Thanks for your feedback. Hope the problem will stay away
Fixed, at last !
The intermittent problem had soon become a constant one: it would never engage or arm APP and NAV modes.
So, the avionics workshop fixed it in two steps:
- first, they exchanged the AP computer to check if a good working unit could engage NAV and APP mode. As it didn’t work, they conclude it was coming from the cables (?) or the G1000.
- the KAP 140 gets the NAV (and HDG) information from one of the GIA63. So they did two things: a manual reset of the GIAs (they told about a button directly on the GIAs) and switched both GIAs as they are identical. The G1000 system reconfigured itself on next startup and everything worked.
So… They don’t really know if there is a a problem with the flag information from one of the GIA (which doesn’t feed anymore the AP) or if the reboot was the effective cure.
Hope it will keep on working ;)
Regards
Hello,
I exposed the problem to my maintenance by e-mail, who told me they didn’t think there was a hardware issue because the internal test was OK and no alert appeared.
I went for a new flight today.
When on the ground, I could ARM and ENGAGE Nav et Appr mode (with correct information in the CDI.)
During the first flight leg, Nav/appr mode could be engaged inconsistently… I would say 3-4 out of 5.
After one or two touch and go, on the way back to home base, it worked flawlessly. I tried all the sources in the CDI, switched the AP off then on, and managed to activate Nav or Appr mode from ROL or HDG without any problem.
When on the ground before leaving, I gave a few more try: was working normally (ARM and ENGAGE)
I must say I don’t really understand what’s going on…
I should add that when active, Nav and Appr modes are doing their job normally and don’t do anything weird.
I don’t know if it can help with troubleshooting.
What kind of inspection would you perform first ??
Best regards
Alexandre.
No problem. Let us know what was found if you want. I think it would be interesting to learn from it for all of us.
Thanks Jesse for those troubleshooting hints.
I should perform a new flight within the week to check the trouble. Then will go to my favorite shop ;-)
Best regards
Alexandre.
What might prevent AP engagement on the ground might be
These points are valid points on some aircraft, however not on C172 with G1000. I does use a Turn coordinator in the back, as the G1000 wouldn’t give the roll information in the format needed for the KAP140. In this case this is not a problem either, as the A/P functions correctly in all non radio modes.
No, you should always be able to switch it on in any mode on the ground. It might require a valid NAV or GPS signal, but that shouldn’t be a problem if your outside.
So for troubleshooting hints:
- Occured during landing / take-off
- NAV + APR doesn’t operate while receiving valid data on G1000 CDI.
- KAP-140 does not switch to NAV / NAV ARM mode, or APR, APR ARM mode.
- Full power reset doesn’t change.
- It responds the same to all CDI sources
- Power up selftest is ok.
- KAP-140 works ok in all non radio modes.
Request them to troubleshoot the NAV problem first. The approach problem might be acting up because the NAV portion doesn’t work. Ask them to take out the computer, and measure if NAV flag signal is changing between valid and invalid. This test shouldn’t be to difficult, and would give an indication if this works ok. Left and right could be tested, but is needed in my opinion, with a full left or right indication, it should go to NAV ARM mode.
To Jesse:
Can NAV/APPR mode be normally engaged when on the ground ? Or only airborne ?
Really surprising the fact I lost those modes after landing and immediate take off…
What other information would I need to describe the faulty operation ?
Yes; I wasn’t suggesting that one goes straight to an avionics shop. Just that one may be needed (or an electronically competent person if one is based where there are no good shops) to finally sort it.
I have some KAP140 stuff here because this has come up before.
It could be faulty buttons
I wouldn’t suspect them in the first place, it would be vary rare to have both failing, while the others still work. It also isn’t a problem with the common contact of the switches, as the others are still operative.
Not sure how this A/P responds to NAV flag from my memory. I think it does NAV ARM with NAV flag active, not 100% sure though.
It is likely that it won’t do approach mode, as it doesn’t operate in NAV mode either, and approach mode is using NAV mode as well.
You would only have on signal output from the G1000 to the KAP-140, for NAV this is left/right signal and flag (valid). You will always use the same wiring. However the left/right shouldn’t matter, if it is to far out (to far left or right) the KAP-140 will go to ARM mode, and waits till you intercept the NAV signal using ROL or HDG mode.
I have a huge collection of avionics manuals (on a private site) but unless you are electronically competent you will need a competent avionics installer to troubleshoot this. It may be trivial but often the wires are hard to get to, so a trivial job turns into days.
I would recommend to you generate an as good a possible fault discription. Discussing it here is a good way to find out some more information. An avionics shop could then easily pull out the KAP-140, generate signals to test and measure if all signals will arrive at the edge connector, this wouldn’t take to long. I don’t agree it would take days. It would be easy to find out if the problem is inside the KAP-140, in the wiring, or the G1000. With a good fault discription you will save yourself money.
