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

Jim Harper wrote:

wrote in message ...



As a previous poster posted, you are in a non-radar environment when
you hear "radar contact lost". You are also in a non-radar environment
when you see mandatory reporting points. I believe that this mostly
applies to the great wide West.

When flying at, or near MEA in the great wide West there are lots of radar holes where ATC doesn't bother to terminate
radar because you will reappear in 10 or 15 minutes. So, they say nothing.

As to the remainder of your concern TCAS has gone a long ways to solving the en route problem of midair potential for
airliners and biz jets. That is the real solution for everyone. It should be a higher priority for light aircraft.

"Peter Duniho" wrote in message
...
"Icebound" wrote in message
...
But in the GPS case, it is pretty much in "every" case that two aircraft
using those two waypoints will be pretty much in the center.

But "pretty much" still covers quite a bit of ground. There is only an
increased risk of a collision, not a virtual certainty.


Oh, for sure.

"Icebound" wrote in message ...
"SelwayKid" wrote in message
om...
"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).

...snip...

As for being difficult to fly the VOR, it was/is no more difficult
than flying a compass heading and holding it.....which many pilots
seem unable to do anymore. They would prefer that electronic gadgets
do their flying for them and no thoughts as to what happens when the
electrodes take a vacation.


Never having flown a VOR course myself... I still doubt very much that any
two pilots (OR auto-pilots), flying reciprocal headings between two VORs,
would both be able to *simultaneously* hold a course to within 10 feet of
the centre-line for the whole course, considering the receiver errors and
that the VOR radial-signal *itself* probably varies more than that.

I could be wrong.
*********************
Icebound
If you have never flown a VOR course, where in hell do you fly? And,
if you have never flown a VOR course, what do you know about them or
what their capabilities are? Part of the PTS for every US rating
involves VOR.
Beyond that, let me ask if you are a licensed pilot? Hmmm, well you
may be in another country, perhaps 3rd world without VOR but even
then, of the 26 countries I've worked in, all had VOR coverage of some
kind. So again, where do you fly?
Ol Shy & Bashful

Your exactly right and the use of parallel track will help that. Offset to
the right a
bit.


"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???

"Gene Whitt" wrote in message hlink.net...
Y'All,
This entire thread seems to be totally entranced with the possible conflict
of aircraft on a heading/course. Whereas, the most likely conflict is in
altitude between IFR and VFR supposedly flying with 500 feet of FAA
separation.

Some time ago I was told that ATC figures a + - error 300 feet.
The altimeter is likewise allowed a 75 foot + - error. Not knowing for
certain but assuming it is so. Look at the following senario.

If we have an IFR and a VFR fllying in opposite hemisphereic directions in
VFR conditions we have several possible extreme conditions. Take the first
aircraft indicating 6000 feet west bound. The second aircraft indicating
5500 feet east bound. If both the transponders and altimeters have errors
to the extreme in the opposite directions, they could still miss each other.

If the first aircraft is flying 250 lower than indicated due to accumulated
instrment error, while the other is actually flying 250 feet higher than
indicated we have only see and be seen to save the situation.

To me the probability of a midair is more likely to altitude error than
heading error. The odds of having two such aircraft with hemispheric
accumulative opposite errors in altitude sufficient to cause a midair is
unlikely but more likely than an opposite heading midair. I believe this
because the distances are matters of feet rather than miles. It takes both
to actually cause the midair.so the total emphasis on course/heading is only
a part of the equation.

I haven't even mentioned GPS altitude as a factor.
Mud wrestling anyone?

Gene

Excellent point Gene. This is why maintaining a good visual scan is
important, and why TCAS and TCAD systems are so valuable. I wish that
we were at the point where every airplane equipped with a transponder
also had a TCAS or TCAD system installed. It would be nice if this
equipment were affordable enough to do this.

Dean

"SelwayKid" wrote in message
om...
"Icebound" wrote in message
...
"SelwayKid" wrote in message
om...
"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).

...snip...

As for being difficult to fly the VOR, it was/is no more difficult
than flying a compass heading and holding it.....which many pilots
seem unable to do anymore. They would prefer that electronic gadgets
do their flying for them and no thoughts as to what happens when the
electrodes take a vacation.


Never having flown a VOR course myself... ...snip...

I could be wrong.



*********************
Icebound
If you have never flown a VOR course, where in hell do you fly? .... So
again, where do you fly?

Hey, I never said that I flew at all. yet. I don't think that disqualifies
me from trying to clarify some stuff for the day that I might :-)

Inspire me. Educate me. Convince me that a VOR course can be held to the
same 10 metre tolerance over 100 NM miles, that it appears a GPS course can.
(Without the GPS in the cockpit for reference, of course.)

If you have never flown a VOR course, where in hell do you fly?

I am a certificated American pilot, and have been for six years. I
have never flown a VOR course and never expect to. I fly in New
Hampshire, Maine, and Massachusetts. I have about 350 hours.

(Early on, I owned a Sporty's handheld with nav feature. I once tuned
it to the Pease VOR just to see how it worked, and never used the
feature again. After not very long, I got rid of the Sporty's for a
Yaseu/Vertex without the nav feature, and have never regretted it. If
I need an electronic aid, I use the GPS. Indeed, if it's comfortable
to do so, I avoid VORs on the theory that they must be airplane
magnets. To a lesser extent, the same must be true of VOR courses,
depending on one's distance from the VOR. Who needs places where other
airplanes congregate?)


all the best -- Dan Ford
email: (put Cubdriver in subject line)

Warbird's Forum www.warbirdforum.com
Piper Cub Forum www.pipercubforum.com
the blog www.danford.net

Bill Denton wrote:

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?


Presumably, they would both offset to the right, and I think the greatest
concern is about opposite direction traffic.

Cub Driver ) wrote:

I am a certificated American pilot, and have been for six years. I
have never flown a VOR course and never expect to. I fly in New
Hampshire, Maine, and Massachusetts. I have about 350 hours.

Is this VFR or IFR?

I mainly file and fly IFR in the Northeast US and I have learned that if
I am flying to or from Boston or anywhere near NYC, I must file and at
least start flying airways. The controllers will offer direct where
possible, but the volume of traffic during the peak hours often prevents
this.

In my experience, there have been a few times where the only way I could
get off the airways was to cancel IFR, weather depending.

--
Peter

Peter Duniho ) wrote:
: GPS increases the chances of collision, by reducing the average error. But
: the issue did already exist with VOR navigation. Keep in mind that GPS
: error is still going to be on the order 10 to 30 meters or so, just from the
: position information standpoint, and then on top of that you still have the
: problem of the airplane being kept exactly at the intended position (even
: with an autopilot, there's going to be some slop, and not all pilots are
: using autopilots in conjunction with their GPS navigation).

The GPS error you have quoted is relative to a fixed point on the ground.
Most modern cheap GPS recievers in the same region looking at the same
sats with differential corrections are within meters of each other
and with good processing can produce a relative position within a few
inches.

The way to deal with this is to simply move the GPS course .1 nmi
to the right. This means if your doing a 90 degree turn over a VOR
using a GPS, you should make your turn .14 nmi away from the VOR
and you should be able to see it out the left window.

At this point it won't matter much considering the GA autopilot slop
but things could change in the future and now is a good time to
start putting these things in place.

but there are more an more aircraft flying in the skys that don't
but things could change in the future and now is a good time to
start putting these things in place.

-tim
http://web.abnormal.com