Honeywell KFC-225 autopilot - what could cause this failure?

Hi Peter,

Looking at the kfc225 computer unit schematic, there is just one CPU
(68hc16) and no watchdog....


No watchdog? Ouch. How did they ever get this certified?

Today I've discovered that once the kfc-225 is in level flight and
holding altitude, it doesn't use the gray code data from the encoding
altimeter - it uses its own internal encoding air pressure sensor.
This rules out the altimeter problem, and narrows it down to the
computer unit, or very few other things like the input from the
altimeter subscale pot (which it still uses).


Maybe that airpressure sensor has a problem. Either EMI or maybe the
mounting location isn't as good as for the regular altimeter. Can the
KFC-225 altitude annunciator be used to see if the unit's altimeter goes
on the fritz?

The problem is that the ability of any ground based engineers to
diagnose the product is very limited, due to the really dumb firmware.


Well, they could blast it with RF in a screened room. It is standard
procedure for any med, AV or other critical gear before type cert. I
have found pretty much any EMI problem in the screen room provided I
could have the room for at least a day. But they have to test to more
than the usual 10V/m field strength.

And I still think Socata should do a courtesy fix on that oil pressure
gauge and take care of the paperwork.

Regards, Joerg

http://www.analogconsultants.com