Don Brown and lat-long

"Bob Gardner" wrote in message news:oAHab.386624$Oz4.170720@rwcrnsc54...
I did not intend that pilots file lat-longs exclusively

*puzzled* did I say or imply that you did?

just when they need
something far enough away from the departure airport that a radial-distance
might not be in the local host computer.

Perhaps I did not explain clearly enough what I don't understand
about your advice. (I assume you mean "VOR" or "radial distance
from VOR" above. I also assume that by "local host computer"
you mean the ARTCC host computer.)

I don't understand the necessity of filing a lat-long in
any circumstance.

People file and fly Victor airway or direct VOR routing where
many of the waypoints are not in the host computer of the
originating ATC facility. For that matter, people file to
airports which aren't in the originating ATC facilities
host computer all the time.

How could this work, if (as you imply) a routing which contains
waypoints not in the ATC host computer is a problem?

It seems to me that it's a problem only if the destination,
and the distant VOR from which the radial-distance is measured,
are the ONLY waypoints in the flightplan.

In that case, I suggest that the solution is not to tell people
"go ahead and file lat longs". The problem is to tell people
"file enough waypoints to define your route locally".

If I'm wrong, and the host computer will indeed barf on an
IFR routing which contains a VOR radial-distance to a VOR
not in the database, I wait to be corrected. But in that
case, I don't understand how filing an IFR routing which
includes direct-VOR-VOR segments that the local host doesn't
know about works, either.

IOW, I don't understand what problem requires lat-longs to
solve it. And yes, we've flown trips where the VOR radial-
distance we chose turned out to be just outside one center's
airspace and we were requested to give them a VOR or VOR
radial-distance w/in their airspace which defined our route,
so I understand the problem of ATC host computers which store
fewer waypoints than my obsolete Palm VIIx. I just don't see
how filing a lat-long would solve any problem.

Perhaps I'm just dense.

Cheers,
Sydney

(Snowbird) wrote in
m:

I don't understand the necessity of filing a lat-long in
any circumstance.

Well, down here in the Gulf of Mexico, that's about the only way
to do it. We file to/from a lat/lon, & in the remarks put the
offshore block number. Those numbers are not in any particular
order, because they were created by the guv'mint as new blocks
became necessary when oil companies wanted to drill in new
places. They're a confusing mess, and nobody knows where blocks
are precisely without looking closely at a map. But we do have
to go to and from them IFR. The solution is lat/lon. ATC may
still not know our exact (or even approximate) direction of
flight, but a quick query will get it from us. There may be
more reasons for using coordinates onshore. The IFR world is
not entirely defined by Cessna 172's flying from airport to
airport.

--
Regards,

Stan

First, I'm just passing along advice that I got from a Baron-operating
controller on the west coast. I have to assume that he knows the system
better than I do. Second, we are talking about filing direct, not via
airways. His argument, which I am not in a position to refute, is that every
host computer in the National Airspace System can find a lat-long, while
that is not true of every radial-distance.

Bob Gardner

"Snowbird" wrote in message
m...
"Bob Gardner" wrote in message
news:oAHab.386624$Oz4.170720@rwcrnsc54...
I did not intend that pilots file lat-longs exclusively

*puzzled* did I say or imply that you did?

just when they need
something far enough away from the departure airport that a
radial-distance
might not be in the local host computer.

Perhaps I did not explain clearly enough what I don't understand
about your advice. (I assume you mean "VOR" or "radial distance
from VOR" above. I also assume that by "local host computer"
you mean the ARTCC host computer.)

I don't understand the necessity of filing a lat-long in
any circumstance.

People file and fly Victor airway or direct VOR routing where
many of the waypoints are not in the host computer of the
originating ATC facility. For that matter, people file to
airports which aren't in the originating ATC facilities
host computer all the time.

How could this work, if (as you imply) a routing which contains
waypoints not in the ATC host computer is a problem?

It seems to me that it's a problem only if the destination,
and the distant VOR from which the radial-distance is measured,
are the ONLY waypoints in the flightplan.

In that case, I suggest that the solution is not to tell people
"go ahead and file lat longs". The problem is to tell people
"file enough waypoints to define your route locally".

If I'm wrong, and the host computer will indeed barf on an
IFR routing which contains a VOR radial-distance to a VOR
not in the database, I wait to be corrected. But in that
case, I don't understand how filing an IFR routing which
includes direct-VOR-VOR segments that the local host doesn't
know about works, either.

IOW, I don't understand what problem requires lat-longs to
solve it. And yes, we've flown trips where the VOR radial-
distance we chose turned out to be just outside one center's
airspace and we were requested to give them a VOR or VOR
radial-distance w/in their airspace which defined our route,
so I understand the problem of ATC host computers which store
fewer waypoints than my obsolete Palm VIIx. I just don't see
how filing a lat-long would solve any problem.

Perhaps I'm just dense.

Cheers,
Sydney

"Bob Gardner" wrote in message
news:Rg0bb.393287$cF.121073@rwcrnsc53...
First, I'm just passing along advice that I got from a Baron-operating
controller on the west coast. I have to assume that he knows the system
better than I do. Second, we are talking about filing direct, not via
airways. His argument, which I am not in a position to refute, is that
every
host computer in the National Airspace System can find a lat-long, while
that is not true of every radial-distance.


He's correct about that. Lat/longs always work for flight data purposes.
However, this really is a deep subject. When I get out of the throws of
this work week (which I'm right in the middle of) I'll try to post some of
my opinions and observations on this subject. I tend to be with you in the
lat/long camp myself, but with a host of preconditions which I will
hopefully be able to share in this thread in a couple of days.


Chip, ZTL

"Snowbird" wrote in message
m...

If I'm wrong, and the host computer will indeed barf on an
IFR routing which contains a VOR radial-distance to a VOR
not in the database, I wait to be corrected.


It will barf if it is asked to actually process to that fix. If there's
another known fix outside it's area prior to that VOR radial-distance to a
VOR that's not in it's database, no problem.

"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.

"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.

Initial separation is never problematic, that's what vectors are for.


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.

I don't care if you entered the lat/lon correctly. Only the last
controller cares.


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

Doesn't matter to ATC. File direct, we will figure it out. If we have
to. I have cleared many aircraft to a three letter identifier and never
known the name of the airport. If I need it I will ask for his on
course heading, say resume own nav and there he goes.



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.

I can't even hazard a guess as to how many of these carefully concocted
flight plans I have erased and changed to direct to destination. DUATS
is usually an instigator of these ridiculous plans.



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

Not necessary.


(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.

ATC does not care about lat/lons and your requested altitude will
usually give a heads up of your general direction. If I need to know I
can always look up your destination airport(or any other fix) in our
location ID book.