GPS approach question

"CFII_ASC" wrote:

Typically, to get it to go into the ACTV mode, these things must be
true:
1. In LEG mode (not OBS)
2. In ARM mode (this comes up when you have a valid approach loaded,
and you are within 30nm)

Within 30 nm of what? The IAF? The destination?

3. Valid RAIM now, and predicted at FAF and MAP
4. Outside FAF (110 degree arc each side of FAF)
5. Distance to FAF decreasing
6. Within 2nm of FAF, but not past (inside) FAF
7. NAV/GPS switch must be in the GPS position
8. No localizer frequency may be loaded into NAV 1 (some boxes)

Wow, that last one is pretty strange. I often have an ILS frequency
loaded up, even if I'm not using it. The most frequent use I make of
the NAV part of the GPS/NAV/COM is to fly an ILS, so the last ILS flown
is usually what's left there. What is the logic behind requiring me to
change it to something else?

I don't have the book here, but I *believe* the 30nm is referenced to
the Airport Reference Point, which is the physical location from which
they began the survey of the land to lay out the airport. Mostly this
is somewhere near the center of the airport, but not always. sometimes
it is not even *on* the airport.

The last issue, #8, is implemented on some boxes and not others. I do
not remember if the 89B had that feature or not. But on some machines
it was wired to automatically switch the NAV/GPS switch back to NAV if
you had a valid Localizer freq in Nav 1. The theory was that if you
were trying to fly an ILS and fogot your NAV/GPS switch was left in the
GPS position, it would automatically default back to the NAV position
so that the data displayed on the needle you were tracking was from the
ILS and not the GPS (that you were presumably not using.)

Of course, this created the opposite problem; if you are trying to do a
GPS approach, and forget to get the ILS freq out of Nav 1, it would not
allow you to *load* the approach, let alone fly it. Infuriating.

I have not seen this feature implemented on any of the more recent
boxes.

Bottom line, you have to know what your box does and doesn't do
automatically, and when it does it, and why. An put a check of that
NAV/GPS switch in your set-up procedure for *all* your approaches, not
just the GPS ones.

Regards,

Gene

"CFII_ASC" wrote:
Bottom line, you have to know what your box does and doesn't do
automatically, and when it does it, and why. An put a check of that
NAV/GPS switch in your set-up procedure for *all* your approaches, not
just the GPS ones.

Yeah, I've been burned by that one, and it's one of the most common
mistakes I see students make.

The other common one (at least on the CNX-80) is to forget to hit the
EXEC button after modifying a flight plan or selecting an approach.

"Roy Smith" wrote in message
...
Wow, that last one is pretty strange. I often have an ILS frequency
loaded up, even if I'm not using it. The most frequent use I make of
the NAV part of the GPS/NAV/COM is to fly an ILS, so the last ILS flown
is usually what's left there. What is the logic behind requiring me to
change it to something else?

Many, if not all, IFR GPS units and or switching relay/annunicators have an
option (often wiring) to force the switching relay to NAV if there is a LOC
frequency selected. In the newer integrated units, this "relay" is inside
the box.

Mike
MU-2

Roy Smith wrote:
"CFII_ASC" wrote:


Typically, to get it to go into the ACTV mode, these things must be
true:
1. In LEG mode (not OBS)
2. In ARM mode (this comes up when you have a valid approach loaded,
and you are within 30nm)


Within 30 nm of what? The IAF? The destination?

The FAF, I think, but someone else will give a more authoritative answer.



3. Valid RAIM now, and predicted at FAF and MAP
4. Outside FAF (110 degree arc each side of FAF)
5. Distance to FAF decreasing
6. Within 2nm of FAF, but not past (inside) FAF
7. NAV/GPS switch must be in the GPS position
8. No localizer frequency may be loaded into NAV 1 (some boxes)


Wow, that last one is pretty strange. I often have an ILS frequency
loaded up, even if I'm not using it. The most frequent use I make of
the NAV part of the GPS/NAV/COM is to fly an ILS, so the last ILS flown
is usually what's left there. What is the logic behind requiring me to
change it to something else?

