GPS and DME Arc

P

pntbllr233

Pilot
Hey folks,

I have a few questions about using a Garmin GTN650 for a DME arc. I don't have a lot of experience with DME arcs, but the person I have been doing a lot of safety pilot flying with lately just got a 650 in his Mooney and is trying to get more experience doing these approaches. This model GPS is completely new to me, so I thought I would ask you guys a few things. How do you get your DME reading when all you have for DME is the GPS? Do you turn to the default navigation page and use that with the VOR being your "Direct to" and use that distance reading? That's sort of how I feel it would work and it's actually how we have been doing it. The owner was a little bummed when he found out he had this really nice GPS with the map display and everything and couldn't use it like that because the distance displayed on the map page isn't to the VOR, but rather the next waypoint (not always the VOR). I did a search and found a lot of older stuff saying this way of getting the DME could work, but I wasn't sure if anything has changed with the new GPS models such as the 650.

My next question is regarding the CDI in GPS vs. VLOC mode for a non-precision approach. The older posts I read said it was legal to fly the arc using the CDI in GPS mode and doing it that way versus the older 10/10 trick. My question comes when you finish up the arc and begin your final approach. Are you allowed to continue the approach with the CDI in GPS or does it have to be flown in VLOC? I feel like it has to be flown in VLOC because it's a VOR/LOC approach and also because it doesn't say anything about GPS on the approach plate. Some of the older posts I read said that for a VOR is has to be flown in VLOC with the GPS for situational awareness, but does it make any difference if it is a LOC approach with a DME arc? The owner switched it from VLOC to GPS mode while on the approach to see if anything changed, but the needle stayed the same. Also, when we got to the MAP we were easily able to identify it using GPS mode to show the change of the TO/FROM flag versus having to identify it using time. Is that something that's legal to do?

Sorry for the long post. I don't have a lot of experience with GPS, and have never used a 650 until now, so I wanted to see what everyone thought. Also, if anyone has any other tips or tricks for the Garmin 430 or the 650 that you feel makes life easier then please share for myself and everyone who might read. I told the owner I would check in to this and let him know, so I really appreciate the answers because you're helping us both out.

Mike

edit: the approach we used was the LOC 17 at KBVO with the DME arc from the west..
 

Attachments

First off:
AOPA (you are a member, right? right?) has an excellent "GPS for IFR ops" course from the Air Safety Foundation. Spend the money (if you aren't a member, and while you're doing that, go out and get their legal services plan too, because you might need it someday) and the time to watch it. I think I might just watch it again, because I consider it that good. See here, or a direct link if you are a member and logged in.

Completely unrelated: That chart burns my eyes; does your client use Jepps? iPad + JeppFD = awesomeness.

pntbllr233 said:
Hey folks,

I have a few questions about using a Garmin GTN650 for a DME arc. I don't have a lot of experience with DME arcs, but the person I have been doing a lot of safety pilot flying with lately just got a 650 in his Mooney and is trying to get more experience doing these approaches. This model GPS is completely new to me, so I thought I would ask you guys a few things. How do you get your DME reading when all you have for DME is the GPS? Do you turn to the default navigation page and use that with the VOR being your "Direct to" and use that distance reading? That's sort of how I feel it would work and it's actually how we have been doing it. The owner was a little bummed when he found out he had this really nice GPS with the map display and everything and couldn't use it like that because the distance displayed on the map page isn't to the VOR, but rather the next waypoint (not always the VOR). I did a search and found a lot of older stuff saying this way of getting the DME could work, but I wasn't sure if anything has changed with the new GPS models such as the 650.
Click to expand...
The arc itself must be a component of the procedure, and in the navigation database. GPS distance isn't equivalent to DME due to the lack of slant range. (Edit: See link below.) It's been ages since I flew a procedure with a DME arc that was in the Garmin database, so I don't remember what the presentation is like when established on the arc. I seem to recall that it'll do roll steering if you have an autopilot/flight director, though. Which is pretty sexy.

(stupidity omitted) By the way, DME arcs are easier than shooting fish in a barrel when you have an RMI. (I've not actually tried shooting fish in a barrel, but it sounds like something that would be trivially accomplished.)

