On Tue, 26 Jun 2007 13:57:53 -0500, "Dan Luke"
wrote:


"Peter Clark" wrote:


Have you tried changing the baro in flight to some number of inches
off the real pressure to see just how far the system is mis-reading
the baro? That will tell you something.

Yes. On the ground I have set the xponder to squawk altitude and turned the
altitude preset on the KAP 140 up until it gives the "1,000 ft. before"
warning. That happens at 13,000 ft.

I'll have to go pull my wiring diagrams out since I don't recall off
the top of my head, but does the KAP140 actually get it's graycode
from the GTX, or does it get it from one of the outputs on GIA#2? Have
they tried swapping GIA#1 and GIA#2 to see if there is any difference?

The GIA2. The GIAs have been swapped and the problem stays.

Sounds like at this point they're going to have to build a harness and
ring out the graycode lines end-to-end from the GIA2 output through to
the AP computer connector individually. If both GIAs are producing
the issue and two AP computers are doing it, there's got to be
something going wrong in the harness. It's all that's left..