On Thursday, May 5, 2016 at 11:17:11 AM UTC-7, wrote:
Here at Chicago Glider Club we have the dubious distinction of flying right under the approach path into Midway airport. I have looked at SouthWest planes coming through from all angles, including head-on. Flying with a C-mode transponder helps a lot, Approach will guide the big iron around us although I'm sometimes wondering about the spacing.
My PFlarm will indicate through the FlarmView display a blue dot around my position that is blinking ONLY when a SW or bigger commercial plane (equipped with TCAS?) is coming through. Could there be a connection such that the transponder when interrogated by a TCAS responds in a way that is picked up by PFlarm? What else might the blue blinking dot mean?
Please enlighten me.
Herb, J7

that is a mode C or mode S transponder it is non directional and as it gets closer the circle should get smaller. Blue means it is above you.

Richard
www.craggyaero.com