I went and did some LNAV/VNAV approaches yesterday with a King KFC 200
autopilot. Looking for some tips with these autopilots on GPS approaches.

1. In NAV or APP mode the commanded rate of turn appears slower than in
HEADING mode. Spinning the HSI to the desired heading (often 90 degree
turns) caused the plane to try to go in the wrong direction, or the rate of
turn (slightly less than standard) caused an overshoot and didn't capture
the new course.

2. If flying in APP mode, and then making a step down in altitude, the AP
would not capture the glideslope (I've noticed this with ILS approaches as
well, even if intercepting the GS from below)

3. Of course, roll steering would be ideal, but barring this, is there a
better way to utilized the autopilot to fly these approaches?

4. Would it be better to fly in heading mode, and then engage approach mode
just prior to the FAF?

"Viperdoc" > wrote in message
...
>I went and did some LNAV/VNAV approaches yesterday with a King KFC 200
>autopilot. Looking for some tips with these autopilots on GPS approaches.
>
> 1. In NAV or APP mode the commanded rate of turn appears slower than in
> HEADING mode. Spinning the HSI to the desired heading (often 90 degree
> turns) caused the plane to try to go in the wrong direction, or the rate
> of turn (slightly less than standard) caused an overshoot and didn't
> capture the new course.

One problem that's endemic to an analog autopilot (IMOHO)

>
> 2. If flying in APP mode, and then making a step down in altitude, the AP
> would not capture the glideslope (I've noticed this with ILS approaches as
> well, even if intercepting the GS from below)

Intercepting from above or below?

>
> 3. Of course, roll steering would be ideal, but barring this, is there a
> better way to utilized the autopilot to fly these approaches?
>
> 4. Would it be better to fly in heading mode, and then engage approach
> mode just prior to the FAF?

If you want a significantly increased workload, but no, it's not better.

Have you run all the self tests? Sounds like the AP controller is not
working at 100%.

> What the KFC225 won't do is
>
> a) intercept a GS from above - I was given a dodgy final vector
> yesterday which led to that

Isn't that generally a bad idea anyway? I was taught that false lobes
could lead you to grief and a GS should always be intercepted from below.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

Jose wrote:
>> What the KFC225 won't do is
>>
>> a) intercept a GS from above - I was given a dodgy final vector
>> yesterday which led to that
>
>
> Isn't that generally a bad idea anyway? I was taught that false lobes
> could lead you to grief and a GS should always be intercepted from below.
>
> Jose

That's right - due to inevitable ground reflections, there
are always false glideslopes above the correct one. The
ICAO planning instructions require the procedure to be
planned so thet the GS is captured from below.

In the same way, the localizer capture planning rules
require an intercept angle below 45 degrees, preferably
30 degrees.

--

Tauno Voipio (avionics engineer, CPL(A))
tauno voipio (at) iki fi

"Tauno Voipio" > wrote in message
...
> Jose wrote:
> That's right - due to inevitable ground reflections, there
> are always false glideslopes above the correct one.

Would you be so kind as to explain that one? False glidescopes?

Matt Barrow wrote:
> "Tauno Voipio" > wrote in message
> ...
>
>>Jose wrote:
>>That's right - due to inevitable ground reflections, there
>>are always false glideslopes above the correct one.
>
>
> Would you be so kind as to explain that one? False glidescopes?

An ILS signal is finally created at the receiver antenna
as a combination of three signals which are sent separately.

(For the perfectionists: This is a simplified description).

A localizer antenna group is built of three sections: left,
center and right. There are several antennas per section,
often 4 to 8. The center section radiates a signal called CSB
(carrier and sidebands) which alone will create a centerline
display at the receiver. The side sections radiate a signal
called SBO (sidebands only) which contains a kind of difference
signal between the centerline signal and a side indication.
The left and right side signals are radiated in opposite phase,
so the right signal is positive when the left signal is negative.
When the side antennas are at equal distances from the aircraft
antenna, the side signals cancel at the receiver. When there is
a distance difference (as it is when the aircraft is off-centerline)
the side signals combine producing the corresponding side signal.

