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TB20 Autopilot KAP150

Yesterday in the air to fly an ILS -approach, what was happening.
As usual I checked my KAP 150 test mod on the ground, everything is perfect.
I wanted to intercept the GPS route of my GNS 530 as usual first with HDG BUG and APR.
APR mod was flashing but the airplane didn’t couple. Now I tried to couple
the ILS LOC and used the same procedure HDG BUG and APR as usual, but
again APR mod was flashing but the airplane didn’t couple. You can believe I
tried it again and again. NO COPPLEING. My GNS 530 and the SN3308 indicated
everyhting is perfect but the autopilot KAP 150 ( KC 191) didn’t copple.

In conclusion I can say the AP works fine only with HDG BUG but it doesn’t copple
by VOR/ ILS and GPS.
Has anyone an idea what it could be?
Thomas

Berlin, Germany

Make an appointment with your avionics shop, it seems NAV signals either don’t arrive or are invalid at the autopilot, or the autopilot itself needs service. Your avionics shop should have the right equipment to perform troubleshooting and repair.

JP-Avionics
EHMZ

unfortunately the AP ( Kc191) was in the shop and nobody is able to find out this temporal issue. Perhaps humidity or temperature I do not know.
Maybe the wires, perhaps the EHSI ( SN3308) or the GNS 530.
I hoped to get an idea.
Thomas

Berlin, Germany

Thomas, I thi k you need to watch this


Thomas wrote:

unfortunately the AP ( Kc191) was in the shop and nobody is able to find out this temporal issue.

If I read you correctly the problem is intermittent. In that case the problem needs to be present for the shop to find it.

You also state the autopilot was in the shop. But what about the other equipment that Jesse mentioned? Was the whole airplane in the shop? Did everything work OK in the shop?

Does the autopilot behave like this with both NAV units and both GPS (assuming you have two)? Does the CDI center as expected?

LFPT, LFPN

Very few avionics shops understand autopilots… this is not easy! In the UK for example there is only one shop (Gama) and that’s it. As for Germany, well, people get extremely passionate about that so it depends on which ex customer you speak to…

It should however not be hard to find why (basically) NAV mode doesn’t work while HDG does.

It could be the signal is getting flagged, due to the flag signal being duff, or some variation of that.

I don’t think an aircraft owner can do much on this other than a visual check of all the visible wiring and connectors.

Administrator
Shoreham EGKA, United Kingdom

Yes the airplane was in the shop and the other equipment work fine as usual.
Thanks for your interest.
Thomas

Berlin, Germany

Peter you are right. I have checked all mechanical possibilities.
I know from my own profession to explain what exactly has happened is very helpful for an expert to find out an error which is not always
present. And the discussion here is very helpful, thanks for that.
Finally I understand the NAV signal could be the reason. The questions is:
Comes this Signal direct vom GNS ( GPS / VOR) or from SANDEL (EHSI) and
goes then to the autopilot. It would be very helpful to analyse the way.
Thanks in advance
Thomas

Berlin, Germany

That depends on how your system is wired up.

I don’t know about the 3308 but when I did the installation design for my 3500 installation there was a choice of driving the autopilot from analog signals (a decoded composite NAV) which also feed an analog HSI, or driving it from the EHSI’s “FCS” output which is the “cleaner” way, not least because the autopilot works the same way regardless of whether you are tracking ILS or LPV.

Did you ever get any wiring diagrams with your plane? The Socata MM will not have anything useful re the EHSI but the shop which installed the EHSI should supply you with a copy of the work pack. You have a right to that work pack. And if/when you go to an avionics shop, that info will help them a lot.

If your installation uses the EHSI’s FCS output, and this was me, I would check the EHSI configuration has not been corrupted. But there is a lot of complication there.

Administrator
Shoreham EGKA, United Kingdom

If KAP150 doesn’t couple due to lack of NAV signal, wouldn’t it also fail to track an airway in NAV mode?

United States

If KAP150 doesn’t couple due to lack of NAV signal, wouldn’t it also fail to track an airway in NAV mode?

If by “airway” you mean the signal source is GPS and not VOR, the answer must be NO. There is no lack of signal when driven from a GPS which has a fix.

The autopilot can still uncouple for various other reasons e.g. heading flag lost (directional gyro / fluxgate issue). In that case it should fall back to ROL (wings level) mode.

Administrator
Shoreham EGKA, United Kingdom
38 Posts
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