Flying IFR with Garmins

On Mon, 21 Jun 2004 08:11:04 +0100, "Julian Scarfe"
wrote:

I do the same and I have an STEC 60-2.

The problem seems to be the tracking algorithm. If you're slightly off
track a/p turns the aircraft through, say, 20 degrees, and waits for a CDI
movement.

I have an STEC50 and a CNX80.

The CNX80 has airways, so regardless of how I am cleared, I track enroute
using GPS mode.

As recommended by STEC, I use the APR mode for tracking a GPS course.

My off-track distance does vary, but by usually less than 1000'. In
heading mode, I will eventually drift off that much, or more. The turns
are rarely more than five degrees, once centered.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

"Ron Rosenfeld" wrote in message
...

As recommended by STEC, I use the APR mode for tracking a GPS course.

That could get entertaining if you pick up a glide slope while
you're at altitude....

On Tue, 22 Jun 2004 12:15:06 -0700, "John Harper"
wrote:

That could get entertaining if you pick up a glide slope while
you're at altitude....

How would that happen?


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Not sure what you mean. The glide slope goes on for
ever, it doesn't stop at the outer marker. Given the
right runway and a powerful enough receiver, you could
pick it up on Pluto. (Voyager transmits on 2W or so).

So there you are at 15000' in APP mode and you
pick up a GS, whereupon the autopilot will start a
coupled approach and start you on down the glideslope.
My understanding is that the only difference between
APP and NAV modes is whether the GS coupling
is enabled. If the GS and dest waypoint happen to be in much
the same direction you could get a long way down...

Of course you'd spot this happening and recover (right?)
but still it would be an interesting moment.

John

"Ron Rosenfeld" wrote in message
...
On Tue, 22 Jun 2004 12:15:06 -0700, "John Harper"
wrote:

That could get entertaining if you pick up a glide slope while
you're at altitude....

How would that happen?


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

"John Harper" wrote:
..
My understanding is that the only difference between
APP and NAV modes is whether the GS coupling
is enabled.

Nope. On an S-TEC 50, the only difference between APP and NAV is the
degree of sensitivity to CDI deflection: APP is more sensitive. The 50
does not do VNAV; there's now way it could "pick up the glide slope."

In my airplane, I set the S-TEC 50 to APP and the KLN-90B GPS CDI output
to 1.0 mile. This setup keeps me on course with a cross track error of
50'.
--
Dan
C172RG at BFM

On Tue, 22 Jun 2004 14:20:18 -0700, "John Harper"
wrote:

Not sure what you mean. The glide slope goes on for
ever, it doesn't stop at the outer marker. Given the
right runway and a powerful enough receiver, you could
pick it up on Pluto. (Voyager transmits on 2W or so).

Yeah, but you have to have a receiver tuned to that frequency, don't you?
At least with the receivers I've used in light GA a/c, I've not picked up a
GS signal without tuning to the appropriate frequency.

You would also need to have the CDI in the GPS receiver set to output the
VOR/LOC signal, and not the GPS signal information.


So there you are at 15000' in APP mode and you
pick up a GS, whereupon the autopilot will start a
coupled approach and start you on down the glideslope.
My understanding is that the only difference between
APP and NAV modes is whether the GS coupling
is enabled.

With respect to the STEC50, your understanding is incorrect. The
difference has to do with sensitivity to the signal. And there is no GS
coupling with my STEC50.

If the GS and dest waypoint happen to be in much
the same direction you could get a long way down...


Do other GPS receivers allow you to navigate with both a GPS signal, and
some random GP signal that happens to be in the same direction? The CNX80
certainly does not.


Of course you'd spot this happening and recover (right?)
but still it would be an interesting moment.

I can't imagine a failure mode that would result in this scenario.

Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Hmm. Yep, I guess you're right. You'd have to be
tuned to an ILS for this to happen (even assuming
you have an a/p that does coupled approaches),
and have the GPS in VLOC mode (well I suppose
so, I haven't actually checked to see if the HSI
tracks the GS if you have the 530 tuned to an ILS
but in GPS mode, it would be odd if it did).

I guess I just had it drummed into me not to use APP
mode unless you really mean it, and this was the
rationale. I don't know if my a/p does anything
different in APP mode, other than GS tracking.
Certainly the GPS is more sensitive when you get
within 30 miles of the destination. And my a/p
works a lot better in that case for NAV tracking,
which is what makes me think it could be made
to work well in normal mode too.

John

"Ron Rosenfeld" wrote in message
...
On Tue, 22 Jun 2004 14:20:18 -0700, "John Harper"
wrote:

Not sure what you mean. The glide slope goes on for
ever, it doesn't stop at the outer marker. Given the
right runway and a powerful enough receiver, you could
pick it up on Pluto. (Voyager transmits on 2W or so).

Yeah, but you have to have a receiver tuned to that frequency, don't you?
At least with the receivers I've used in light GA a/c, I've not picked up
a
GS signal without tuning to the appropriate frequency.

You would also need to have the CDI in the GPS receiver set to output the
VOR/LOC signal, and not the GPS signal information.


So there you are at 15000' in APP mode and you
pick up a GS, whereupon the autopilot will start a
coupled approach and start you on down the glideslope.
My understanding is that the only difference between
APP and NAV modes is whether the GS coupling
is enabled.

With respect to the STEC50, your understanding is incorrect. The
difference has to do with sensitivity to the signal. And there is no GS
coupling with my STEC50.

If the GS and dest waypoint happen to be in much
the same direction you could get a long way down...


Do other GPS receivers allow you to navigate with both a GPS signal, and
some random GP signal that happens to be in the same direction? The CNX80
certainly does not.


Of course you'd spot this happening and recover (right?)
but still it would be an interesting moment.

I can't imagine a failure mode that would result in this scenario.

Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

On Tue, 22 Jun 2004 17:56:11 -0700, "John Harper"
wrote:

I guess I just had it drummed into me not to use APP
mode unless you really mean it, and this was the
rationale. I don't know if my a/p does anything
different in APP mode, other than GS tracking.
Certainly the GPS is more sensitive when you get
within 30 miles of the destination. And my a/p
works a lot better in that case for NAV tracking,
which is what makes me think it could be made
to work well in normal mode too.

Well, the reason I started using APP mode for tracking GPS was because that
was the recommendation of the a/p manufacturer! (Stec in this case). And,
being more sensitive, there is less course wandering. Since the signal is
more stable than a VOR signal, it made sense to me to follow the mfg
recommendation.

I never had the (mis)fortune of having someone drum into me anything about
using the a/p :-)




Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

"John Harper" writes:

My understanding is that the only difference between
APP and NAV modes is whether the GS coupling
is enabled. If the GS and dest waypoint happen to be in much
the same direction you could get a long way down...

Your understanding is incorrect.

One of the differences between NAV and APR mode is how aggressive the
a/p will be to keep the needle centered.

The GS capture is not armed unless you have a localizer frequency
channeled in (ie, tuned in a nav radio, and the a/p is coupled to
that radio), among other things.

-jav

If the 430 is in GPS mode, it won't output GS information.

Mike
MU-2


"John Harper" wrote in message
news:1087931861.386166@sj-nntpcache-3...

"Ron Rosenfeld" wrote in message
...

As recommended by STEC, I use the APR mode for tracking a GPS course.

That could get entertaining if you pick up a glide slope while
you're at altitude....