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Old August 9th 04, 10:43 PM
Stan Prevost
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"Snowbird" wrote in message
m...
"Stan Prevost" wrote in message

...


I did not intend to assert that only H-class VORs are likely to be
recognized nationwide -- that's not true. It seems to vary from
center to center. Any VOR on an airway is a fairly good bet some
places.


big snip

OK, I see that I interpreted your comments about H-class VORs too broadly,
and I now understand your meaning better.



It would seem
logical to me (for whatever that has to do with anything) that any VOR

used
to *define* airways, low- or high-altitude, would be recognized by any
computer that has anything to do with flights on the airway structures

of
the National Airspace System.


My husband would say something like "Stan, this is the federal
government.
You're expecting it to be logical. There's your mistake. There's
where
you're going wrong". (since he rassles federal regs for a living, he
has a right to an opinion).


:-) Yep, but you will notice that my parenthetical remark disclaimed the
application of logic to a gov't system.


What I *think* is going on, though, is that the airway itself is
understood
by the computer, but the specific navaids which define it in, say,
ZKC airspace, might be unknown to the computers in Miami Center. So
if
you route by airways, you're gold, but if you pick a non-H class VOR
two centers away as one of the few waypoints defining a direct route,
it might not be recognized even if it's on an airway.

I await further enlightenment on this point.


Me too!

The first thing is to understand the controller's needs for route
definition, specifically for a direct flight for this discussion. One might
expect that the controller would be concerned only with the route through
his airspace, so he couldn't care less about the route definition way down
the line. Does he need to be able to make my course line appear on his
radar scope all the way through his airspace? Or does he just need a
short-term projection of my track using radar for present position,
direction, and speed? Probably one need is to be prepared to handle radar
failure. In nonradar procedures, I think they try to move us all onto
airways, and to do this, the panicked controller needs to know which airways
to move us onto that keep us going in the proper general direction and out
of his airspace (or maybe the computers suggest new airway routing). So how
does knowing one VOR-based fix in his airspace do that? Does he have his
computer draw a line on his scope from present position through the fix, so
that he can then pick airways that approximate that route?

The next thing is to understand what the ATC computers are capable of and
how much variation there is among them, in terms of storage/knowledge of
fixes.

But eventually, no matter how well we understand those things, we will come
back to the old oft-debated issue of no matter what you file, you will get
something different or will get major reroutes, so you might as well file
direct airport to airport. I am sure this is more true in some areas than
others, based on my own experience, and for frequently-flown routes, one can
eventually learn reliable routing. Up through the northeast corridor, I
always get reroutes. In the east-central US, I can file from Alabama to
northern Lower Michigan airport-to-airport direct and always get cleared as
filed with no reroutes. I do this frequently. Many times, flying to other
destinations, I have tried to tweak my route to include some major VORs,
only to get an in-flight clearance direct to destination airport.

3. Newps said that his FDIO won't accept intersections that are not in

his
center's airspace, but that filing through DUAT/S and AFSS does not have
that limitation. I would expect that virtually all general aviation IFR
flight plans are entered via DUAT/S or FSS, excluding local clearances

to
punch through a layer or for instrument practice. And back to Sydney's
comment quoted above, I don't know what she means by the "originating

ATC
facility".


I apologize for being unclear. I wasn't talking about filing a flight
plan. As you say, that's usually through FSS or DUATS. DUATS will
accept
a flight plan direct from an obscure intersection in CA to an obscure
intersection in FL. So will FSS as far as I know (I haven't tried).
Duats will insert one lat-long per center. FSS doesn't seem to.


When I file through DUAT, it doesn't do one lat/long per center, it only
does the final fix.


What I mean by the "originating ATC facility" is the ATC facility you
talk to after you leave the ground, or the first Center you talk to.


Thanks, I understand your reference now

Or maybe she means the center through which the
flight plan is routed for processing after it is filed, and I really

don't
know what happens there.


That's what I mean. I really don't know what happens there, I
just know what happens to me .

