GNS430 on the Airway

So how far off an airway is an aircraft when they are following a GPS flight
plan with every intersection and VOR? Is there an article or study somewhere
that includes metrics to back it up? For example, "a non-WAAS GPS-derived
line direct btween two intersection xx miles away will differ from the
airway between those same two intersections by x.x statute miles." How do
the error allowances play into this?

Marco

"nooneimportant" wrote in message
news:gPgGf.57025$V.55301@fed1read04...
But the workaround is very easy... if V123 goes throug the abc bca and cab
VOR's then you creat the flight plan wiht waypoints at each vor or
intersection on the route. If you are off airway and choose to fly TO the
airway, simply go to the FPL screen, select teh NEXT fix on the plan and
activate the leg. Your CDI will be in relation to that leg, not a direct
line to the fix.

Tho i do wish you could simply put AIRPORTA D- abcVOR-V123-cabVORD D-
AIRPORTB. But it only saves a few entries on most flights. And in reality
I've NEVER gotten what i was cleared for IFR wise when i filed /G.... I
MIGHT get to the second fix, then its "Proceed Direct AIRPORTB" or
something
similar that cuts off about 20 minutes of flying time.




"Robert M. Gary" wrote in message
oups.com...
That's one major limitation of the Garmin products. Not having airways
is very, very irritating especially to those of us that fly in high
traffic areas (such as L.A.). When an approach controller machine guns
you with a new 6 airway route without giving you any intersections it
leaves you jumping for your chart. When I had my king unit, I would
just put the pink airplane line on top of the blue airway line and I
was done. I hope Garmin addresses this someday.

-Robert








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So how far off an airway is an aircraft when they are following a GPS flight
plan with every intersection and VOR?

If you miss entering one of the bends in the airway it could be 20 or
30 miles off. The point is that you are now back to the 1970's,
grabbing your enroute chart and trying to figure out all the airway
bends when you could have a 1990's handheld GPS (King Skymap IIIC) and
it would do it all for you.

-Robert

"Marco Leon" mmleon(at)yahoo.com wrote:

So how far off an airway is an aircraft when they are following a GPS flight
plan with every intersection and VOR? Is there an article or study somewhere
that includes metrics to back it up? For example, "a non-WAAS GPS-derived
line direct btween two intersection xx miles away will differ from the
airway between those same two intersections by x.x statute miles." How do
the error allowances play into this?


Since unaugmented GPS (not using WAAS) is accurate to 10 meters or so
(plus/minus) and an airway is plus/minus four MILES (or is is two?)
the navigation source (GPS) is not a major error source.

Ron Lee

On 02/09/06 08:09, Ron Lee wrote:
"Marco Leon" mmleon(at)yahoo.com wrote:

So how far off an airway is an aircraft when they are following a GPS flight
plan with every intersection and VOR? Is there an article or study somewhere
that includes metrics to back it up? For example, "a non-WAAS GPS-derived
line direct btween two intersection xx miles away will differ from the
airway between those same two intersections by x.x statute miles." How do
the error allowances play into this?


Since unaugmented GPS (not using WAAS) is accurate to 10 meters or so
(plus/minus) and an airway is plus/minus four MILES (or is is two?)
the navigation source (GPS) is not a major error source.

An airway is 8 miles wide (4 miles on either side of the centerline).

One of the problems is that GPS accounts for magnetic variations differently
than the VORs do. Also I don't think GPS accounts for the fact that the
VOR radial are not exactly aligned with magnetic north (what is this called?
variance? I can't remember - it's documented in the A/FD).

GPS position errors would be on top of all this.


Ron Lee


--
Mark Hansen, PP-ASEL, Instrument Airplane
Cal Aggie Flying Farmers
Sacramento, CA

Mark Hansen wrote:


One of the problems is that GPS accounts for magnetic variations
differently
than the VORs do. Also I don't think GPS accounts for the fact that the
VOR radial are not exactly aligned with magnetic north (what is this
called?
variance? I can't remember - it's documented in the A/FD).

This would have an effect only if the procedure has you tracking a defined VOR
radial. There might be some such procedures, but I can't think of any at the moment.

All the airway segments (that's what we're talking about, right?) that I know of
have a defined point at each end of the segment. There is one and only one great
circle route between those two points. It's the same great circle whether you
follow it with a GPS or a VOR receiver.

Dave

Dave Butler wrote:

Mark Hansen wrote:


All the airway segments (that's what we're talking about, right?) that I
know of have a defined point at each end of the segment. There is one
and only one great circle route between those two points. It's the same
great circle whether you follow it with a GPS or a VOR receiver.

The charted airway mag bearing is the issue. It was developed from one
source and Garmin, et al, may or may not use the same source.

But, you're right, it's no big deal, unless the airway has an
intersection course change of some magnitude.

The issues with mag var and declination are easily absorbed by the huge
widths of the victor airway. The problem is airway course changes
between facilities. An autoload of the airway not only solves that
issue, it keeps everything "spot on" and has all the non-compulsory
reporting points loaded and ready, if needed.

Ron Lee wrote:

"Marco Leon" mmleon(at)yahoo.com wrote:


So how far off an airway is an aircraft when they are following a GPS flight
plan with every intersection and VOR? Is there an article or study somewhere
that includes metrics to back it up? For example, "a non-WAAS GPS-derived
line direct btween two intersection xx miles away will differ from the
airway between those same two intersections by x.x statute miles." How do
the error allowances play into this?



Since unaugmented GPS (not using WAAS) is accurate to 10 meters or so
(plus/minus) and an airway is plus/minus four MILES (or is is two?)
the navigation source (GPS) is not a major error source.

Ron Lee

VOR airway's primary is plus/minues 4 to 51 miles, where it expands at
4.5 degrees. The secondary is an additional 2 miles, which expands at
6.7 degrees at 51 miles.