GPS approach question

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

wrote in news:1105228604.387662.151640
@c13g2000cwb.googlegroups.com:

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.

I haven't seen other than US markings, but it's not unknown for other
countries to fly aircraft close to the coast, just to reinforce their
right, just as it's not unknown for foreign warships to steam a few miles
out. I have seen US aircraft intercept me, once because my transponder
had slipped a cog internally, and once because a P3 (!) decided to come
take a look, even though I hadn't penetrated the ADIZ, just playing
around as far as I could tell. It's not that frightening, really, it's
more amusing to see a jet fighter try to slow down enough to do an
intercept of a helicopter.

Almost all the fighters doing intercepts of ADIZ inbounds are F16s,
because that's the standard type, but entering restricted or prohibited
areas inland may result in whatever type is based there.

--
Regards,

Stan

Stan,

I was only kidding about the frightening part... little exaggeration.

My closest encounter with a military type was when I came around the
west end of Catalina island at low level, and as I rounded the corner
there was an F16 coming the other way doing the same thing in the other
direction.

It wasn't *that* close (nobody had to maneuver)... and he *did* wave.
Regards,

Gene

wrote in news:1105262338.845935.121730
@c13g2000cwb.googlegroups.com:

My closest encounter with a military type was when I came around the
west end of Catalina island at low level, and as I rounded the corner
there was an F16 coming the other way doing the same thing in the other
direction.

It wasn't *that* close (nobody had to maneuver)... and he *did* wave.
Regards,

We used to see jets low-level in Germany all the time. F4s were no
problem, because you could see the smoke trailing from them for miles.
The bad ones were the F101s, just a small fuselage and about 3 feet of
wing on the sides, flying at 500' or less at better than 500 knots. You
didn't see them until they passed just off to the side, waving and
grinning. I still hate to see an F101.

--
Regards,

Stan