Parallel Track function in GPS?

[Roy Smith]

Yesterday I played with the parallel track function in the CNX-80 for
the first time. I was introducing the CNX-80 to a student and I had
planned a VFR flight via airways. My student (rightfully) questioned
the wisdom of an over-water segment, so we decided to fly that segment
on a 5-mile offset parallel track (it got us over land and was a good
excuse to explore a software function I'd never used before).

But, here's my question. Why is it in the box to begin with? Other
than the gee-wiz marketing value, is there any real practical reason for
it existing?

VFR, we didn't need it (it was easy enough to follow the coastline
visually). IFR, it would have put us outside the airway boundary, so
it's probably not very useful there either. Is "fly parallel to V157
offset 2 miles to the left" something that I might ever expect to get in
an IFR clearance if I file /G ?

[Barry]

> Is "fly parallel to V157 offset 2 miles to the left" something
> that I might ever expect to get in an IFR clearance if I file /G ?

One of the concerns with GPS is that the great accuracy can sometimes increase
the probability of a midair collision compared to conventional nav. Consider
two aircraft traveling on the same route in opposite directions at different
altitudes, in non-radar airspace. If, due to a pilot or controller error,
both planes end up at the same altitude, the probability that they would hit
was quite small with VOR, but much higher with GPS. Some airline pilots have
already started flying lateral offsets on their own, and ICAO is studying the
issue and trying to come up with standards. One of the proposed criteria is
that the procedure be transparent to the controllers. So it's unlikely that
ATC will ever assign a clearance to fly an offset, but at some point pilots
might be permitted or required to fly an offset on some routes.

[Judah]

Hi Roy,
I seem to recall the CNX-80 Tutorial talks about it being used for
weather avoidance during IFR enroute flight. I guess their thought is
that you can use it to request a diversion around weather, eg: a 5-mile
diversion to the left. Then you can program it into the CNX-80 and stay
parallel to your track.

As you know, I don't have a whole lot of IFR experience - I had thought
that you typically tell ATC about your diversions for weather in degrees
and time (5 degrees left for about 5 min), so it very well may be one of
those "sex-sells" types of features. But I thought I'd share with you
what I read on the tutorial...



Roy Smith > wrote in
:

> Yesterday I played with the parallel track function in the CNX-80 for
> the first time. I was introducing the CNX-80 to a student and I had
> planned a VFR flight via airways. My student (rightfully) questioned
> the wisdom of an over-water segment, so we decided to fly that segment
> on a 5-mile offset parallel track (it got us over land and was a good
> excuse to explore a software function I'd never used before).
>
> But, here's my question. Why is it in the box to begin with? Other
> than the gee-wiz marketing value, is there any real practical reason
> for it existing?
>
> VFR, we didn't need it (it was easy enough to follow the coastline
> visually). IFR, it would have put us outside the airway boundary, so
> it's probably not very useful there either. Is "fly parallel to V157
> offset 2 miles to the left" something that I might ever expect to get
> in an IFR clearance if I file /G ?

[Roy Smith]

In article >,
Judah > wrote:

> Hi Roy,
> I seem to recall the CNX-80 Tutorial talks about it being used for
> weather avoidance during IFR enroute flight. I guess their thought is
> that you can use it to request a diversion around weather, eg: a 5-mile
> diversion to the left. Then you can program it into the CNX-80 and stay
> parallel to your track.
>
> As you know, I don't have a whole lot of IFR experience - I had thought
> that you typically tell ATC about your diversions for weather in degrees
> and time (5 degrees left for about 5 min), so it very well may be one of
> those "sex-sells" types of features. But I thought I'd share with you
> what I read on the tutorial...

Hi Judah!

What you said sounds reasonable. Whenever I've wanted to alter course
for weather, I have indeed made my request/report in terms of heading,
but that's mostly because that's what's been the most convenient in the
pre-GPS days (if the only tool you've got is a hammer, everything looks
like a nail). I suppose now that I've got the tool, "I'd like to offset
5 miles left of course for weather" might work just as well.

[Ben Jackson]

In article >,
Judah > wrote:
> I seem to recall the CNX-80 Tutorial talks about it being used for
> weather avoidance during IFR enroute flight.

That's exactly what the manual for the old Apollo LORAN 604 says
regarding PTK on the LORAN. You'd think they could come up with a
second use for it by now!

As far as I know PTK for GPS just keeps those $900 annunciator/switch
makers in business.

--
Ben Jackson
>
http://www.ben.com/

[Tarver Engineering]

"Ben Jackson" > wrote in message
news:U1gjc.26305$cF6.1144747@attbi_s04...
> In article >,
> Judah > wrote:
> > I seem to recall the CNX-80 Tutorial talks about it being used for
> > weather avoidance during IFR enroute flight.
>
> That's exactly what the manual for the old Apollo LORAN 604 says
> regarding PTK on the LORAN. You'd think they could come up with a
> second use for it by now!
>
> As far as I know PTK for GPS just keeps those $900 annunciator/switch
> makers in business.

The big boys with their INS have it, why shouldn't you?

