Can GPS be *too* accurate? Do I need some XTE??

"John R. Copeland" wrote:

"Icebound" wrote in message ...


The remainder of the article describes the 1-nm or 2-nm offsets allowed,
and only to the right of centerline, with effective date of June 10, 2004.

The name of this concept is "Strategic Lateral Offset Procedure",
so everyone can understand they've now added SLOP to the route system!
As Dave Barry might say, I am not making this up.
---JRC---

Keep in mind those offsets are in oceanic airspace where the route width is 25 or 30 miles, centerline to
edge. Along a domestic airway, offsets of those magnitude would be far too large. An offset of 1/10 of a
mile would probably be effective without creating an issue with compliance with FAR 91.189. (although the feds
might not buy that rationale ;-)

If the weather is IMC you are well advised to remain on centerline. If it is
VMC, and your equipment will support parallel track offset, then 1/10 of a mile
is probably going to mitigate your concerns. But, if operating IFR it is
essential to terminate offset operations before beginning an instrument approach
procedure.

If your equipment won't support parallel offset, then your only remaining option
is to fly the autopilot in heading mode and try to keep the XTRK error at some
value approximating 1/10 of a n.m.

Icebound wrote:

In the "good old" VOR days, it must have been pretty difficult to fly down
the centerline of an airway (or of any direct track).

So an eastbound VFR/IFR aircraft descending from 7500/7000 to his
destination, was more than likely to avoid traffic... on the reciprocal
track passing him by at 6500 or 6000... by some significant horizontal
error-distance, even if they didn't see each other (big sky theory :-) ).

GPS horizontal accuracy with WAAS is already in the order of magnitude of a
Cessna's wingspan, and some are talking about getting it down to mere
inches.

So the question is: If my Westbound Cessna at 6000 feet (with the autopilot
keeping it happily on the GPS-track centerline) meets the descending Bonanza
on the reciprocal track between the same two airports (using a similar
GPS/a-p combo), there is a distinct possibility that the horizontal
clearance may be zero...

...so is there anything in the current crop of GPS and/or Autopilot systems
that allow me to maintain a small cross-track error of my choosing, without
actually entering off-navaid-off-airport waypoints? ...or do we care; am I
overly concerned???

Stan Gosnell wrote:

The Trimble 2102 has it, and so do most other units.


Do you know whether the Garmin 400/500 series (other than the 480) have it?

"Icebound" wrote in message ...
So the question is: If my Westbound Cessna at 6000 feet (with the autopilot
keeping it happily on the GPS-track centerline) meets the descending Bonanza
on the reciprocal track between the same two airports (using a similar
GPS/a-p combo), there is a distinct possibility that the horizontal
clearance may be zero...

...so is there anything in the current crop of GPS and/or Autopilot systems
that allow me to maintain a small cross-track error of my choosing, without
actually entering off-navaid-off-airport waypoints? ...or do we care; am I
overly concerned???

As others have pointed out, the GNS 480/CNX 80 does allow a
cross-track error. I did want to make one small philosophical
point...here in the deep south, we generally get direct routing. If
you have the capability, and you ask for the direct routing, you
generally are increasing your safety (by an admittedly tiny amount).
Further, anyone who is flying VFR and uses the airways is also
increasing his/her risk by that same small amount.

I do doubt that ATC will descend you through another aircraft on the
same airway, so the chances of meeting an IFR aircraft is
diminishingly small, but your concern is most likely regarding the VFR
aircraft sharing the airway.

Hence this discussion is of the "how many angels can dance on the head
of a pin" sort...making it perfect for USENET. And the take-home
points are(IMO) fly direct whenever allowed. Generate your courseline
from some NON-standard point. That is, don't go direct from some
intersection or from the runway...go from some offset point...avoiding
the other guy (most likely VFR) doing the same thing from your
destination. Don't use airways unless you must. And when you fly the
Atlantic (in a non-radar environment)...or the non-radar environments
of the USA...use SLOP!

Jim

Jim Harper wrote:

. And when you fly the
Atlantic (in a non-radar environment)...or the non-radar environments
of the USA...use SLOP!


SLOP is approved for oceanic. Do you know if it is approved for non-radar environments of the USA? If so, what
are the numbers to use? How do I determine when I am in a non-radar environment in the USA?

wrote:

How do I determine when I am in a non-radar environment in the USA?

When you hear "radar contact lost" or when you don't hear "radar contact".

[how and whether to fly an offset on a GPS track]

Just hand fly. You can hand fly any offset you like.

Jose
--
Freedom. It seemed like a good idea at the time.
for Email, make the obvious change in the address.

I noticed the later posts referenced a set of "rules" for setting up the
"error", but absent those, you are back to the same old game of chance.
What's to prevent another pilot from picking a corresponding "error" that
would still maintain the head-on courses?

And I don't know if this is a trick question, but if you are at 6000 (no
+500) wouldn't you be on an IFR flight plan, talking to ATC, and receiving
traffic advisories?





"Icebound" wrote in message
...
In the "good old" VOR days, it must have been pretty difficult to fly down
the centerline of an airway (or of any direct track).

So an eastbound VFR/IFR aircraft descending from 7500/7000 to his
destination, was more than likely to avoid traffic... on the reciprocal
track passing him by at 6500 or 6000... by some significant horizontal
error-distance, even if they didn't see each other (big sky theory :-) ).

GPS horizontal accuracy with WAAS is already in the order of magnitude of
a
Cessna's wingspan, and some are talking about getting it down to mere
inches.

So the question is: If my Westbound Cessna at 6000 feet (with the
autopilot
keeping it happily on the GPS-track centerline) meets the descending
Bonanza
on the reciprocal track between the same two airports (using a similar
GPS/a-p combo), there is a distinct possibility that the horizontal
clearance may be zero...

...so is there anything in the current crop of GPS and/or Autopilot
systems
that allow me to maintain a small cross-track error of my choosing,
without
actually entering off-navaid-off-airport waypoints? ...or do we care; am I
overly concerned???

Bill Denton ) wrote:

And I don't know if this is a trick question, but if you are at 6000 (no
+500) wouldn't you be on an IFR flight plan, talking to ATC, and receiving
traffic advisories?

In the US and outside of class B airspace, it is the pilot, not ATC, who
is ultimately responsible for IFR/VFR traffic separation. A VFR traffic
advisory to an IFR aircraft is a courtesy offered by ATC; it is not a
guarantee.

--
Peter

"Peter R." wrote in message
...
Bill Denton ) wrote:

And I don't know if this is a trick question, but if you are at 6000 (no
+500) wouldn't you be on an IFR flight plan, talking to ATC, and
receiving
traffic advisories?

In the US and outside of class B airspace, it is the pilot, not ATC, who
is ultimately responsible for IFR/VFR traffic separation. A VFR traffic
advisory to an IFR aircraft is a courtesy offered by ATC; it is not a
guarantee.

--
Peter

You might want to rethink your reply.

A pilot in clouds or other IMC cannot provide separation to any traffic he
cannot see.