The GX50 I had installed in my old Archer worked that way. I've also seen a GX50
that didn't work that way. It must be an installation option.

In the plane that wasn't installed that way, I've been safety pilot and seen a
confused pilot when he tuned the localizer without switching the GPS/NAV switch
to NAV, and couldn't figure out why the OBS wasn't behaving the way he thought
it should. OTOH, I can imagine the inverse kind of confusion occurring if the
OBS switched to NAV mode on its own when a localizer is tuned. You have to know
your installation.

What is the logic? Dunno.

On Tue, 04 Jan 2005 12:01:19 -0500, Dave Butler wrote:

Within 30 nm of what? The IAF? The destination?

The FAF, I think, but someone else will give a more authoritative answer.



the airport, if I am not mistaken.

Hah!

I looked it up. It is the ARP.

Gene

The GX50 is something of an oddity in some ways. I actually make a
fair amount of money just showing people how to set the OBS in that
box. It doesnt work like the others--wont read it from the external
display, you have to set it on the keyboard, and they hid it real good,
both on the box and in the manual.

For any GPS to be IFR approach approved, it has to drive an external
CDI indicator. In most installations, it shares the NAV1 indicator
with the #1 VOR receiver, and there is a switching unit on the panel
(somewhere), external to either the GPS or the indicator that controls
which box gets to talk to the display.

Some of the GX50 boxes came with their own, third display which is
dedicated to the GPS, so in these installations there is no NAV/GPS
switch.

The Garmin 430/530 boxes incorporate the #1 VOR rx and the GPS into the
same chassis, so on these boxes the NAV/GPS switch is a pushbutton on
the front of the box, rather than on an external panel. They also
renamed it: the button is labelled CDI, and the annunciator it controls
toggles between VLOC and GPS.

It helps to sit down with your avionics tech and make a block diagram
for your installation so you know how all this is hooked up--in *your*
airplane.

Think you got problems, consider the installation in a high-performance
single or twin, typically equipped with GPS, autopilot and DME:

NAV/GPS switch determines which box (VOR#1 or GPS) drives #1 CDI.
NAV1/NAV2 switch determines which CDI the autopilot follows.
Another NAV1/NAV2 switch determines which VOR rx is used by the DME for
remote automatic channeling.

These three switches are similar enough in appearance and function that
a lot of pilots get really screwed up. Add to this some faded out
labelling and you have a real opportunity to make a complete mess of
things. (Why is that guy in the F15 flying so close to me and waving?)
Gene

wrote in news:1104913014.473596.136650
@c13g2000cwb.googlegroups.com:

(Why is that guy in the F15 flying so close to me and waving?)

Minor nit. They don't use F15s, it's F16s. And they don't wave. DAMHIKT.

--
Regards,

Stan

Stan,

The point was not about the model airplane that would conduct the
intercept--but why. It is a little known 'stat' about GPS that since
we got them in little airplane cockpits the frequency of airspace
violations have *increased.* People seem to be getting 'head down and
locked' trying to wade through the many options and pages and modes on
the black box while not noticing what is happening outside, i.e.
penetrating airspace they do not have permission for.

In general you must be correct; ie all of the intercepts I have been
made aware of in recent years involved F16s--including one during Pres.
Regan's funeral that had the F16 driver doing wingovers around our
aircraft as we tooled down the ILS--he was intercepting some poor
gentleman off to our left in a little Ercoupe that had apparently 'not
gotten the word' as the saying goes.

I do know of one gentleman (who, due to his incident became my customer
under the remedial instruction program) who penetrated the restricted
area over Groom Lake, NV and was intercepted by an F15. I suppose it
has something to do with which types are based where.

In either case, it is not something you like to see--military jets
pulling up alongside your flight. I understand it is especially
unnerving if they happen to have other than US markings.

Regards,

Gene