7-25-11, i just can't let you get away with that. Your comment was way to harsh and judgemental. I was simply pointing out there may be some who don't know what their GPS speed represents and I'm sure that includes a flight instructor or two or many. And that it might be a good idea to id the "Speed" on the iFly as GS to avoid a possible error in reasoning. The pilot's I have spoken to "truely" belive the GPS speed is the speed of the airplane; but, whether it's AS of GS does't matter to them, because at some altitude AGL the difference is nill and as long as it's above stall speed we're safe. The bigger question is "where on that altitude "bell curve" do the airplane's indicated AS and GPS output speed line's cross and is the crossing point important or not..?" i.e. just before...?, 100' before..?, 1,000' before..?. And finally who really cares as long as you don't stall and don't hit the ground looking for that "nill" point...! And lets face it, at some AGL altitude it is ground speed, if you understand the GPS as much as you say you do. Should be interesting to note your GPS speed just before you touch down on any landing or in your favorite auto, and what you are going to say it represents...! BTW did you know that high air temps. or the radiated heat, like off of the rny or highway, will affect your GPS sat signal..? How much..? Enough so that my TV loses the weak Sat link-up I have on really hot day's, and always when it's full count, bottom of the 9th, in a tied ballgame... I'm sure you're smart enough to conceed that it will never get that hot in IMC while on you're GPS approach...or not..!