GPS approach step-down fixes

As far as I can see, step-down fixes on GPS approaches are always defined by
a distance to the threshold. Are there exceptions?

Do GPS approaches exist with waypoints (forming part of the approach
sequence) between the FAF and the runway threshold waypoint? Or is it
guaranteed that after passing the FAF, my distance-to-waypoint will always
be the distance to the threshold?

Counter-examples useful. References to publications guaranteeing no
counter-examples even better!

Thanks

Julian

Julian Scarfe wrote:

As far as I can see, step-down fixes on GPS approaches are always defined by
a distance to the threshold. Are there exceptions?

Do GPS approaches exist with waypoints (forming part of the approach
sequence) between the FAF and the runway threshold waypoint? Or is it
guaranteed that after passing the FAF, my distance-to-waypoint will always
be the distance to the threshold?

Counter-examples useful. References to publications guaranteeing no
counter-examples even better!

Thanks

Julian


The criteria are evolving and changing. You have to take each procedure
as it is charted and as it appears in your database.

"Julian Scarfe" wrote in message ...
As far as I can see, step-down fixes on GPS approaches are always defined by
a distance to the threshold. Are there exceptions?

Do GPS approaches exist with waypoints (forming part of the approach
sequence) between the FAF and the runway threshold waypoint? Or is it
guaranteed that after passing the FAF, my distance-to-waypoint will always
be the distance to the threshold?

Counter-examples useful. References to publications guaranteeing no
counter-examples even better!

Thanks

Julian

Did you mean strictly "distance to the threshold"?
Where the Missed Approach Point is short of the threshold,
stepdown fixes are likely to be defined by distance to the MAP.
In Colorado, here are a few examples which illustrate that:
KCAG (Craig) GPS Rwy 7
KDRO (Durango) GPS Rwy 2
KEGE (Eagle County) GPS-D
KHDN (Hayden) RNAV (GPS) Y Rwy 10
KLXV (Leadville) GPS Rwy 16
KMTJ (Montrose) GPS Rwy 17, GPS Rwy 35
KRIL (Rifle) GPS Rwy 8, GPS Rwy 26
Most of those stepdown points are defined only by distance,
but at least in the case of Hayden, ZULON is a named stepdown fix,
at 1.9 nm to RAPVE, which is the MAP located 1 nm from the runway.

John R. Copeland wrote:

"Julian Scarfe" wrote in message ...

As far as I can see, step-down fixes on GPS approaches are always defined by
a distance to the threshold. Are there exceptions?

Do GPS approaches exist with waypoints (forming part of the approach
sequence) between the FAF and the runway threshold waypoint? Or is it
guaranteed that after passing the FAF, my distance-to-waypoint will always
be the distance to the threshold?

Counter-examples useful. References to publications guaranteeing no
counter-examples even better!

Thanks

Julian


Did you mean strictly "distance to the threshold"?
Where the Missed Approach Point is short of the threshold,
stepdown fixes are likely to be defined by distance to the MAP.
In Colorado, here are a few examples which illustrate that:
KCAG (Craig) GPS Rwy 7
KDRO (Durango) GPS Rwy 2
KEGE (Eagle County) GPS-D
KHDN (Hayden) RNAV (GPS) Y Rwy 10
KLXV (Leadville) GPS Rwy 16
KMTJ (Montrose) GPS Rwy 17, GPS Rwy 35
KRIL (Rifle) GPS Rwy 8, GPS Rwy 26
Most of those stepdown points are defined only by distance,
but at least in the case of Hayden, ZULON is a named stepdown fix,
at 1.9 nm to RAPVE, which is the MAP located 1 nm from the runway.


As I said:

"The criteria are evolving and changing. You have to take each
procedure as it is charted and as it appears in your database."

"John R. Copeland" wrote in message
...

Did you mean strictly "distance to the threshold"?
Where the Missed Approach Point is short of the threshold,
stepdown fixes are likely to be defined by distance to the MAP.

You're right, I meant distance to MAP, not distance to threshold. So
perhaps that changes the question into whether there are waypoints on the
approach between the FAF and the MAP.

KHDN (Hayden) RNAV (GPS) Y Rwy 10

but at least in the case of Hayden, ZULON is a named stepdown fix,
at 1.9 nm to RAPVE, which is the MAP located 1 nm from the runway.

OK, good example. So when I pass INEDE (the FAF) inbound on that approach,
what does my distance-to-waypoint read? 3.5, counting down to ZULON, or 5.4
counting down to RAPVE?

Julian

"Julian Scarfe" wrote in message ...
"John R. Copeland" wrote in message
...


KHDN (Hayden) RNAV (GPS) Y Rwy 10

but at least in the case of Hayden, ZULON is a named stepdown fix,
at 1.9 nm to RAPVE, which is the MAP located 1 nm from the runway.

OK, good example. So when I pass INEDE (the FAF) inbound on that approach,
what does my distance-to-waypoint read? 3.5, counting down to ZULON, or 5.4
counting down to RAPVE?

Julian

I've run several other examples through the GNS480 simulator,
and they all have computed a smooth glide path from the FAF to the MAP,
displaying nothing regarding the named stepdown fixes.
The distance counts down from the FAF to the MAP, as in your supposition.

I don't know of any approaches near me with suitable stepdown fixes
to try actually flying one for real.
But previously I've found the simulator to be very faithful to the actual equipment.

If you have the GNS430/530 simulator, try running some approaches on it.
It might behave differently, since it would not supply vertical guidance.

"John R. Copeland" wrote in message
.. .

If you have the GNS430/530 simulator, try running some approaches on it.
It might behave differently, since it would not supply vertical guidance.

Thanks, I'll give it a go.

Julian

"Peter" wrote in message ...

The other question I would ask here is whether an FAA approved IFR GPS
is *capable* of continuously displaying the distance to the MAP,
during the flight from the FAF to the MAP, if there are *any*
waypoints between the two.

I don't think it is. I don't think it's possible to have

FAF X Y Z MAP

and somehow force the GPS to display the distance *to the MAP* while
one is flying past X,Y,Z.

The GPS will always display the distance to the next waypoint in the
database.

In other words, I don't think it's possible to get the GPS to produce
a DME-like distance readout.

One way to achieve a distance readout to some waypoint which is past
the current one would be to have a sort of "invisible" attribute on a
waypoint (in the GPS database) causing the GPS to ignore it for the
distance calculation.

Yes, it is possible for at least some GPSs to do what you doubt.
I don't have a TSO-C129 GPS to compare with,
but my TSO-C146 unit will display distance to MAP, ignoring stepdowns,
but possibly only when it can compute an uninterrupted glide path to MAP.
In that case, even though named stepdown fixes exist, they aren't used.
That's the behavior I've seen in the U.S.; I don't know the rules behind it.

Of course, in the UK, with EGNOS not yet available,
TSO-C146 units could not compute that glide path,
so I shouldn't try to guess what they'd do without augmentation.
But I'd expect them to revert to TSO-C129-like behavior.
I think Julian may experiment with a Garmin 430/530 simulator,
and he'll surely tell us if he turns up behavior different from the GNS480.