Mystery Pressure Switch

Anybody know what the factory installed pressure switch is that is intalled on the pitot line behind the airspeed indicator?

The transponder docs say that it gets its “groundspeed” from the Garmin 430, but I wonder if this could be incorrect, and getting it from a switch on the pitot line. Aside from the transponder automatic ALT switching, I can’t think of anything else that would be started or stopped with the airspeed switch that is installed on my SR22 from the factory.


It’s probably wired to the gear retraction system - automatically lowers the gear for you when you slow down to approach speed. Hey, you didn’t think these things flew around at 180+KTAS with the gear still down, did you???

Could it be to activate the transponder from standby to ALT when the speed picks up, and vice versa.

The transponder doc is correct. It gets this info from the Garmin based on GPS groundspeed which switches the transponder to ALT.

A lot of brain research has been done by damaging some part and seeing what effect that has. Why don’t you disconnect it and see what stops working? Seriously, I looked in my maintenance manual, as you probably have too, and there is no indication of such a switch. Next time I have the lid off the panel I’ll see if I have one. Got to admit, I love reverse engineering. --Frank

And it can’t be the stall horn, because it doesn’t run off the pitot line. Davtron maybe?


In reply to:

Got to admit, I love reverse engineering.

Yea, me too. I wonder if Purdue offers it as a major?