KAP 140 trouble

[Dan Luke]

The B/K KAP 140 autopilot in my 2006 Cessna T-182T has a problem that is
baffling the avionics shop. The altitude capture/hold function does not work.
Here are the symptoms:

o All other functions work, including +/- vertical speed control.

o It will accept and correctly execute a vertical speed setting, but will
fly right through the target altitude.

o If Altitude Hold is engaged in level flight, it will not maintain
altitude.

o If Vertical Speed is engaged in level flight and set to "0", it will do
a fair job of maintaining altitude.

o According to the tech, the KAP 140 perpetually believes it is at 13,000
ft, and nothing will convince it otherwise. The unit has its own barometric
setting, independent of the G1000. However, the latest theory at the shop is
that it is a Garmin problem.


The tech's have spent a lot of time on the phone with Garmin and B/K,
listening to a lot of finger-pointing back and forth. They currently have
over 20 hours labor charged to the job--thank goodness it's warranty. I'm
able to fly the plane this weekend, but it goes back in the shop Monday.

Anybody have any ideas?

--
Dan

"You spend money to buy aggravation."
-Chinese proverb

[Peter Clark]

On Sun, 24 Jun 2007 08:49:05 -0500, "Dan Luke"
> wrote:

>The B/K KAP 140 autopilot in my 2006 Cessna T-182T has a problem that is
>baffling the avionics shop. The altitude capture/hold function does not work.
>Here are the symptoms:
>
>o All other functions work, including +/- vertical speed control.
>
>o It will accept and correctly execute a vertical speed setting, but will
>fly right through the target altitude.
>
>o If Altitude Hold is engaged in level flight, it will not maintain
>altitude.
>
>o If Vertical Speed is engaged in level flight and set to "0", it will do
>a fair job of maintaining altitude.
>
>o According to the tech, the KAP 140 perpetually believes it is at 13,000
>ft, and nothing will convince it otherwise. The unit has its own barometric
>setting, independent of the G1000. However, the latest theory at the shop is
>that it is a Garmin problem.
>
>
>The tech's have spent a lot of time on the phone with Garmin and B/K,
>listening to a lot of finger-pointing back and forth. They currently have
>over 20 hours labor charged to the job--thank goodness it's warranty. I'm
>able to fly the plane this weekend, but it goes back in the shop Monday.

Sounds like the AP computer. Did the code download come up with any
codes? The shop did hook a laptop up to the KAP140, right?

There is no connection between the G1000 and the KAP140 outside of the
GPSS and HDG outputs. Altitude modes are all internal to the KAP140
which is why it's got a static input and you need to enter the
altitude (again) and baro (again) when making changes. Is there a
blockage in the static line heading towards the KAP140? Any other
wierd readings on the primary or secondary instruments?

[Dan Luke]

"Peter Clark" wrote:

>
> Sounds like the AP computer. Did the code download come up with any
> codes?

Don't know.

> The shop did hook a laptop up to the KAP140, right?

Yes.


> There is no connection between the G1000 and the KAP140 outside of the
> GPSS and HDG outputs. Altitude modes are all internal to the KAP140
> which is why it's got a static input and you need to enter the
> altitude (again) and baro (again) when making changes.

That's what I thought. I don't see how the G1000 could have anything to do
with it.



> Is there a blockage in the static line heading towards the KAP140?

Evidently not.

> Any other wierd readings on the primary or secondary instruments?

Nope, all fine.

Thanks for your input. I'm looking for help asking questons when I see the
avionics shop guys tomorrow.

--
Dan
T-182T at BFM

[Matt Barrow[_4_]]

"Peter Clark" > wrote in message
...
>
> Sounds like the AP computer. Did the code download come up with any
> codes? The shop did hook a laptop up to the KAP140, right?
>
> There is no connection between the G1000 and the KAP140 outside of the
> GPSS and HDG outputs. Altitude modes are all internal to the KAP140
> which is why it's got a static input and you need to enter the
> altitude (again) and baro (again) when making changes. Is there a
> blockage in the static line heading towards the KAP140? Any other
> wierd readings on the primary or secondary instruments?

