Ad Hoc DME arc on GTN750

DesertNomad

DesertNomad

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DesertNomad
If I get a departure instruction:

Runway heading to intercept the 220 radial off XYZ (VOR).

Fly 5nm DME Arc south to 150 radial then ABCDE (fix)

How can I build that?
 
You mean with a magenta line? I'm not sure.

In a pinch you can get the distance by pressing "direct to" the VOR and then "twist and turn" like the old days either using the Nav radio or OBS.

One of the selectable user fields is bearing and range to a Navaid which would work too.

I'm not 100% sure but I don't think ATC assigns unpublished DME arcs. Any DME arc you would get would be in the GTN's database (I think).
 
Is this an academic question, or were you really issued such a clearance?

If this is the routing contained in a SID, you should be able to just load it from the database. Otherwise, yuck. Say to ATC, "are you kidding me? This is 2022."

But I'm not aware of a way to "build it" in the GTN750. If I had to, I'd just fly it in OBS mode I guess. No need to use the actual VOR signal, but I'd at least fake it. Although on second thought, using the actual VOR might be easier.
 
DesertNomad said:
If I get a departure instruction:

Runway heading to intercept the 220 radial off XYZ (VOR).
Click to expand...
...and then? Hang there in space?

what I mean is, whether it can be done at all or whether it is worth doing (there are tasks where VOR is easier) depends on context. Is it part of an airway you can load? Is the 220 radial going anywhere, perhaps an intersection or waypoint? Are you being instructed to intercept inbound or outbound?
 
Walboy said:
I'm not 100% sure but I don't think ATC assigns unpublished DME arcs. Any DME arc you would get would be in the GTN's database (I think).
Click to expand...

This is more for a CFII checkride scenario. I am not sure that such a clearance could realistically be issued. I am pretty sure the 750 can't do it - it'd be nice if it could build it like it builds ad hoc holds.
 
DesertNomad said:
This is more for a CFII checkride scenario. I am not sure that such a clearance could realistically be issued. I am pretty sure the 750 can't do it - it'd be nice if it could build it like it builds ad hoc holds.
Click to expand...

As stated earlier, I think the OBS mode would be the simplest. It would be pretty easy to fly a runway heading until you intercept the magenta line representing the 220 radial, then turn inbound or outbound depending where you are relative to 5 mn.

I quickly looked in a GTN manual and didn't see a way to "build" a DME arc. The manual is dated though and there have been software updates that may have included it like building a hold.
 
Can todays IR pilots even do a proper arc the old fashioned way??

To be honest, I know I would struggle. I could probably pull it off, but would have to think about it a bit.
It’s not an easy thing if thrown at you at the last second.
 
DesertNomad said:
This is more for a CFII checkride scenario. I am not sure that such a clearance could realistically be issued. I am pretty sure the 750 can't do it - it'd be nice if it could build it like it builds ad hoc holds.
Click to expand...
Not even checkride. From the instrument ACS.

Operational Requirements, Limitations, & Task Information
V. Navigation Systems
While the applicant is expected to be able to fly DME Arcs, they may be selected for testing only if they are charted and available​

I can't even imagine ATC making up an arc. Even their ad hoc holds tend to be direct entries on the course you are already flying because they are simple and do the separation job.

The outbound radial to nowhere is a different issue. Sort of a basic limitation. GPS "thinks" in terms of "to" something. It's not really designed to navigate "from" somewhere without a "to." The Garmins can sort of do it in OBS mode - they paint a white line extending from the OBS course created to the waypoint. The white line will be reflected in the CDI although it will not turn magenta without a "to" connection,
upload_2022-10-5_7-33-4.png
 
Kritchlow said:
Can todays IR pilots even do a proper arc the old fashioned way??

To be honest, I know I would struggle. I could probably pull it off, but would have to think about it a bit.
It’s not an easy thing if thrown at you at the last second.
Click to expand...
You gotta find an airplane with DME. That can sometimes be difficult in a world of GPS and glass.

it's actually one quibble I have with the FAA allowing GPS to be primary on a VOR approach (so long as you have raw data displayed). I think it's completely unrealistic. When would one actually fly a VOR approach unless there was a GPS failure? I know they exist but they are rare.
 
OBS to intercept and direct to the fix, then would bring up waypoint information (which gives updated distance from waypoint), tighten the turn if it shows 5.1 and straighten the turn if it shows 4.9.
Or do you want the autopilot flying the plane?
 
MooneyDriver78 said:
OBS to intercept and direct to the fix, then would bring up waypoint information (which gives updated distance from waypoint), tighten the turn if it shows 5.1 and straighten the turn if it shows 4.9.
Or do you want the autopilot flying the plane?
Click to expand...
I think he wants it to be painted on the screen and receive positive course guidance around the arc ("tun left 230 now"), not just use the distance readout. But yeah, if that's what he wants, you've described the "old school" method using new equipment.
 
midlifeflyer said:
I think he wants it to be painted on the screen and receive positive course guidance around the arc ("tun left 230 now"), not just use the distance readout. But yeah, if that's what he wants, you've described the "old school" method using new equipment.
Click to expand...

