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KAP 140 trouble
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 |
#2
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KAP 140 trouble
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? |
#3
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KAP 140 trouble
"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 |
#4
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KAP 140 trouble
"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/kno..._autopilot.htm |
#5
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KAP 140 trouble
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. |
#6
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KAP 140 trouble
"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 |
#7
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KAP 140 trouble
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. |
#8
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KAP 140 trouble
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.... |
#9
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KAP 140 trouble
"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 |
#10
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KAP 140 trouble
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... |
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