GPS in lieu of DME

[lhornaday]

When you're shooting a VOR/DME with a G-430 as the DME source, is it mandatory to have the GPS tracking to the listed VOR to get the DME? Reason being it that I have a student who likes to do the GPS overlay and get the distance count down to each fix. But everything i've read, and the companies i've worked for say no.

Next, how are instrument examiners with students using electronic charts?

 

[Douglas]

When it is overlayed, does it tell him the distance he needs to comply the IAP?

 

[MidlifeFlyer]

What do you mean by "the GPS overlay"? A GPS overlay approach chart will be titled "VOR/DME OR GPS." If it says that, they he just loads in the GPS approach and flies that.

But it you mean, "he flies the approach he loaded after the warning that he's not supposed to," well he's supposed to have the GPS tuned to the VOR and use that read.

A DPS should't care about whether the charts are paper or electronic. But whether a particular one will care is another story and I'd hesitate to make any genarlizations. Ask the DPE you plan to use.

 

[ppragman]

I've used a GPS overlay before, and been right over a fix telling me to turn, and had the controller say, "hey, you're about 2 miles off course you gonna turn yet?" Slant range has something to do with that, and GPS doesn't give you that.

 

[KSCessnaDriver]

Next, how are instrument examiners with students using electronic charts?

Are charts legally required?

 

[mshunter]

It doesn't matter if you you the "-D->" or tune to the nearest page. You just need a readout of distance from an IFR approved GPS.


With a G430, I don't see why you couldn't do an overlay as long as you can determine the distance from what ever fix your using for DME. I know it displays the "For monitoring use only," But all your doing is monitoring the distance anyways. In essence, you could turn to the FPL page and watch your distances right there.

 

[esa17]

NOS charts will have a distance in parenthesis "(5)" that is the straight line distance between fixes which can aid in using a GPS in lieu of DME.

 

[CoffeeIcePapers]

I think we are confusing terms. An overlay approach is what Midlifeflyer referred to.

We also commonly refer to it as an overlay when we load the GPS for the VOR Procedure like mshunter said. This is the way I prefer to do it. It standardizes everything. As long as you have the CDI course selected and can verify the waypoints, any way you do it is fine.

 

[The Gardener]

Are charts legally required?

Not for part 91 operations.

I've been doing electronic nav logs with my students on IFR x/c's. Being able to find common routes and plan things easily is a lot more practical for the IFR world. The examiners I use have had no problems with it.

I've been using an Ipad/foreflight recently and I'm 100% convinced that it is practical and usable. Now I just need to pony up $750.

 

[Roger, Roger]

When doing a VOR approach, I've always just used the VOR CDI for course guidance and the GPS countdown to the next fix for distance. Haven't heard of it being taught any other way.

 

[KSCessnaDriver]

Not for part 91 operations.

I've been using an Ipad/foreflight recently and I'm 100% convinced that it is practical and usable. Now I just need to pony up $750.

Yup. I run a Sony PRS-505 with just the approach plates on it, and still carry paper en-routes. Makes things so much easier for organization. Couple that with electronic flight planning and IFR flying changes totally. I quickly learned that even the basic DUAT/DUATS flight planner is really accurate, as long as you enter your data right. I spent 10 hours flying an IFR flight one day, and total, it was off like 10 minutes over 4 legs.

 

[Mike H]

When you're shooting a VOR/DME with a G-430 as the DME source, is it mandatory to have the GPS tracking to the listed VOR to get the DME? Reason being it that I have a student who likes to do the GPS overlay and get the distance count down to each fix. But everything i've read, and the companies i've worked for say no.

Depends on how you're flying the approach. If you're flying it as a VOR approach, the correct way is to have the GPS showing the distance from the VOR. If you're flying it as a GPS approach, it's correct to use it to show distance to the next waypoint. Some DPEs are very picky about this, others aren't.

 

[Roger, Roger]

Depends on how you're flying the approach. If you're flying it as a VOR approach, the correct way is to have the GPS showing the distance from the VOR.

Are you sure that is correct? It's been a while, but if memory serves that is not what the Garmin literature says. Can't say for other makes of IFR-certified GPSs.