The King A/P's, after the KFC200, have had probems with the computers.
http://avionicswest.com/articles/know_your_autopilot.htm

[Peter Clark]

On Sun, 24 Jun 2007 10:26:53 -0500, "Dan Luke"
> wrote:


>Thanks for your input. I'm looking for help asking questons when I see the
>avionics shop guys tomorrow.

Yea, unless there's a block from the back of the T into the KAP140
(since unlike the 172 the 182 plumbs it off the back of the main
static system) there are only two things it could be, the computer, or
the pitch servo. Since it holds vertical speed modes fine, then it
seems that there's A) in fact no blockage since it wouldn't be able to
process the proper vertical speed, and B) no problem with the
pitch/trim servos. From what I can tell, they really should have just
ordered you a new KAP140 computer by now. I've not run into this
particular problem with the KAP140 but have gone through enough servos
and AP computers that this would be the only logical item left. King
sends them out without requiring the core be returned first when it's
a warranty claim. It should take about 1.5 hours to install,
including resetting the roll offsets and loading the new cert files
when the computer arrives.

Good luck.

[Dan Luke]

"Dan Luke" wrote:

>
> Anybody have any ideas?


John Jones, a fellow Cessna Pilots Ass'n member, has put me on the right
track, I believe. The autopilot receives its altitude information via Gray
code from the Garmin transponder. If a particular line is grounded, it would
hold the autopilot at 13,000 ft.

Tomorrow I'll take this information to the avionics shop and see what they
say.

--
Dan
T-182T at BFM

[Dan Luke]

> John Jones, a fellow Cessna Pilots Ass'n member, has put me on the right
> track, I believe. The autopilot receives its altitude information via Gray
> code from the Garmin transponder. If a particular line is grounded, it
> would hold the autopilot at 13,000 ft.
>
> Tomorrow I'll take this information to the avionics shop and see what they
> say.

That wasn't it. The incorrect altitude Gray code is definitely coming from
the Garmin side.

[Peter Clark]

On Tue, 26 Jun 2007 06:06:23 -0500, "Dan Luke"
> wrote:

>
>> John Jones, a fellow Cessna Pilots Ass'n member, has put me on the right
>> track, I believe. The autopilot receives its altitude information via Gray
>> code from the Garmin transponder. If a particular line is grounded, it
>> would hold the autopilot at 13,000 ft.
>>
>> Tomorrow I'll take this information to the avionics shop and see what they
>> say.
>
>That wasn't it. The incorrect altitude Gray code is definitely coming from
>the Garmin side.

If the gray code coming in from the transponder was wrong it would
hold the wrong altitude, not be unable to hold altitude....

[Matt Barrow[_4_]]

"Peter Clark" > wrote in message
...
> On Tue, 26 Jun 2007 06:06:23 -0500, "Dan Luke"
> > wrote:
>
>>
>>> John Jones, a fellow Cessna Pilots Ass'n member, has put me on the right
>>> track, I believe. The autopilot receives its altitude information via
>>> Gray
>>> code from the Garmin transponder. If a particular line is grounded, it
>>> would hold the autopilot at 13,000 ft.
>>>
>>> Tomorrow I'll take this information to the avionics shop and see what
>>> they
>>> say.
>>
>>That wasn't it. The incorrect altitude Gray code is definitely coming
>>from
>>the Garmin side.
>
> If the gray code coming in from the transponder was wrong it would
> hold the wrong altitude, not be unable to hold altitude....

As a really new (four months) G1000 owner, I must thank you for your
excellent running analysis here.