[kage]

If you are flying in RVSM airspace, like across the Atlantic in the "tracks"
and you have certain types of emergencies, ATC wants you to parallel the
course 30 miles off to the right. That's one reason.

Karl
>
> But, here's my question. Why is it in the box to begin with? Other
> than the gee-wiz marketing value, is there any real practical reason for
> it existing?

[Stan Gosnell]

Roy Smith > wrote in news:roy-
:

> Yesterday I played with the parallel track function in the CNX-80 for
> the first time. I was introducing the CNX-80 to a student and I had
> planned a VFR flight via airways. My student (rightfully) questioned
> the wisdom of an over-water segment, so we decided to fly that segment
> on a 5-mile offset parallel track (it got us over land and was a good
> excuse to explore a software function I'd never used before).
>
> But, here's my question. Why is it in the box to begin with? Other
> than the gee-wiz marketing value, is there any real practical reason for
> it existing?

We use it offshore for approaches. We can do a parallel-offset approach to
a rig, offsetting the final approach course 1/2 mile so that we aren't
flying directly at the rig on final. It's also useful for search and
rescue, and likely for other utility uses. Not everyone flies spam cans
between airports.

--
Regards,

Stan

[Roy Smith]

Stan Gosnell > wrote:
> We use it offshore for approaches. We can do a parallel-offset approach to
> a rig, offsetting the final approach course 1/2 mile so that we aren't
> flying directly at the rig on final.

Oddly enough, the CNX-80 only allows you integral mile offsets. AFAICT,
there's no way to do a 1/2 mile offset.

> It's also useful for search and
> rescue, and likely for other utility uses.

OK, I guess those all make sense.

> Not everyone flies spam cans between airports.

I'm not completely sure, sir, but I do believe I'm being made fun of :-)

[Stan Gosnell]

Roy Smith > wrote in
:

> Oddly enough, the CNX-80 only allows you integral mile offsets.
> AFAICT, there's no way to do a 1/2 mile offset.

Not a very useful implementation, then.
> I'm not completely sure, sir, but I do believe I'm being made fun of
> :-)
>
Only in good fun. ;-)

--
Regards,

Stan

[John R. Copeland]

"Roy Smith" > wrote in message =
...
>=20
> Oddly enough, the CNX-80 only allows you integral mile offsets. =
AFAICT,=20
> there's no way to do a 1/2 mile offset.
>=20

Do you HAVE to keep the needle centered?
---JRC---

[[email protected]]

Tarver Engineering wrote:

>
>
> The big boys with their INS have it, why shouldn't you?

And, it was never used, either.

[Stan Gosnell]

"John R. Copeland" > wrote in
:

> Do you HAVE to keep the needle centered?

To fly an offset Offshore Standard Approach Procedure, yes.

--
Regards,

Stan

[John R. Copeland]

"Stan Gosnell" > wrote in message =
...
> "John R. Copeland" > wrote in
> :=20
>=20
> > Do you HAVE to keep the needle centered?
>=20
> To fly an offset Offshore Standard Approach Procedure, yes.
>=20
> --=20
> Regards,
>=20
> Stan
>=20

Naturally, you are right about approach procedures, Stan.
(And that's exactly what you posted earlier about, too.)
I only had enroute legs in mind for using pointer offsets.
---JRC---

[Bob Noel]

In article >, Roy Smith
> wrote:

> Yesterday I played with the parallel track function in the CNX-80 for
> the first time. I was introducing the CNX-80 to a student and I had
> planned a VFR flight via airways. My student (rightfully) questioned
> the wisdom of an over-water segment, so we decided to fly that segment
> on a 5-mile offset parallel track (it got us over land and was a good
> excuse to explore a software function I'd never used before).
>
> But, here's my question. Why is it in the box to begin with? Other
> than the gee-wiz marketing value, is there any real practical reason for
> it existing?

from a co-worker involved in this kind of stuff:

Offset tracks allow aircraft to pass en route, avoid bad weather, and
increase airspace capacity by avoiding busy intersections.

--
Bob Noel

[[email protected]]

Bob Noel wrote:

> from a co-worker involved in this kind of stuff:
>
> Offset tracks allow aircraft to pass en route, avoid bad weather, and
> increase airspace capacity by avoiding busy intersections.

Could you provide examples of where this is used?

[Bob Noel]

In article >, wrote:

> > from a co-worker involved in this kind of stuff:
> >
> > Offset tracks allow aircraft to pass en route, avoid bad weather, and
> > increase airspace capacity by avoiding busy intersections.
>
> Could you provide examples of where this is used?

Not much use yet, other than oceanic routes, I guess. But the theory
is that it will be used in RNP airspace.

--
Bob Noel

[[email protected]]

Bob Noel wrote:

>
> Not much use yet, other than oceanic routes, I guess. But the theory
> is that it will be used in RNP airspace.
>
> --
> Bob Noel

That is a major disconnect between avionics engineers who dream of selling
more and more equipment and of an ATC system driven by radar separation and
navigation. And, the radar isn't getting any better with some limited
terminal exceptions.