 

[CoffeeIcePapers]

Depends on how you're flying the approach. If you're flying it as a VOR approach, the correct way is to have the GPS showing the distance from the VOR. If you're flying it as a GPS approach, it's correct to use it to show distance to the next waypoint. Some DPEs are very picky about this, others aren't.

The problem is that there is no standardized way, at least from what I have seen. Different GPSs use different procedures. Like Roger Roger said, the Garmin products suggest you load the procedure in the GPS and make sure that you have the CDI source selected properly.

http://www8.garmin.com/manuals/GNS430_PilotsGuide.pdf

It doesn't matter how you load it, as long as you are able to know that you are at the waypoint/DME fix.


The Instrument Flying Handbook lists a few ways to do it on 7-29:

To Determine Aircraft Position Over a DME Fix:
1. Verify aircraft GPS system integrity monitoring
is functioning properly and indicates satisfactory
integrity.
2. If the fix is identified by a five-letter name which is
contained in the GPS airborne database, select either
the named fix as the active GPS WP or the facility
establishing the DME fix as the active GPS WP. When
using a facility as the active WP, the only acceptable
facility is the DME facility which is charted as the one
used to establish the DME fix. If this facility is not in
the airborne database, it is not authorized for use.
3. If the fix is identified by a five-letter name which is not
contained in the GPS airborne database, or if the fix is
not named, select the facility establishing the DME fix
or another named DME fix as the active GPS WP.
4. When selecting the named fix as the active GPS WP,
a pilot is over the fix when the GPS system indicates
the active WP.
5. If selecting the DME providing facility as the active
GPS WP, a pilot is over the fix when the GPS distance
from the active WP equals the charted DME value, and
the aircraft is established on the appropriate bearing
or course

 

[Mike H]

Are you sure that is correct? It's been a while, but if memory serves that is not what the Garmin literature says. Can't say for other makes of IFR-certified GPSs.

Am I totally sure it's correct, no. Am I totally sure that's what the DPE wanted to see when I did my ME add-on, yeah, I'm positive on that

 

[lhornaday]

Re: mojo6911

Am I totally sure it's correct, no. Am I totally sure that's what the DPE wanted to see when I did my ME add-on, yeah, I'm positive on that

I'm am going with your conclusion also. What mojo6911 quoted makes it seem that it isn't but there is more to this situation.

With a VOR/DME the GPS is there for advisory only. The GPS DME readout is there to meet the need for the approach. I think it has to be tuned to the same facility as charted.

Flying commercially, I use to hold a VOR DME readout but then load the approach as an RNAV or visual in the FMS. There would also be a bearing pointer to the VOR to meet the lateral navigation requirement.

But I was trying to make it easy on my instrument student. If it wasn't required, I wasn't going to insist.

 

[CoffeeIcePapers]

Re: mojo6911

I

With a VOR/DME the GPS is there for advisory only.

That isn't true. The GPS is replacing the DME requirement for the approach, so it is required and is there for much more than advisory only.

 

[Roger, Roger]

Re: mojo6911

That isn't true. The GPS is replacing the DME requirement for the approach, so it is required and is there for much more than advisory only.

:yeahthat:

Also, I'm pretty sure (can't find it at the moment though) that Garmin says "Thou shalt have the approach loaded and activated when flying a VOR/NDB approach requiring DME". Can't find a reference for it now.

Finally, keep in mind that if you just use your GPS distance readout, it may not match the DME slant range readout. Therefore, using the pre-loaded waypoints for the approach (which WILL match the location of the DME slant range waypoints) in the database is the more accurate and correct way to fly the approach.

 

[lhornaday]

Re: mojo6911

That isn't true. The GPS is replacing the DME requirement for the approach, so it is required and is there for much more than advisory only.

Come on now I'm not that dumb. I'm referring to the lateral display, not the DME.

 

[lhornaday]

Here is another concern...

Flying a VOR/DME approach that starts with a DME arc. Do you load the approach into the GPS and "picture nav" around the arc or set the GPS to readout the DME from the primary nav aid?