GPS logging is not as accurate as some may think. At the rates of speeds we're flying at in addition to the erratic movements and orientation changes, often the GPS unit will not update quick enough or it may lose satellites and increase the error in position. That can turn into some strange readings which become artificially high or low. Looking at an Eagle Tree unit proves it pretty quickly when you correlate GPS velocity and airspeed from the pitot tube on a day with low wind. In a 3D plot of coordinates its also easy to see when the GPS loses it, as it starts to straight line throughout the flight path a lot, artificially cutting or elongating corners.

I'm pretty convinced that airspeed measurement by pitot tube is the best way to measure velocity, but its not perfect either as it does become influenced by air density. GPS is only really useful in my opinion if you can log air speed in parallel to verify the data.

That being said, I'd love to have seen a P-200 in a KingCat!!!

Kelly