[Bob Noel]

In article >, wrote:

> > Not much use yet, other than oceanic routes, I guess. But the theory
> > is that it will be used in RNP airspace.
>
> That is a major disconnect between avionics engineers who dream of
> selling
> more and more equipment and of an ATC system driven by radar separation
> and
> navigation. And, the radar isn't getting any better with some limited
> terminal exceptions.

The move to RNP is, in part, driven by the desire for increased
airspace capacity, including airspace with limited radar coverage.

--
Bob Noel

[[email protected]]

Bob Noel wrote:

>
>
> The move to RNP is, in part, driven by the desire for increased
> airspace capacity, including airspace with limited radar coverage.
>

No doubt about its usefulness in areas with limited, or no, radar coverage.
But, I doubt that offset tracks would do much good there. Where the terrain
environment would permit parallel tracks, the publication of parallel tracks
as separate database routes would probably be much safer than issuing
parallel tracks in a non-radar environment.

[[email protected]]

>

Final sentence should read:

than issuing parallel *offset* tracks in a non-radar environment.

[Barry]

> No doubt about its usefulness in areas with limited, or no, radar coverage.
> But, I doubt that offset tracks would do much good there. Where the terrain
> environment would permit parallel tracks, the publication of parallel tracks
> as separate database routes would probably be much safer than issuing
> parallel offset tracks in a non-radar environment.

The push for lateral offsets is greatest for non-radar environments, where
controllers are less likely to catch an operational error that puts two planes
on the same track and altitude. As I stated in an earlier post, one of the
proposed criteria is that the use of lateral offsets be transparent to the
controller. So offsets will probably be implemented as procedural changes
(for example, always fly 1 NM to the right of centerline if able), not as
clearances.

[[email protected]]

Barry wrote:

> > No doubt about its usefulness in areas with limited, or no, radar coverage.
> > But, I doubt that offset tracks would do much good there. Where the terrain
> > environment would permit parallel tracks, the publication of parallel tracks
> > as separate database routes would probably be much safer than issuing
> > parallel offset tracks in a non-radar environment.

I doubt the industry will buy into that. Too many opportunities for errors.
Plus, the parallel track has to have the same obstacle assessment as the "primary"
track, so it would be better to have them published and in the database; i.e.,
Track Bishop Alpha, Track Bishop Bravo, etc.

[Tarver Engineering]

> wrote in message ...
>
>
> Bob Noel wrote:
>
> >
> > Not much use yet, other than oceanic routes, I guess. But the theory
> > is that it will be used in RNP airspace.

> That is a major disconnect between avionics engineers who dream of selling
> more and more equipment and of an ATC system driven by radar separation
and
> navigation. And, the radar isn't getting any better with some limited
> terminal exceptions.

The Greens won't let us pour concrete, so what is the alternative?
1) restrict small GA access
2) ...

[tscottme]

Barry > wrote in message
...
> > Is "fly parallel to V157 offset 2 miles to the left" something
> > that I might ever expect to get in an IFR clearance if I file /G ?
>
> One of the concerns with GPS is that the great accuracy can sometimes
increase
> the probability of a midair collision compared to conventional nav.
Consider
> two aircraft traveling on the same route in opposite directions at
different
> altitudes, in non-radar airspace. If, due to a pilot or controller
error,
> both planes end up at the same altitude, the probability that they
would hit
> was quite small with VOR, but much higher with GPS. Some airline
pilots have
> already started flying lateral offsets on their own, and ICAO is
studying the
> issue and trying to come up with standards. One of the proposed
criteria is
> that the procedure be transparent to the controllers. So it's
unlikely that
> ATC will ever assign a clearance to fly an offset, but at some point
pilots
> might be permitted or required to fly an offset on some routes.
>

This FMS/GPS-assisted mid-air risk is what I have seen discussed in
numerous big-iron forums and an ALPA magazine. In both places the
discussion seemed to favor a small offset, say 1 mile right of
centerline, to avoid nose to nose meetings.

--
Scott

[[email protected]]

Roy Smith > wrote:
> Yesterday I played with the parallel track function in the CNX-80 for
> But, here's my question. Why is it in the box to begin with? Other
> than the gee-wiz marketing value, is there any real practical reason for
> it existing?

We use it for search and rescue in Civil Air Patrol. Not only is
there parallel track in some of the boxes, some of the Garmins have
the ability to turn on the CAP grid system "overlay", so that one can
see (within the accuracy of GPS) that you are inside or outside of a
particular grid, and turning on the "bread crumbs", you can even see
how accurately you flew the grid and if you covered it all.

Best regards,

LtCol Jer/ Eberhard, Colorado Wing Checkpilot (airplanes and gliders)

--
LtCol Jer/ Eberhard, CO-Wing, Thompson Valley CS., Ft Collins, CO
CELL/VM: 970 231-6325, CELL Message: 9702316325'at'mobile.att.net
EMAIL: jer'at'frii.com WEB: http://www.frii.net/~jer
C-206 N9513G, CFII Airplane&Glider, FAA-DEN Aviation Safety Counselor
CAP-CO Mission&Aircraft CheckPilot, BM218 HAM N0FZD, 197 Young Eagles!