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

This thread has gotten so long, I including my original reply to ensure that
we are on the same page:

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?

My comments are in the text...4


"Peter Duniho" wrote in message
...
"Bill Denton" wrote in message
...
The question mark "implied" nothing; it directly indicated that I was
asking
a question.

Fine. As hard as it is to imagine, let's grant your claim regarding the
lack of an implication. Then the answer to your question is "yes,
assuming
you're also above 3000' AGL, but so what?" Emphasis on "so what?"

Given that there was no implication intended, what in the world was the
point of your original reply?

And if the conditions in my question were "true", you would not need to
fly
an offset on a GPS course, despite GPS improved accuracy, any more than
you
would need to fly an offset on a VOR course; traffic avoidance would be
handled by ATC.

In other words, you WOULD "need" to fly an offset, in order to ensure no
conflict with other traffic. There is a very real risk of a collision
when
flying an airway, whether you're using GPS or VOR navigation. In
practice,
we as pilots generally choose looking out the window over offsetting our
course, but the "need" is there nevertheless.

As you will note from my original reply, the point was that if everyone is
randomly choosing their own offset, you aren't really improving your odds of
avoiding a head-on very much. You would probably be better off just flying
the centerline; at least you would know where to look for other traffic.



You continue to claim (just as your first post implied) that ATC handles
traffic avoidance for IFR flights, but that's simply not true. ATC only
separates IFR flights from other IFR flights (except in particular kinds
of
airspace where VFR flights are also given traffic separation...a very
small
portion of the national airspace system).

Aircraft operate under the same traffic principles as automobiles: There is
a set of rules. If everyone follows the rules, no problem. But is someone
breaks the rules, you have a strong potential for a problem.

If you are IFR in IMC you probably will not be able to use "see and avoid".
You simply cannot see through the clouds/rain/whatever. You have to look to
ATC for separation, which they will provide for all aircraft on IFR flight
plans. Aircraft flying under VFR are not supposed to be in IMC. If they are,
that's a violation of the rules. And VFR and IFR aircraft are supposed to
maintain a 500 foot vertical separtaion above 3000 feet AGL. If the
separtion is not maintained, that's a violation of the rules. And when you
have a violation of the rules, the accident risk increases.

FAR 91.113 (c) mandates that when weather condtions permit, all aircraft,
whether flying VFR or IFR, must observe "see and avoid".

To sum it up, if you are IFR in IMC, you have to rely on ATC to separate you
from other IFR traffic; there should not be any VFR traffic there. If you
are in VMC, whether VFR or IFR, you must observe "see and avoid". And all
aircraft must maintain the 500 foot separation between VFR and IFR aircraft.

Obviously, when aircraft are ascending or descending, the risk of collision
increases. But you can only rely on ATC in IMC to reduce this risk, or use
"see and avoid" in VMC.

And I am aware that there are other IFR separation methods such as takeoff
sequencing and timing, maintaining separation via speed, flying your flight
plan exactly if something goes wrong, and similar methods, but they aren't
really germane to this limited discussion.





Pete