On Apr 19, 2:35 pm, "Allen" wrote:
"kevmor" wrote in message

ups.com...

I flew today to try out some more approaches with the KLN94 and the
entire time I was getting "Altitude Fail" in the MSG area, which the
manual says will display "When the altitude input becomes invalid
during operation". If I remember correctly, I think I saw when
turning it on or setting the ALT that it wasn't receiving any altitude
input, so I pushed ALT and set the altimeter to the current setting.
It kept redisplaying though... am I doing something wrong, or is it
getting a bad input possibly?

You do have either an encoding altimeter or blind encoder and it is hooked
up to the GPS and is functioning properly? You have your transponder turned
to ALT and not just to on? If the GPS is not hooked up to the encoder there
should be a way in the setup to tell it there is no encoder connected. I am
not familiar with the KLN94 but these things are pretty common to all panel
mount GPS.

The encoder lines are a big party line. They are pulled high by
the transponder usually and the altimeter pulls them low to
signify a "1". The GPS just monitors the lines--or should.
On 90B installations, you are ordered to put some diodes in the
lines so that if the 90B is turned off it won't pull the lines low and
flummox
the transponder-encoder connection.

Might also be that the encoder only gets power if the transponder
is in ALT position; haven't heard of that one. I know that on Narcos,
the encoder only got strobed in mode C--at least on really
old models.

So check your plane: You should be able to turn off the GPS
and still squak the correct altitude; you should be able to turn the
transponder off and still indicate the correct altitude on the GPS.

Bill Hale