Marco Leon wrote:
Ray Andraka wrote:

Could be the encoder warm-up. The transponder won't reply mode C until
the encoder warms up. Some of them take 10 minutes or more to come up
to temperature.


Now THAT's interesting. Does anyone know if there's a bench check for
the encoder itself? I'm surprised that the avionics shop didn't suggest
the encoder as being the culprit. Is it common?

Marco


Yes, the older encoders are designed that way. They use a heater to get
the temperature to a known value to stabilize the pressure reading.
Mine is a Trans-Cal encoder, and it takes about 8 minutes on a 60 degree
day. Takes longer on a cold day. The transponder (a Narco AT165) has
an altitude readout, which shows 0 until the encoder comes alive.