Cessna NAV II question


Well-Known Member
I own a Cessna 172 NAV II and am having an issue. The shop has looked at it twice and can't duplicate the problem.

The transponder stops reporting altitude. There are just ---- dashes where the altitude should be. At the same time the autopilot has nothing but dashes where it's altitude should be. If you hit the BARO button nothing happens. Same with the arm button. You can change between NAV/ROL but cans do anything with altitude. Then the GPS has a warning message that ALT FAILED.

it is a Cessna NAV II with a KAP140 autopilot and a king KT76C transponder. I am guessing the both have to have some part in common that has an issue causing the problem for both units.

Any ideas? I'm not paying the shop a third time todo what they have already done twice with no results.

hmm, if I remember right the autopilot has its own encoder inside the unit and separate from the transponder's encoder. What has the shop tried? I've had to pretty much demand that a shop leave it plugged in and turned on until something happened a couple of times. It seems like most shops do step A on the troubleshooting guide and when that works they say "It's good!"
They got it fixed. Both units run from the same encoder which was the bad box. $1200 later and it is fixed.