My next question is regarding the CDI in GPS vs. VLOC mode for a non-precision approach. The older posts I read said it was legal to fly the arc using the CDI in GPS mode and doing it that way versus the older 10/10 trick. My question comes when you finish up the arc and begin your final approach. Are you allowed to continue the approach with the CDI in GPS or does it have to be flown in VLOC? I feel like it has to be flown in VLOC because it's a VOR/LOC approach and also because it doesn't say anything about GPS on the approach plate. Some of the older posts I read said that for a VOR is has to be flown in VLOC with the GPS for situational awareness, but does it make any difference if it is a LOC approach with a DME arc? The owner switched it from VLOC to GPS mode while on the approach to see if anything changed, but the needle stayed the same. Also, when we got to the MAP we were easily able to identify it using GPS mode to show the change of the TO/FROM flag versus having to identify it using time. Is that something that's legal to do?
Click to expand...
You can use GPS for primary navigational guidance for the final segment on a nonprecision approach if the procedure is in the GPS database, and:
(1) the procedure title reads something like VOR DME (GPS) Runway (___), commonly called an overlay, or:
(2) the procedure title reads RNAV (GPS) Runway (__), commonly called a standalone RNAV approach.

(2) should be obvious, of course, but sometimes things bear repeating.

You can use GPS for navigation on the initial segment (e.g. the DME arcs in the procedure you attached) provided that the procedure is in the database. On that procedure you attached, the pilot must be using ground-based navigation no later than the final approach fix (DEWIE/LOM inbound). The pilot may also execute the missed approach using GPS. The localizer and all other required ground equipment for this approach must be operative, and the pilot must select VLOC on the CDI not later than the final approach fix inbound. The Garmin boxes tend to be pretty good about reminding you about this—if you load a full ILS into the flight plan, it will remind you that the GPS is for "monitoring" only.

Sorry for the long post. I don't have a lot of experience with GPS, and have never used a 650 until now, so I wanted to see what everyone thought. Also, if anyone has any other tips or tricks for the Garmin 430 or the 650 that you feel makes life easier then please share for myself and everyone who might read. I told the owner I would check in to this and let him know, so I really appreciate the answers because you're helping us both out.
Click to expand...
Canned flight plans are wonderful things; storing plans that you use regularly in the 430 makes for less sitting on the ramp/in the runup pad twisting the knobs.

Always glance at the annunciator above the suicide switch (the CDI button) to make sure that you are, in fact, navigating with what you mean to navigate. The unit's sensitivity on the 430 is also something to watch (if you're doing an LPV approach, you need to see LPV when approaching the final segment and so on). I don't know where it is on that newfangled touchscreen beast.
 
Autothrust Blue said:
The arc itself must be a component of the procedure, and in the navigation database. GPS distance isn't equivalent to DME due to the lack of slant range.
Click to expand...

Do you have a reference for the first sentence? The AIM says with a suitable RNAV system I can substitute DME with RNAV and I can use it to fly an arc. The point I'm using for DME certainly has to be in the database, but I'm not seeing where the arc has to be.
 
Ian J said:
Do you have a reference for the first sentence? The AIM says with a suitable RNAV system I can substitute DME with RNAV and I can use it to fly an arc. The point I'm using for DME certainly has to be in the database, but I'm not seeing where the arc has to be.
Click to expand...
I don't, off the top of my head. I'll look around though.
 
Autothrust Blue said:
I don't, off the top of my head. I'll look around though.
Click to expand...
Ian J said:
Do you have a reference for the first sentence? The AIM says with a suitable RNAV system I can substitute DME with RNAV and I can use it to fly an arc. The point I'm using for DME certainly has to be in the database, but I'm not seeing where the arc has to be.
Click to expand...
Brains, I has them. Actually I don't. I shouldn't answer these questions before my first cup of coffee.

See here.

Relevant part:
DME arcs associated with instrument approaches may be flown using GPS distance provided the DME transmitter, on which the arc is based, is identified in the GPS database (see Figure A).
Click to expand...
So never mind, I had it backwards. Like I said, AOPA knows a lot more about this than I do.
 
Autothrust Blue said:
Brains, I has them. Actually I don't. I shouldn't answer these questions before my first cup of coffee.

See here.

Relevant part:

So never mind, I had it backwards. Like I said, AOPA knows a lot more about this than I do.
Click to expand...

Cool... just making sure I haven't been doing it wrong!
 
Ian J said:
Cool... just making sure I haven't been doing it wrong!
Click to expand...
"Must be in database" must be a work thing, not a 91 thing. You all can fly it inverted in a four-G dive with a handheld (okay, well not really, but you get the point) as far as I and the FAA care. :D
 
Autothrust Blue said:
"Must be in database" must be a work thing, not a 91 thing. You all can fly it inverted in a four-G dive with a handheld (okay, well not really, but you get the point) as far as I and the FAA care. :D
Click to expand...

So, my ex-student found his way to you, I see....
 
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