Hi Fuji, if PCAS provides an adequate compromise for all airspace participants then why isn't the CAA recommending its use instead of Mode-S ? If it really is low power, small, easy to use and within a reasonable price range then I agree it would be a good candidate for everybody to adopt. The only immediate thing that springs to mind is whether it contains flight vector calculations that take into consideration how each type of airspace user flies (thinking simply that in my glider it's rare for me to fly straight and level for any longer than about ten seconds as I'm constantly climbing, descending and changing heading). Would certainly be interested to understand more though.