Now if you've filed airway routing, I'm told an unrecognized
intersection or waypoint at the end of the route is no big deal.
The flight plan gets processed to the unrecognized point. The first
controller will know which way you're going, and by the time it
matters, the ATC computer will recognize it. Which is why Don Brown
and some others favor airway routing, and I have to say I'm
coming around to that viewpoint myself.

It's mostly an issue if, like many pilots these days, you file
GPS direct but feel you're making the skies safer or your karma
cleaner or something by adding the IAF from which you plan to shoot
an approach to your route. Or, let's say you've read the AIM and
you virtuously add a waypoint defining your route within 200 nm
of each center boundry. Let's say it's a VOR.


big snip

I don't see any difference between filing airport-IAF-airport vs
airport-airport, in terms of fix recognition and controllers knowing your
route. If the IAF (or other nearby fix) is there, it likely won't be
recognized by a distant computer (another center's airspace). But neither
will the airport. Maybe some airports are in all computers, but going into
Podunksville Muni, forget it. "N8158Y, say on-course heading." (Having
lat/long in the flight plan for the final enroute fix or for the destination
doesn't seem to change getting the heading request.) In either case, at the
originating end and along the way, the controllers will be in the dark about
your route, but the situation resolves itself as the flight nears its
destination.


What can happen -- what's happened to us -- is that the tower
controller doesn't worry his head about your flight plan. He
figures the tracon's gonna vector you and the center's gonna
reroute you anyway so why should he sweat. He says "cleared
as filed". Now you're handed off to Tracon, and he looks at
your flight plan and realizes he has no clue where you're going.
But he figures you'll be out of his airspace before he sorts
it out, so let the center controller sweat it. He queries,
"Grumman 12345, say on-course heading", you respond, and
that's sufficient for him. 10 minutes later, you're handed
off to Center.

Well, the next Center isn't going to be fobbed off with
"on-course heading blahblahblah" on the handoff, so the buck
stops with the first Center guy (this is our experience, mind,
YMMV).

This is when we, as pilots, get to learn by trial and error
which waypoints and airports aren't recognized by different
Center ATC computers as the controller says "um, Grumman 12345,
can you give me the lat-long for India One-Twelve, or a VOR near
it? No, I don't have that one...can you give me a VOR on
your route of flight, within my airspace?" Needless to say,
if ATC is busy, this totally lacks amusement value for them.
If ATC isn't busy but the wx is challenging, it lacks amusement
value for us.


One would think that the DUAT/S systems
were designed to only transmit flight plans to centers that would be
acceptable to centers, in terms of recognizability of waypoints.


There you go, expecting the federal government to be logical
again. That's where you're going wrong. That's your mistake.


Yeah, there's that logic thing again. But, joking aside, I really do expect
that the DUAT/S contractors operated to an interface specification of some
kind in designing their systems, and do not output data that will not be
understood by the receiving computers.

It seems to me that a US pilot filing domestic IFR through DUAT/S or FSS

is
safe using any valid identifiers s/he wishes, in terms of having the

flight
plan accepted and properly processed by the NAS computers.


What do you mean by "safe", Stan? (see above)

If you mean, ATC will understand which direction you're going and
how your route is defined provided you use any valid identifiers
accepted by FSS or DUATS, IME that's just not so.


Perhaps a poor term, but I meant it as I said, that the flight plan will be
accepted and properly processed by the NAS computers. To clarify my
meaning, I understand that the flight plan is routed from DUAT/S or FSS to
the center computer having jurisdiction over the departure point. That
machine looks at the proposed route, applies some secret algorithms and
decides whether to accept the route or to discard it and generate a new
route, maybe a preferred route. I meant that a flight plan accepted by
DUAT/S or FSS will not be rejected by the center computer because of an
unrecognized waypoint.

It may be the case that this computer that processes proposed flight plans
is completely unrelated to those that assist (?) controllers move airplanes.
It may be the case that the former has a complete database and the latter do
not.

I'm obviously doing a lot of guessing here, but we ought to be able to
reconcile things. FSS and DUAT/S plans do not get rejected because of
unrecognized waypoints, but all of us have experienced that enroute
controllers do not have access to a complete database. That suggests two
separate systems.

Stan