I have been doing some experiments logging GPS signals and accuracies. It seems there really is a monster lurking in the shadows.. GPS accuracy numbers are always stated with the caveat of "95% of the time" It made me wonder: what about the other 5% ? I fired up a BU-353 GPS puck on a laptop and monitored it with "VisualGPS" software for a period of 8 hours. The results are in the image below. The main cluster of positions is slightly Southwest of where the unit fired up. The damning data is in the "tentacles" that shoot out from the main cluster. The distance to the Northwest extreme and the Southeast extreme is ~1,600' each, from the main cluster. (See the number in the lower left of the image) This is an envelope of 3200', or over a half mile. I have seen far larger deviations, bet never took a screenshot. I am going to to a longer term study and will post the results. I started searching for Horror stories, and there they were. Random HUGE errors... Here are a few snippets: "The maximum error I ever recorded in a track, was about 600 kilometers. This was obtained two years ago with an Etrex Vista. It was working well for some time, then the position jumped 600 km to the east, where it wandered around for 8 minutes, then it jumped back." "Last week I had a similar track recorded with the GPSmap60CS. After a while with good precision, it jumped 62 km to the north, recorded 3 track points near to each other, then it jumped 84 km to the south-west where it wandered around for one minute, then it jumped back to the correct position." "While I haven't had quite such large errors, I HAVE had the GPS suddenly "think" my course had reversed itself! Also I've seen quite large groundspeeds while sitting at a stop light, speeds on the order of 600 MPH!" "That doesn't account for the observations, like Heinrich's, of errors of hundreds of kilometers. If the distribution were Gaussian I'd never expect to see errors of 1000 times sigma since the probability would be miniscule. But I've actually seen such errors a number of times. The largest error I've seen so far was a track that continued for several minutes on my eMap showing my position as over the north Pacific approaching Seattle at over 700 mph while I was actually about 1500 miles away heading south on a bike path near San Francisco at 15 mph." "In either of these cases, the position errors can be very large and are not at all Gaussian in character (e.g. an error of 1000 miles is probably just about as likely as an error of only 100 miles). Fortunately such errors are both rare and generally easy to spot" Well, "rare" and "easy to spot" certainly apply here. No many how many flights you have, all it takes is once, and it's "Bye Bye Birdie". Unless dji has an algorithm to discard ridiculously large position changes over extended lengths of time, it seems to me that we have the smoking gun.