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.
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.
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.
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.
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.
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
Thanks for your feedback. Hope the problem will stay away
