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Parallel Track function in GPS?



 
 
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  #1  
Old April 26th 04, 07:15 PM
Roy Smith
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Default Parallel Track function in GPS?

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 ?
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  #2  
Old April 26th 04, 07:41 PM
Barry
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Default

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.



  #3  
Old April 26th 04, 07:57 PM
Judah
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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 ?


  #4  
Old April 26th 04, 08:10 PM
Roy Smith
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Default

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.
  #5  
Old April 26th 04, 11:28 PM
Ben Jackson
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Default

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/
  #6  
Old April 27th 04, 01:13 AM
Tarver Engineering
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Default


"Ben Jackson" wrote in message
news:[email protected]_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?


  #7  
Old April 27th 04, 01:42 AM
kage
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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?



  #9  
Old April 27th 04, 02:39 AM
Roy Smith
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Default

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 :-)
  #10  
Old April 27th 04, 02:51 AM
Stan Gosnell
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Default

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

 




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