Matt
--
Matt Barrow
Performance Homes, LLC.
Cheyenne, WY

[Peter Clark]

On Tue, 26 Jun 2007 10:11:22 -0700, "Matt Barrow"
> wrote:

>
>"Peter Clark" > wrote in message
...
>> On Tue, 26 Jun 2007 06:06:23 -0500, "Dan Luke"
>> > wrote:
>>
>>>
>>>> John Jones, a fellow Cessna Pilots Ass'n member, has put me on the right
>>>> track, I believe. The autopilot receives its altitude information via
>>>> Gray
>>>> code from the Garmin transponder. If a particular line is grounded, it
>>>> would hold the autopilot at 13,000 ft.
>>>>
>>>> Tomorrow I'll take this information to the avionics shop and see what
>>>> they
>>>> say.
>>>
>>>That wasn't it. The incorrect altitude Gray code is definitely coming
>>>from
>>>the Garmin side.
>>
>> If the gray code coming in from the transponder was wrong it would
>> hold the wrong altitude, not be unable to hold altitude....
>
>As a really new (four months) G1000 owner, I must thank you for your
>excellent running analysis here.

Perhaps to complete my reasoning - the original post says it drifts
off altitude when in level flight clicking ALT. AFAIK the only time
the KAP140 cares about the altimeter setting and the preselected
altitude is when it's in a capture mode, and it uses it's internal
pressure transducer to maintain altitude. Course, wouldn't be the
first time I've been wrong about the internal workings of the box, but
it's really not that big a deal to replace it and see - it's not like
there's no known history of the KAP140 computers being problematic...

[Dan Luke]

"Peter Clark" wrote:

>
> Perhaps to complete my reasoning - the original post says it drifts
> off altitude when in level flight clicking ALT.

Sorry, that was incorrect. If ALT is selected in level flight, it will hold.
Altitude capture is the only thing not working.


> AFAIK the only time
> the KAP140 cares about the altimeter setting and the preselected
> altitude is when it's in a capture mode, and it uses it's internal
> pressure transducer to maintain altitude. Course, wouldn't be the
> first time I've been wrong about the internal workings of the box, but
> it's really not that big a deal to replace it and see - it's not like
> there's no known history of the KAP140 computers being problematic...

The KAP 140 has been swapped for a known good one. No joy.

The wiring has been checked for a ground on the Gray code lines & found to be
ok.

The tech has plugged a laptop into the system and sent various coded
altitudes to the KAP 140 and it has decoded them correctly.

Thanks a bunch for your input.

--
Dan
T-182T at BFM

[Peter Clark]

On Tue, 26 Jun 2007 13:07:02 -0500, "Dan Luke"
> wrote:

>
>"Peter Clark" wrote:
>
>>
>> Perhaps to complete my reasoning - the original post says it drifts
>> off altitude when in level flight clicking ALT.
>
>Sorry, that was incorrect. If ALT is selected in level flight, it will hold.
>Altitude capture is the only thing not working.

Ah, yep that makes a big difference...

>> AFAIK the only time
>> the KAP140 cares about the altimeter setting and the preselected
>> altitude is when it's in a capture mode, and it uses it's internal
>> pressure transducer to maintain altitude. Course, wouldn't be the
>> first time I've been wrong about the internal workings of the box, but
>> it's really not that big a deal to replace it and see - it's not like
>> there's no known history of the KAP140 computers being problematic...
>
>The KAP 140 has been swapped for a known good one. No joy.
>
>The wiring has been checked for a ground on the Gray code lines & found to be
>ok.
>
>The tech has plugged a laptop into the system and sent various coded
>altitudes to the KAP 140 and it has decoded them correctly.

Have you tried changing the baro in flight to some number of inches
off the real pressure to see just how far the system is mis-reading
the baro? That will tell you something.

I'll have to go pull my wiring diagrams out since I don't recall off
the top of my head, but does the KAP140 actually get it's graycode
from the GTX, or does it get it from one of the outputs on GIA#2? Have
they tried swapping GIA#1 and GIA#2 to see if there is any difference?

