No idea....if you follow my whole train I have not definitively concluded anything, below is a kind of summary...
1. Compass calibration seemed pretty normal
2. 18+ satellites and solid GPS signal, since the track of the aircraft is known the Phantom had GPS the whole time.
3. Phantom drifted with no input from RC, up to 7 MPH with no input from RC....that is pretty fast....
4. The compass data shows a harmonic that increases as it approaches the powerlines, this is the only anomaly I can find.
5. The drift was not in the direction of the wind, which rules out ATTI mode...
So to me the question is why didn't the Phantom compensate for or cause the drift. It needs compass and GPS to hold position and since GPS is known good that leaves either compass or a problem with the flight controller. I would hope a compass error would cause an alert, but maybe the Phantom was just confused. I am still looking, but so far the only thing I found is the compass anomaly although it doesn't seem large enough to me to cause the drift away....but I got nothing else...maybe
@Luap will find more....
@TmoneyF,
It sounds like you are exchanging it so don't mess that up, but would be interesting to see if it flies ok somewhere else. When you get your replacement I personally would not fly at the same spot....but I am also curious if it would happen again. I might try moving mine near some powerlines to see what happens to the compass - not while flying just holding it and approaching them...not sure when I would have time for that though....