My autopilot has started fighting with me, and I'm afraid it's going to
win.

It's a 3-axis KAP140 in a Skyhawk SP. What it's doing is ... well, it
just starts turning.

After about an hour, it goes into a turn, unannounced. There doesn't
seem to be anything instigating it. It's usually to the left, and
always a "standard" turn.

It ignores the heading bug in HDG mode. It ignores the GPS or VOR head
in NAV mode. It also ignores the ROL mode, and the APR mode - yikes!

I don't know how far it would turn if I left it alone, because the few
times it's happened so far, I've been going somewhere.

Is this a common failure? Does anyone know what might be causing this?
Is my autopilot trying to kill me?

I just went through the exact same behavior with my King autopilot. Assuming
the flight director responds to heading bug input, then the most likely
source is the roll servo. There are four drive transistors that can burn
out, and if you are lucky this is the only problem. However, the servo motor
can also be bad, and this can be expensive as well as time consuming if the
replacement is not available. It could also be a combination of both, as was
my case.

I have the old motor sitting in front of me now- it is amazingly small
considering the forces required, and also amazingly expensive ($1,500+). I
haven't gotten my bill yet, but I anticipate it'll be in the range of
$2,5000-3,000.

Good luck.

"Brien K. Meehan" wrote:

> It's a 3-axis

Really?

"Dan Luke" > wrote in message
...
>
> "Brien K. Meehan" wrote:
>
>> It's a 3-axis
>
> Really?
Two regular axises...axeses...whatever, and an evil axis.

On 8 Sep 2006 23:51:56 -0700, "Brien K. Meehan"
> wrote:

>My autopilot has started fighting with me, and I'm afraid it's going to
>win.
>
>It's a 3-axis KAP140 in a Skyhawk SP. What it's doing is ... well, it
>just starts turning.
>
>After about an hour, it goes into a turn, unannounced. There doesn't
>seem to be anything instigating it. It's usually to the left, and
>always a "standard" turn.
>
>It ignores the heading bug in HDG mode. It ignores the GPS or VOR head
>in NAV mode. It also ignores the ROL mode, and the APR mode - yikes!
>
>I don't know how far it would turn if I left it alone, because the few
>times it's happened so far, I've been going somewhere.
>
>Is this a common failure? Does anyone know what might be causing this?
> Is my autopilot trying to kill me?

Unfortunately, it's quite common. Usually ends up being the roll
servo.

On Sat, 09 Sep 2006 11:06:07 GMT, "Viperdoc"
> wrote:

>I just went through the exact same behavior with my King autopilot. Assuming
>the flight director responds to heading bug input, then the most likely
>source is the roll servo. There are four drive transistors that can burn
>out, and if you are lucky this is the only problem. However, the servo motor
>can also be bad, and this can be expensive as well as time consuming if the
>replacement is not available. It could also be a combination of both, as was
>my case.

Skyhawks don't have a flight director ;)

At least in mine, the roll servo is one large assembly which has the
motor and all the electronics, you can't just swap out any
subcomponants - the entire unit is replaced. At least it has a gear
at the end so you don't need to deal with any of the rigging to
replace it, pop the old one out, stick the new one in, test and return
to service.

Interesting... I thought that the KAP140 was a 2-axis AP...

It sounds like your roll-servo is going south... Not bad to replace
because you just swap the old one out and the new one in..

Good luck!!

Jon Kraus
'79 Mooney 201
4443H @ UMP

Brien K. Meehan wrote:
> My autopilot has started fighting with me, and I'm afraid it's going to
> win.
>
> It's a 3-axis KAP140 in a Skyhawk SP. What it's doing is ... well, it
> just starts turning.
>
> After about an hour, it goes into a turn, unannounced. There doesn't
> seem to be anything instigating it. It's usually to the left, and
> always a "standard" turn.
>
> It ignores the heading bug in HDG mode. It ignores the GPS or VOR head
> in NAV mode. It also ignores the ROL mode, and the APR mode - yikes!
>
> I don't know how far it would turn if I left it alone, because the few
> times it's happened so far, I've been going somewhere.
>
> Is this a common failure? Does anyone know what might be causing this?
> Is my autopilot trying to kill me?
>

Yea... Gotta have someway to combat that awful Skyhawk yaw..... ;-)

Dan Luke wrote:

> "Brien K. Meehan" wrote:
>
>
>>It's a 3-axis
>
>
> Really?
>
>

I realize most Skyhawks aren't going to have a FD, but it still sounds like
a roll servo as the source of the problem, unless there's a problem getting
the heading input to the servo.