[Dan Luke]

"Peter Clark" wrote:


> Have you tried changing the baro in flight to some number of inches
> off the real pressure to see just how far the system is mis-reading
> the baro? That will tell you something.

Yes. On the ground I have set the xponder to squawk altitude and turned the
altitude preset on the KAP 140 up until it gives the "1,000 ft. before"
warning. That happens at 13,000 ft.
>
> I'll have to go pull my wiring diagrams out since I don't recall off
> the top of my head, but does the KAP140 actually get it's graycode
> from the GTX, or does it get it from one of the outputs on GIA#2? Have
> they tried swapping GIA#1 and GIA#2 to see if there is any difference?

The GIA2. The GIAs have been swapped and the problem stays.

--
Dan
T-182T at BFM

[Peter Clark]

On Tue, 26 Jun 2007 13:57:53 -0500, "Dan Luke"
> wrote:

>
>"Peter Clark" wrote:
>
>
>> Have you tried changing the baro in flight to some number of inches
>> off the real pressure to see just how far the system is mis-reading
>> the baro? That will tell you something.
>
>Yes. On the ground I have set the xponder to squawk altitude and turned the
>altitude preset on the KAP 140 up until it gives the "1,000 ft. before"
>warning. That happens at 13,000 ft.
>>
>> I'll have to go pull my wiring diagrams out since I don't recall off
>> the top of my head, but does the KAP140 actually get it's graycode
>> from the GTX, or does it get it from one of the outputs on GIA#2? Have
>> they tried swapping GIA#1 and GIA#2 to see if there is any difference?
>
>The GIA2. The GIAs have been swapped and the problem stays.

Sounds like at this point they're going to have to build a harness and
ring out the graycode lines end-to-end from the GIA2 output through to
the AP computer connector individually. If both GIAs are producing
the issue and two AP computers are doing it, there's got to be
something going wrong in the harness. It's all that's left..

[john smith]

Dan Luke wrote:
> The GIA2. The GIAs have been swapped and the problem stays.

Is the previous owner paying for all this repair time?

[Peter Clark]

On Tue, 26 Jun 2007 16:42:41 -0400, john smith > wrote:

>Dan Luke wrote:
>> The GIA2. The GIAs have been swapped and the problem stays.
>
>Is the previous owner paying for all this repair time?

The OP says it's warranty.

[Peter Clark]

On Tue, 26 Jun 2007 22:40:27 +0100, Peter >
wrote:

>
>Peter Clark > wrote
>
>>AFAIK the only time
>>the KAP140 cares about the altimeter setting and the preselected
>>altitude is when it's in a capture mode, and it uses it's internal
>>pressure transducer to maintain altitude.
>
>My KFC225 does the same, and I've had several of the baro transducers
>fail.
>
>However, reading later posts, I agree the problem must be in the gray
>code connection... this could be within the KAP140 unit though, unless
>changing that doesn't make the problem go away.

Aparantly a spare computer was swapped in and there's been no change.
Unless I've missed something here all that's left is the physical
link.

[Dan Luke]

"Peter Clark" wrote:

>>
>>The GIA2. The GIAs have been swapped and the problem stays.
>
> Sounds like at this point they're going to have to build a harness and
> ring out the graycode lines end-to-end from the GIA2 output through to
> the AP computer connector individually. If both GIAs are producing
> the issue and two AP computers are doing it, there's got to be
> something going wrong in the harness. It's all that's left..

Seems logical to me.

The tech says he is talking to Garmin about the possibility that it is a
software problem, although I cannot imagine how such a thing could appear in
only one of many identical airplanes. Faulty memory chip, maybe?

