Stan Prevost wrote:


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?

Course line? What course line?



Or does he just need a
short-term projection of my track using radar for present position,
direction, and speed?

Ain't got that either.


Probably one need is to be prepared to handle radar
failure.

Yeah, right. If the radar fails completely at a busy terminal airspace
you're screwed. We all are. The controller will attempt to knock the
cobwebs off his long unused nonradar procedures but the reality is
traffic comes to a grinding halt.


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).

In a suprise nonradar situation I would call the center to see if a
flight on a direct clearance is in radar contact. If so then he can
stay on his direct route. But this being Salt Lake Center they don't
much care if an aircraft is in radar contact so the aircraft would most
likely stay on his direct route.


So how
does knowing one VOR-based fix in his airspace do that?

I have a map.


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?

You don't go making up airways. In this situation you would give a guy
a heading to join an airway and reclear him via that airway. Separation
would instantly go 100% vertical, it's the easiest one to apply.




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.


99.9% of IFR flights out of Billings are as filed, so this is going to
depend on where you are.



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.

Minneapoils and Salt Lake give a lot of direct and vector to direct
clearances.



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.

Airway routing is necessary in really busy airspace because right now we
have no better, more efficient way of doing things. Get out into the
other 75% of the country and direct routings are the norm.



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.

You also need to understand what I see as an approach controller. The
strip that prints out of your arriving flight does not have your cleared
route on it. All it has is the destination airport and the time you
will be there. I don't need to know or even care what you filed or were
cleared for. You're landing here and you will be vectored as such.