"Snowbird" wrote in message
om...

I think two of Don's concerns with lat-longs a
1) they provide ATC with no information about what direction you're
headed, so coordination with other facilities is difficult. In fact,
initial separation is problematic.


Well, that's certainly true if you're unfamiliar with latitude and
longitude. Of course, the same situation exists when the pilot files direct
to an identifier the controller is unfamiliar with.



2) ATC apparently has no means to verify a lat-long against an
airport identifier or navaid to ensure that the lat-long was entered
correctly. Serious lack of backup or verification redundancy.


So what? There's also no means to verify that the identifier the pilot
filed direct to is actually the identifier he intended to file.



I don't know about you, but I don't want to be in either place.

My suggested solution for filing GPS direct is:
1) provide a VOR radial-distance waypoint which will be recognized --
one w/in the facility's boundry is a good bet. That way ATC knows
which direction you're headed from a waypoint which will be in their
host computer, and coordination is easier for them


That will work fine as long as your flight doesn't cross a center boundary.



2) put a radial-distance from a VOR near your destination into your
flight plan. if you're crossing several centers, make sure there's
one in each center.


That doesn't guarantee that your flight plan will be accepted by all center
computers. Any given Center does not necessarily recognize all the VORs
that are in adjacent Centers.



I note that the above does not fulfil the letter of the AIM for
direct flights, which require that a direct flight begin and end
over a ground-based navaid (at least as I read it) but I feel
it fulfills the spirit, in that it allows ATC to know which way
I'm headed without guessing and to verify any lat-longs in a
straighforward way.


It allows ATC to know which way you're headed only if they recognize the
base navaid. Unlike filing latitude/longitude, filing a distance and
azimuth from an unknown VOR provides no information by itself.

Why would ATC need to verify any lat-longs?



This said: I don't understand your comment about why one should
file lat-longs. Yes, VORS outside a center's airspace might
not be in the host computer, but this doesn't stop pilots from
flying Victor airways or direct VOR routing which includes
VORs the ATC computer for the facility originating the flight
won't recognize. What I know about ATC host computers could be
printed on a penny and lost, but surely they have some mechanism
for accepting "I don't know where that VOR is, but the routing
through my part of the system looks OK so off you go".


Each Center computer processes the flight plan only to the first fix outside
it's airspace. As long as each computer can process to that fix,
everything's fine. The problem arises when the computer gets to a known fix
in it's own airspace but does not recognize the next fix. It doesn't know
where the flight is going from that point, so it stops processing and prints
XXX on the route after the last good fix.

Incidentally, filing airways does not necessarily avoid this problem. If
the computer doesn't recognize a valid fix on an airway, usually some
distant intersection, it doesn't know where to go either. For example,
let's say you file 1H0..STL.V14.BALDY..ORE. It's a perfectly valid route,
it's in the proper format, all the elements are correct. The problem is V14
extends from New Mexico to Massachusetts, and if the Kansas City computer
doesn't recognize BALDY, (and it probably does not), then it doesn't know
which way to go once you hit STL.



In a sane world, of course, each controller would be able to
instantly convert a lat-long into some bearing from a recognizeable
navaid or airport. It could be done on a used $50 Palm Pilot.
But that would make too much sense.


The controller doesn't need to instantly convert a lat-long into some
bearing from a recognizable fix. The Center computer is going to do that
for him. While the route will show the filed latitude/longitude fixes, each
printed strip in each Fix Posting Area will show an estimated time over a
degree and distance fix from the Focal Point Fix for that Fix Posting Area.