--
Dan
T-182T at BFM

[Peter Clark]

On Tue, 26 Jun 2007 17:45:51 -0500, "Dan Luke"
> wrote:

>
>"Peter Clark" wrote:
>
>>>
>>>The GIA2. The GIAs have been swapped and the problem stays.
>>
>> Sounds like at this point they're going to have to build a harness and
>> ring out the graycode lines end-to-end from the GIA2 output through to
>> the AP computer connector individually. If both GIAs are producing
>> the issue and two AP computers are doing it, there's got to be
>> something going wrong in the harness. It's all that's left..
>
>Seems logical to me.
>
>The tech says he is talking to Garmin about the possibility that it is a
>software problem, although I cannot imagine how such a thing could appear in
>only one of many identical airplanes. Faulty memory chip, maybe?

In two different GIAs and two different KAP140s? It seems rather
remote that all four componants would have a software problem that
only manifests itself on the one airframe. I think realistically it's
down to there being a short somewhere. I've not jacked into a KAP140
for quite a while so I don't remember if there's a diagnostic page
which shows the decoded input gray code, but one way for them to try
and isolate which wires on the harness are bad would be to pump the
aircraft up and see if the gray code as shown by the altimeter and
gray code as decoded by the KAP140 A) correlate and B) change with the
test set's altitude. Knowing which wires should be hot for a given
pressure will let you know which ones are bad. Have they tried
hooking up the pitot/staic testset and pumping it up?

[Dan Luke]

"Peter Clark" wrote:

> Have they tried
> hooking up the pitot/staic testset and pumping it up?

Don't know. They're getting complete schematics from Garmin for further
trouble shooting.

--
Dan
T-182T at BFM

[Peter Clark]

On Tue, 26 Jun 2007 19:43:58 -0500, "Dan Luke"
> wrote:

>
>"Peter Clark" wrote:
>
>> Have they tried
>> hooking up the pitot/staic testset and pumping it up?
>
>Don't know. They're getting complete schematics from Garmin for further
>trouble shooting.

The baseline schematics from Garmin won't neccessarily match how
Cessna has it set up. They should be looking at the wiring diagrams
on the Cessna maintenance manual CD. Have they called Cessna about
this?

[Dan Luke]

"Peter Clark" wrote:

>>Don't know. They're getting complete schematics from Garmin for further
>>trouble shooting.
>
> The baseline schematics from Garmin won't neccessarily match how
> Cessna has it set up. They should be looking at the wiring diagrams
> on the Cessna maintenance manual CD. Have they called Cessna about
> this?

That's the same thing John Jones on the CPA forum said.

I'll ask them tomorrow.

--
Dan
T-182T at BFM

[Dan Luke[_2_]]

The tech called me this afternoon and said the problem is indeed in the KAP
140 computer. How this jibes with the story I got last week that the unit
had been swapped, I don't know.

The new part will be in Tuesday. I'll report then if that truly fixes
things.

--
Dan
T-182T at BFM

[Dan Luke[_2_]]

"Peter" wrote:

>>The tech called me this afternoon and said the problem is indeed in the KAP
>>140 computer. How this jibes with the story I got last week that the unit
>>had been swapped, I don't know.
>
> Hmmm.... it is far from unknown for things that have been swapped to
> not actually having been swapped. I've had this several times.

Yep.

Back in prehistoric times when I was a tech, I did it myself. Only after I
drove 90 miles back to town did I notice the new date code on the controller I
was bringing back.

Could've happened this time.

--
Dan
T-182T at BFM

[Dan Luke[_2_]]

It was the KAP 140 computer.

Test flew it this morning and it checked out ok.

Seems like the shop could have found this out a lot sooner, seeing as how
they're a Honeywell B/K dealer & authorized warranty shop.


--
Dan
T-182T at BFM

[Peter Clark]

On Thu, 12 Jul 2007 11:11:16 -0500, "Dan Luke"
> wrote:

>
>It was the KAP 140 computer.
>
>Test flew it this morning and it checked out ok.
>
>Seems like the shop could have found this out a lot sooner, seeing as how
>they're a Honeywell B/K dealer & authorized warranty shop.

Beyond that, two different people identified it as the computer based
on your original recitation of the problem site unseen. I'd find a
new avionics shop.