X-PDR

[say_speed]

How does a transponder operate? The question is, the x-pdr is independant of the pitot-static system, and its altitude readout is based on 29.92; How does it determine the altitude???

 

[JHines]

Most small aircraft have a separate blind encoder head which is like an altimeter with no display that sends the altitude signal to the transponder. It is connected to the static system. It only reports pressure altitude to ATC and their equipment converts to MSL. Is that what you're asking?

 

[say_speed]

Yes it is exactly...
I removed a couple of x-pdrs, but never noticed that it was connected to the pitot-static system.
Thank you for the answer.