Ahhh…child of the magenta.
 
midlifeflyer said:
You gotta find an airplane with DME. That can sometimes be difficult in a world of GPS and glass.

it's actually one quibble I have with the FAA allowing GPS to be primary on a VOR approach (so long as you have raw data displayed). I think it's completely unrealistic. When would one actually fly a VOR approach unless there was a GPS failure? I know they exist but they are rare.
Click to expand...
Because it’s fun??
 
midlifeflyer said:
You gotta find an airplane with DME. That can sometimes be difficult in a world of GPS and glass.

it's actually one quibble I have with the FAA allowing GPS to be primary on a VOR approach (so long as you have raw data displayed). I think it's completely unrealistic. When would one actually fly a VOR approach unless there was a GPS failure? I know they exist but they are rare.
Click to expand...

It's because most people are more familiar/comfortable with their GPS than they are VOR.
There are still airports that have VOR approaches only, I'd prefer to fly those via the GPS than use the actual VOR personally (as I assume most people would)
 
You could do it using the GPS as the DME and using the VOR to do the classic turn 10 degrees, fly 10 degrees, twist 10 degrees.
 
Justin Brady said:
It's because most people are more familiar/comfortable with their GPS than they are VOR.
There are still airports that have VOR approaches only, I'd prefer to fly those via the GPS than use the actual VOR personally (as I assume most people would)
Click to expand...
I haven't seen that. Got some US examples?
 
midlifeflyer said:
Not even checkride. From the instrument ACS.

Operational Requirements, Limitations, & Task Information
V. Navigation Systems
While the applicant is expected to be able to fly DME Arcs, they may be selected for testing only if they are charted and available​

I can't even imagine ATC making up an arc. Even their ad hoc holds tend to be direct entries on the course you are already flying because they are simple and do the separation job.

The outbound radial to nowhere is a different issue. Sort of a basic limitation. GPS "thinks" in terms of "to" something. It's not really designed to navigate "from" somewhere without a "to." The Garmins can sort of do it in OBS mode - they paint a white line extending from the OBS course created to the waypoint. The white line will be reflected in the CDI although it will not turn magenta without a "to" connection,
View attachment 111205
Click to expand...
I was thinking ATC can issue impromptu DME Arcs. I know there was a time when they could. But I can’t find it anywhere in the current 7110.65.
 
luvflyin said:
I was thinking ATC can issue impromptu DME Arcs. I know there was a time when they could. But I can’t find it anywhere in the current 7110.65.
Click to expand...
That's why I added that I can't imagine they would.

Working on an article on ad hoc holds, I started questioning controllers about them. My goal was to pick up a good example but the comments I received talked about how they would be simple direct entries on course because controllers don't the unnecessary complexity of custom holding instructions any more than pilots do. I don't think they would react any more positively to creating ad hoc arcs using techniques they may have sitting gathering dust.

Plus, in order for ATC to assign a non-published arc in a random piece of airspace, wouldn't you have to be above have to be above their MVA where there are so many better ATC choices?
 
Pinecone said:
You could do it using the GPS as the DME and using the VOR to do the classic turn 10 degrees, fly 10 degrees, twist 10 degrees.
Click to expand...

I hated that method, which is why I think the watch your distance and turn adjust as necessary is better, less mechanical I guess.
 
RussR said:
Is this an academic question, or were you really issued such a clearance?

If this is the routing contained in a SID, you should be able to just load it from the database. Otherwise, yuck. Say to ATC, "are you kidding me? This is 2022."

But I'm not aware of a way to "build it" in the GTN750. If I had to, I'd just fly it in OBS mode I guess. No need to use the actual VOR signal, but I'd at least fake it. Although on second thought, using the actual VOR might be easier.
Click to expand...
While we’re here, there is a minimum distance from station for DME Arcs. Do you know it offhand?
 
midlifeflyer said:
That's why I added that I can't imagine they would.

Working on an article on ad hoc holds, I started questioning controllers about them. My goal was to pick up a good example but the comments I received talked about how they would be simple direct entries on course because controllers don't the unnecessary complexity of custom holding instructions any more than pilots do. I don't think they would react any more positively to creating ad hoc arcs using techniques they may have sitting gathering dust.

Plus, in order for ATC to assign a non-published arc in a random piece of airspace, wouldn't you have to be above have to be above their MVA where there are so many better ATC choices?
Click to expand...
They would have to comply with their rules on Minimum Altitudes. There are some that are below MVA. If there was a Diverse Vector Area, they could maybe apply that.
 
midlifeflyer said:
I haven't seen that. Got some US examples?
Click to expand...
Lots of airforce bases don't have an RNAV, after looking it looks like most of the VOR approach only airports are now "VOR/GPS" which I'm assuming is the same old VOR approach but they have added GPS to the name lol.
So color me wrong-ish :D
 
Justin Brady said:
Lots of airforce bases don't have an RNAV, after looking it looks like most of the VOR approach only airports are now "VOR/GPS" which I'm assuming is the same old VOR approach but they have added GPS to the name lol.
So color me wrong-ish :D
Click to expand...
Actually, the "VOR OR GPS" is old hat. VOR approach with GPS overlay. Goes back to the early 1990s. I think the program to create them ended about 10 years ago. There are just over 40 of those left, with a few typically slated for cancellation each year.
 
luvflyin said:
I was thinking ATC can issue impromptu DME Arcs. I know there was a time when they could. But I can’t find it anywhere in the current 7110.65.
Click to expand...