The glideslope is produced in the same way, but there is a problem:
We cannot install a proper bottom antenna, as it should be some
tens of feet below ground. Here, we have luck: If an antenna is
put above a conductive flat surface, the field pattern is similar
as the pattern with an opposite-phase antenna at the same distance
at the other side of the surface, and that is just what is needed
here. We'll use ground surface as the reflector to create the illusion
of a bottom antenna.

The pattern must then be tilted upward by the glideslope angle.
This creates an asymmetry in the pattern, and we get false
glideslopes above the correct one. For a 3 degree glideslope,
the first false glideslope is usually around 10 degrees.

HTH (hope this helps)

--

Tauno Voipio
tauno voipio (at) iki fi

> Would you be so kind as to explain that one? False glidescopes?

The glide slope signal gets reflected off the ground, and your receiver
hears the echo. Under some circumstances, it may interpret the echo as
a glide slope, and falsely display a fly up or fly down indication. If
you follow that, you will probably descend too steeply, and short of the
runway.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

On Apr 1, 6:31 am, "Viperdoc" > wrote:
> I went and did some LNAV/VNAV approaches yesterday with a King KFC 200
> autopilot. Looking for some tips with these autopilots on GPS approaches.
>
> 1. In NAV or APP mode the commanded rate of turn appears slower than in
> HEADING mode. Spinning the HSI to the desired heading (often 90 degree
> turns) caused the plane to try to go in the wrong direction, or the rate of
> turn (slightly less than standard) caused an overshoot and didn't capture
> the new course.

It's true. The rate of turn is somewhat reduced. Shouldn't turn the
wrong
direction unless turning 180 degrees. If you start the turn as
commanded by
the GPS, it will make it. If it goes the wrong way on a 90, there is
something
wrong with it.
>
> 2. If flying in APP mode, and then making a step down in altitude, the AP
> would not capture the glideslope (I've noticed this with ILS approaches as
> well, even if intercepting the GS from below)

If it's working right, it should intercept the gs from either attitude
mode or
altitude mode. The gs must pass thru center in either case and it may
be
slightly misadjusted. Descending onto it from above requires a
serious rate
of descent and it could be argued as unsafe.
>
> 3. Of course, roll steering would be ideal, but barring this, is there a
> better way to utilized the autopilot to fly these approaches?

Most of the dozens of KFC200s I've run into at BPPP clinics track just
fine
by turning the course arrow as commanded by the GPS. If you have a
sandel,
this is done automatically for you. Note that in strong winds, after
a 90
degree turn your ap will have to re-psych the wind; if you use APR
mode this will
be fairly rapid.
>
> 4. Would it be better to fly in heading mode, and then engage approach mode
> just prior to the FAF?

That would work. There are a lot of features in the coupling modes of
the 200.
In some cases if something isn't working right it would be really hard
to detect.
It's all analog switches driven by combinational logic. I'm sure that
some I've
seen aren't working correctly because the vast majority of them do the
problem
correctly.

Bill Hale BPPP instructor

On Apr 3, 8:18 am, Jose > wrote:
> > Would you be so kind as to explain that one? False glidescopes?
>
> The glide slope signal gets reflected off the ground, and your receiver
> hears the echo. Under some circumstances, it may interpret the echo as
> a glide slope, and falsely display a fly up or fly down indication. If
> you follow that, you will probably descend too steeply, and short of the
> runway.
>
> Jose
> --
> Get high on gasoline: fly an airplane.
> for Email, make the obvious change in the address.

Worth noting: Even without grounds, the lobes on the antennas would
cause false paths. To wit: The LOC has false nulls. Note how it
looks
as you fly around the place--swithing back and forth in a seemingly
random
way.

