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View Full Version : DME question


RG1979
01-16-2018, 07:03 AM
I have a DME question regarding the Garmin 1000 (G1000H).
The NAV1 and NAV2 needles on the PFD will give you a distance to the selected NAV source (Airport, VOR, ILS, etc). To my understanding this is a GPS distance.
The G1000 in the aircraft does not have the separate DME softkey, so that tells me I don't have the DME equipment on board.

When giving a 61.57(d) as a CFII, do I have to make the pilot do a DME/ARC (IFR PTS)?
The note in the PTS says that if the aircraft is not equipped with DME I don't have to do the approach.

In other words, does the distance I see on the PFD substitute DME?
Can I legally use it that way?

Anyone have any sources?

Thanks!


JohnBurke
01-16-2018, 08:16 AM
I have a DME question regarding the Garmin 1000 (G1000H).
The NAV1 and NAV2 needles on the PFD will give you a distance to the selected NAV source (Airport, VOR, ILS, etc). To my understanding this is a GPS distance.
The G1000 in the aircraft does not have the separate DME softkey, so that tells me I don't have the DME equipment on board.

When giving a 61.57(d) as a CFII, do I have to make the pilot do a DME/ARC (IFR PTS)?
The note in the PTS says that if the aircraft is not equipped with DME I don't have to do the approach.

In other words, does the distance I see on the PFD substitute DME?
Can I legally use it that way?

Anyone have any sources?

Thanks!

AIM 5-3-13 https://www.faa.gov/air_traffic/publications/media/AIM.pdf

6. Use of RNAV Distance in lieu of DME Distance. Substitution of RNAV computed distance to or from a NAVAID in place of DME distance is permitted when holding. However, the actual holding location and pattern flown will be further from the NAVAID than designed due to the lack of slant range in the position solution (see FIG 5−3−7). This may result in a slight difference between RNAV distance readout in reference to the NAVAID and the DME
readout, especially at higher altitudes. When used solely for DME substitution, the difference between RNAV distance to/from a fix and DME slant range distance can be considered negligible and no pilot action is required.


You're not required to have the applicant demonstrate an approach with a DME arc. If you use GPS in lieu of DME, the waypoints used must be retrievable from the current database of an IFR-aproved GPS installation.

RG1979
01-16-2018, 09:10 AM
Thanks for the source John!

It might be nitpicking, but it says "when holding". So does this apply to a hold only, or also an approach?


RG1979
01-16-2018, 09:28 AM
I think I found the answer on page 1-1-29 of the AIM. This table applies to approaches.

JohnBurke
01-16-2018, 12:48 PM
Thanks for the source John!

It might be nitpicking, but it says "when holding". So does this apply to a hold only, or also an approach?

You're not nitpicking. That reference was to holding. It applies to all other phases of operation too. If operating under IFR, the GPS installation must be approved for that phase, and the fix must be retrievable from the database. The salient observation in the link was that the DME slant range difference is considered negligible.

GPS may also be used in lieu of NDB fixes.

You're still not required to have the applicant demonstrate every possible type of approach, during an instrument proficiency check.

Can you use the GPS distance to the primary facility fix for the arc? Yes, so long as the approach and the fix are in the database and the GPS installation is approved for the operation.

You indicated that you don't know if DME is installed (did you look in the equipment list, or check for the antenna?). You should know if the aircraft has that equipment, or not. DME as a sensor input, especially if autotuned by the system, may not have an independent control, but may still be installed. It should be found in your equipment list.

JamesNoBrakes
01-16-2018, 09:13 PM
There are also some advisory circulars and other guidance that go into detail explaining what GPS can substitute for and how you can use it up to the FAF on an approach and then again for the missed segment.

Except for many legacy FMS boxes, where you don't really see the stand-alone equipment anyway, traditional DME receivers are becoming very rare, once you have a double GPS setup you can dump some weight by getting rid of the DME, and as explained, as long as it's in your GPS database and current, it's generally no problem to use.

RG1979
01-17-2018, 06:34 AM
You indicated that you don't know if DME is installed (did you look in the equipment list, or check for the antenna?). You should know if the aircraft has that equipment, or not. DME as a sensor input, especially if autotuned by the system, may not have an independent control, but may still be installed. It should be found in your equipment list.

It's actually a level D sim I'm talking about ;)

PerfInit
01-17-2018, 07:31 AM
Check the “T001-A” form for the FSTD. Usually located in a binder near the sim (often on a podium prior to the “gangway”. This form, in addition to the Statement of Qualification (SOQ) will help you determine the capability of the sim in question. Does the IOS panel have the capability to simulate a failure of the DME? Perhaps ask the “sim tech” as they can “dig” deeper and give you a reliable answer.

JohnBurke
01-17-2018, 05:57 PM
It's actually a level D sim I'm talking about ;)

With a multi-sensor system and display, you're not so much concerned about the source of the data as what you're given. Many units combine VOR information, DME, DME-DME, GPS, IRS/INS, etc; it only outputs nav data. You can delve into the system to explore sensors and sensor availability, but unless the system advises you that the input isn't available or is questionable, all you really care about is whether you have nav guidance.

You may be on an approach with a marker or NDB or DME inoperative, yet your system provides GPS data which replaces the missing elements and gives you what you need to fly the approach. So long as the required navigation performance is available, the particular source of the data becomes ancillary so long as it's valid data.