"Jon Kraus" > wrote in message
...
> Yea... Gotta have someway to combat that awful Skyhawk yaw..... ;-)
>
> Dan Luke wrote:
>
>> "Brien K. Meehan" wrote:
>>
>>
>>>It's a 3-axis
>>
>>
>> Really?


I am sure it is just 2 Axis with alt Hold !!!!!

"Jon Kraus" > wrote in message
...
> Yea... Gotta have someway to combat that awful Skyhawk yaw..... ;-)
>
> Dan Luke wrote:
>
>> "Brien K. Meehan" wrote:
>>
>>
>>>It's a 3-axis
>>
>>
>> Really?

And ............ Try Being Overweight and Really Really AFT CG, 300 Miles
from land and have the KAP140 start having spookiness to it !!! Anyway!!!!
KAP140 is a good AP I have a few hours behind it! Just always know where the
breaker is and know how to shut the thing off!! Nothing like the brand new
Cessna's with G1000 and xm radio/weather but still not worth almost $275,000
or more!

"NW_Pilot" wrote:

>>>>It's a 3-axis
>>>
>>>
>>> Really?
>
>
> I am sure it is just 2 Axis with alt Hold !!!!!

??

In article >,
Jon Kraus > wrote:

> Interesting... I thought that the KAP140 was a 2-axis AP...

KAP comes in 1-/2-and 3-axis.

"john smith" > wrote in message
...
> In article >,
> Jon Kraus > wrote:
>
>> Interesting... I thought that the KAP140 was a 2-axis AP...
>
> KAP comes in 1-/2-and 3-axis.

Direct from cessna web site!

NAV II Avionics (Bendix/King) - NAV I Avionics Plus:

KAP 140 Two-axis Autopilot with Altitude Preselect

NAV III Avionics (Garmin): Delete Standard Avionics and Add:

Fully Integrated G1000 EFIS System presented on two 10.4" high resolution
XGA displays
(PFD/MFD) - Attitude Heading Reference System (AHRS) - Solid State Air Data
Computer (ADC) - Solid State 3-Axis Magnetometer - Engine Indication and
Crew Alerting System (EICAS) - Dual Nav/Comm (16 Watt) - Dual IFR
Enroute/Approach Certified and WAAS upgradeable GPS - Fully Integrated Mode
S Transponder - Digital Audio Panel - Traffic Information System (TIS),
Terrain and Obstacle Mapping (Topographic and Relative) - Backup Airspeed,
Attitude and Altimeter - Standby Battery - KAP 140 Two-axis Autopilot with
Altitude Preselect - XM Weather and Radio.

Dan Luke wrote:
> Really?

I was going to get the 4-axis model, but they're expensive.

Viperdoc wrote:
> I realize most Skyhawks aren't going to have a FD, but it still sounds like
> a roll servo as the source of the problem, unless there's a problem getting
> the heading input to the servo.

I wouldn't think it's the servo motor itself, because the motor is
working away trying to turn the plane where it shouldn't be going. But
I have no idea.

.... but that's something to go on. :-)

On Sat, 09 Sep 2006 23:33:21 GMT, john smith > wrote:

>In article >,
> Jon Kraus > wrote:
>
>> Interesting... I thought that the KAP140 was a 2-axis AP...
>
>KAP comes in 1-/2-and 3-axis.

KAP 140 only comes in one or 2 axis, roll or pitch and roll, it
doesn't control yaw. The KFC 225 has a yaw damper connection.

Altitude preselect is not an axis.

"Brien K. Meehan" > wrote in message
oups.com...
> Dan Luke wrote:
>> Really?
>
> I was going to get the 4-axis model, but they're expensive.

Not as expensive as the time dilation model.

> KAP140 is a good AP I have a few hours behind it! Just always know where the
> breaker is and know how to shut the thing off!! Nothing like the brand new
> Cessna's with G1000 and xm radio/weather but still not worth almost $275,000
> or more!

G1000 or not, it still runs on a KAP140 autopilot...
Gerd