A place where it really matters: Jackson Hole WY. There you need to
position yourself on the loc using other navaids. Otherwise you might
run into something descending on a false LOC path.

Bill Hale BPPP instructor

My understanding is that at least the KAP 200 and 225 will not track a
glideslope (either from an LNAV+V, an LPV, or an ILS) approach when
intercepting from above, which is also my experience.

I also observed that adjusting the altitude with the autopilot up/down
switch will negate the glideslope intercept even from below while in
approach mode. Have you seen this behavior as well?

> To wit: The LOC has false nulls. Note how it looks
> as you fly around the place--swithing back and forth in a seemingly
> random way.
>
> A place where it really matters: Jackson Hole WY. There you need to
> position yourself on the loc using other navaids.

Thanks. Good point.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

On Apr 5, 8:51 pm, "Viperdoc" > wrote:
> My understanding is that at least the KAP 200 and 225 will not track a
> glideslope (either from an LNAV+V, an LPV, or an ILS) approach when
> intercepting from above, which is also my experience.
>
> I also observed that adjusting the altitude with the autopilot up/down
> switch will negate the glideslope intercept even from below while in
> approach mode. Have you seen this behavior as well?

The 200 should intercept from above if in attitude mode. Does not
know what glideslope is in use.

You can demonstrate this: but it takes a whale of a descent to set it
up.
You need to pass thru the gs center to make it couple. It's a bad
idea
in any event.

The 225 will do the same thing on ILS but not sure about GPS
approaches.

Bill Hale

My experience is that the GS has to be intercepted from below in order to
couple (also true for the 225). Also, it seems like use of the pitch toggle
while in approach mode will prevent the AP from capturing the GS.

This has happened on multiple occasions when given a late vector to
intercept, along with an altitude change, while already in NAV or HEADING
mode, with the APP mode armed. In other words, using the toggle switch for
pitch on the AP master panel while in APP mode seems to prevent the AP from
sensing and capturing the GS. This has been true for ILS as well as GPS
(LNAV/VNAV or LPV) approaches.

My only thought was to not engage the APP mode until the final altitude is
attained for GS intercept.

So, the main question is: with a King 200 AP, does the use of the pitch
toggle switch on the master panel while in APP mode negate GS tracking? How
about the CWS?
Does a switch from APP to NAV and back to APP then allow GS tracking?

On Apr 8, 6:19 am, "Viperdoc" > wrote:
> My experience is that the GS has to be intercepted from below in order to
> couple (also true for the 225). Also, it seems like use of the pitch toggle
> while in approach mode will prevent the AP from capturing the GS.
>
> This has happened on multiple occasions when given a late vector to
> intercept, along with an altitude change, while already in NAV or HEADING
> mode, with the APP mode armed. In other words, using the toggle switch for
> pitch on the AP master panel while in APP mode seems to prevent the AP from
> sensing and capturing the GS. This has been true for ILS as well as GPS
> (LNAV/VNAV or LPV) approaches.
>
> My only thought was to not engage the APP mode until the final altitude is
> attained for GS intercept.
>
> So, the main question is: with a King 200 AP, does the use of the pitch
> toggle switch on the master panel while in APP mode negate GS tracking? How
> about the CWS?
> Does a switch from APP to NAV and back to APP then allow GS tracking?

Use of the rocker does cancel GS tracking. I wonder if it also
cancels
GS intercept if operated before the GS intercepts? I'd hope not.

For example: Say you are in the alt mode before GS intercept. You
use the rocker to change altitude 100'. Shouldn't affect the
intercept.

Say you are in att mode, = not altitude. You haven't intercepted
yet.
Seems you could change the intercept attitude before the intercept.

After it couples, seems you can't use the rocker (or cws) without
decoupling the GS. The message then is that you want some other
attitude than that selected by GS couple.

I'll believe these statements are correct. I'll have to verify them
next
time I'm in a plane with a 200. The thing is full of combinational
logic--you are on your own!!

Bill Hale