About 7 years ago I got one going into Grand Cayman. Arriving from the north we got instructions in intercept the 20nm arc and track it west until intersecting final, landing east. They did not have radar, so we also had to report passing a few radials. It has been a while since then so I could be wrong about the distance, but it was not the distance charted. We had no problem doing it old school.
 
midlifeflyer said:
Actually, the "VOR OR GPS" is old hat. VOR approach with GPS overlay. Goes back to the early 1990s. I think the program to create them ended about 10 years ago. There are just over 40 of those left, with a few typically slated for cancellation each year.
Click to expand...
I suppose I'm behind :D
That was my point though, it's just a VOR approach with a GPS overlay so what's the issue with using GPS as primary?
 
luvflyin said:
While we’re here, there is a minimum distance from station for DME Arcs. Do you know it offhand?
Click to expand...

7nm. 8260.3E para 2-4-3. You really don't see them that small very often, but one example is the HUT VOR RWY 4:

upload_2022-10-5_13-50-35.png
 
midlifeflyer said:
Actually, the "VOR OR GPS" is old hat. VOR approach with GPS overlay. Goes back to the early 1990s. I think the program to create them ended about 10 years ago.
Click to expand...

A little longer than that my friend! Closer to 20 if my memory serves correctly.
 
midlifeflyer said:
Plus, in order for ATC to assign a non-published arc in a random piece of airspace, wouldn't you have to be above have to be above their MVA where there are so many better ATC choices?
Click to expand...

I'm pretty sure that's true, so yes, why would they want to go through all the wording and instructions to get them on the arc (including back-and-forth as the pilot undoubtedly isn't prepared to copy and understand a clearance quite like this the first time), when they could just say "fly heading XXX".

And in the OP's case, that wouldn't be a legitimate departure clearance anyway. ATC can't just roll-their-own routing on departures until the airplane is above the MVA. (There is a caveat involving Diverse Vector Areas, but that doesn't apply here because the routing is not vectors.) And once the airplane is above the MVA, then my first paragraph applies.
 
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Justin Brady said:
It's because most people are more familiar/comfortable with their GPS than they are VOR.
There are still airports that have VOR approaches only, I'd prefer to fly those via the GPS than use the actual VOR personally (as I assume most people would)
Click to expand...

midlifeflyer said:
I haven't seen that. Got some US examples?
Click to expand...

There are a few. I'll hunt around. One related and quite prominent case is Van Nuys, VNY, which has 2 ILSes, an LDA, and 2 VORs, but no, zero, RNAV approaches. Doesn't exactly fit the case because why would you fly the VORs if the ILS or LDA was available (depending on direction), but is an interesting case in lack-of-RNAV anyway.

Plus there are ATC reasons potentially. As an illustrative example (not necessarily a real example as I don't know if this happens there or not), nearby VNY is WHP. WHP has an RNAV from the NW and a VOR-A from the southwest. No other approaches. If you're coming from the south, or ATC traffic demands it, maybe you fly the VOR-A.

Or any situation where the VOR approach end up being more convenient. This would typically be true if the RNAVs are all straight-in but the VOR is a circling approach that comes in from the side, and that's the side you're coming from. Weather permitting, flying it could save you 10 or more miles. FAM is a perfect example of this.

I also know of some airports (can't find one right now) that have an RNAV to one runway but not to the other end. The other end has a VOR. So if you want to fly straight-in to that runway, you're flying the VOR.
 
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luvflyin said:
I was thinking ATC can issue impromptu DME Arcs. I know there was a time when they could. But I can’t find it anywhere in the current 7110.65.
Click to expand...

I was issued an unpublished arc, by request, a few weeks ago.
 
Plano Pilot said:
About 7 years ago I got one going into Grand Cayman. Arriving from the north we got instructions in intercept the 20nm arc and track it west until intersecting final, landing east. They did not have radar, so we also had to report passing a few radials. It has been a while since then so I could be wrong about the distance, but it was not the distance charted. We had no problem doing it old school.
Click to expand...
I dunno what other Countries rules are.
 
RussR said:
Or any situation where the VOR approach end up being more convenient. This would typically be true if the RNAVs are all straight-in but the VOR is a circling approach that comes in from the side, and that's the side you're coming from. Weather permitting, flying it could save you 10 or more miles. FAM is a perfect example of this.
Click to expand...
There's one near me like that. I was thinking of it when I wrote my post. It's a VOR-A that puts you on downwind for one of the runways.
 
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