[JonnyS]

We had this problem intermittently last summer, on occasion our GNC420 would flash MSG 'No altitude input being received'. The transponder would also display 'Pressure Alt FL______'.

This now seems to be a permanent thing, which is a real PITA.

I did some RV Yoga and managed to check and tighten the data cable from the Ikarus encoder, but couldn't get my hands in to check the other end of the cable in the back of the GPS. The second image below seems to suggest that the encoder is talking to the GNC420, but then I'm no avionics expert so I'm probably wrong.




Any suggestions?

[Paul_Sengupta]

I'm no expert either, but I would suspect that if you're not getting a pressure altitude reading on either the GPS or the transponder, that it's the encoder itself, or power thereto, which has gone tango uniform. I would suspect that the second photo just shows what the GNC-420 input is configured as.

[riverrock]

There are lots of ways to wire these up.
Is altitude coming into the 420 then being sent to the transponder (or the other way round?) or are they each getting their own feed?
Obvious question first - has the fuse popped on the encoder?

[JonnyS]

I think this could be a job for my borescope. I'll have another look. Strangely, I flew on Saturday and the aircraft appeared on FR24 - showing the 3727 squawk - but still no FL being shown on the trx display.