t use the Garmin for primary navigation on any part of the ILS approach. (It goes without saying that you can use anything you want for supplemental navigation.)
 
malibugrif said:
You may be correct that Garmin means that the G1000 cannot be substituted for the localizer and that would have been simple to write.

But Garmin didn’t write that. Instead the limitation is clear: Accomplishment of a non-GPS ILS is not authorized. To me, that’s plain: you can’t use the Garmin for primary navigation on any part of the ILS approach. (It goes without saying that you can use anything you want for supplemental navigation.)
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I can't stop you from believing that, but I can guarantee the FAA won't bust you if you use your G1000 system to handle the DME requirement in any situation other than the VOR/DME or TACAN Z Rwy 15 approach to KMTN, where the final segment is a DME arc (the only such approach in the country AFAIK) so you must use DME for lateral guidance on the final segment.
 
Horse. Water. Please drink! Ron and Felix and I and others on this forum have beaten this topic to death. For a while the AIM was "ahead" of the rest of guidance but that was recently fixed. You can absolutely/positively/no-two-ways-about-it punch in the appropriate fix on your G1000, set it up as RMI pointer 1 or 2 while your HSI is set to the ILS, and use the distance given as a substitute for DME. In fact, if you load the approach, I wouldn't be surprised if the G1000 didn't do that for you automatically!

So congratulations, you're wrong! (which is what you wanted to be in the first place)
 
Tim and Ron,

Thank you for weighing in. I have respect for your work on this board and know that you both give thought to your posts.

What I haven't read on this message board is any discussion of Garmins' AFMS limitation. What is meant by Garmin's limitation: that the G1000 is not authorized for use on non-overlay ILS, LOC approaches? (This same limitation appears on the 430 and 530 products.)

Malibu
 
What that means is that you cant use GPS as your nav source when flying an approach where lateral guidance is provided by a localizer. Essentially, it's saying (in Garminese) the same thing the AIM says, and is a further reminder to switch the CDI source if it doesn't happen automagically.

The "non-overlay" wording is probably there in case they ever approve GPS to overlay a localizer (for an SDF or offset LDA, for example) in the future. Someday you may see an approach titled "LDA or GPS 19" or "LOC or GPS 27" and if that ever comes to pass Garmin won't have to rewrite it's supplement. When LAAS comes along, this is possible, perhaps even probable.
 
What I haven't read on this message board is any discussion of Garmins' AFMS limitation.
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It's poorly worded.

Look through the Garmin documentation, I'll bet you a quarter that they document how to use the unit in such a manner.
-harry
 
Soo does an IFR GPS fulfil the DMR requirement above 24,000'?????
 
On the G1000, EVERY VOR you tune becomes a VOR/DME. If you get a signal, the system will display GPS-derived distance.
 
TMetzinger said:
Horse. Water. Please drink! . In fact, if you load the approach, I wouldn't be surprised if the G1000 didn't do that for you automatically!

So congratulations, you're wrong! (which is what you wanted to be in the first place)
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Tim, you are correct, IIRC,
If you Select the ILS Approach into the G1000, it will provide "GPS lateral and DME guidance" to all of the fixes and legs leading up to the FAF or ILS Glideslope intercept. It will even preload the ILS (LOC) frequency into NAV1. Outside the FAF it will alert you and provide transition from GPS CDI Deflections to LOC CDI Deflections (Lateral Guidence) on the HSI portion of the G1000 PFD and continue to provide "DME or Distance" information to the DH. NAV1 is now primary for Lateral Navigation, not GPS and the words on the HSI will state (and I think the CDI display changes from magenta (GPS) to Green (VOR/LOC1)

On top of all of that, the Missed Approach Procedure will be preloaded and ready to fly. If you go Missed at DH, press the "Suspend" button and it will provide GPS lateral Navigation for the Missed Approach Procedure all the way and into the Missed holding pattern. Be careful about when you hit the "Suspend", some Missed procedures require a climb before turning, normally initiate the climb, and when reaching the stated altitude to turn, then hit suspend.

The above "Suspend" for MAProcedure varies by approach and a full understanding and check out of G1000 operations is highly recommended before flying in true instrument conditions.
 
Okay,

hate to butt in, but I need a more basic clarification....

Can one use a GNS-XLS for the distance measuring on an approach? This is a VFR only panel mounted GPS device, which clearly means no instrument approach use other than for situational awareness, but how about the distance?

Perhaps this has already been answered in the thread, but I'm kind of slow and need it spelled out.:yikes:

Thanks.
 
TeaSea said:
Okay,

hate to butt in, but I need a more basic clarification....

Can one use a GNS-XLS for the distance measuring on an approach? This is a VFR only panel mounted GPS device, which clearly means no instrument approach use other than for situational awareness, but how about the distance?

Perhaps this has already been answered in the thread, but I'm kind of slow and need it spelled out.:yikes:

Thanks.
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NO.

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What, you want details? In a nutshell, you can only use an IFR gps to substitute for DME when operating under IFR.
 
...and the documentation for Tim's answer is in the AIM, section 1-1-19, Table 1-1-6. Use of a VFR-only GPS for IFR purposes other than situational awareness is (like "any reproduction, reuse, or rebroacast of this telecast without the approval of the Commissioner") prohibited.
 
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