Unstable flight following a compass error at take off over the ocean.

[Mario_SB]

Flight out of Viola Fields in Carpinteria, CA. This was the first flight that I experienced compass errors possibly due to railroad communications/antenna interference?? During compass errors, P3P went into ATTI mode automatically and flight was feeling really unstable. First sign of instability was at 0:55 (see uneven horizon throughout flight) then turned around at 1:18. Controller kept saying "ATTI MODE, ATTI MODE" and flight was feeling even more unstable. I was finally able to turn it around at 1:45 for a landing.

 

[Meta4]

This was the first flight that I experienced compass errors possibly due to railroad communications/antenna interference?? During compass errors, P3P went into ATTI mode automatically and flight was feeling really unstable.

There's nothing visible in the video that should have caused interference.
You were well away from any railway infrastructure.
Did you do a compass calibration before the flight? Where?
I don't see any serious instability in the video.
It just looks like your Phantom detected an inconsistency between the compass and GPS data and ignored GPS putting the Phantom into atti mode.
In atti it loses the position holding that it gets with GPS and is affected by the wind which is no big deal and quite easy to handle with a little practice.

 

[Mario_SB]

There's nothing visible in the video that should have caused interference.
You were well away from any railway infrastructure.
Did you do a compass calibration before the flight? Where?
I don't see any serious instability in the video.
It just looks like your Phantom detected an inconsistency between the compass and GPS data and ignored GPS putting the Phantom into atti mode.
In atti it loses the position holding that it gets with GPS and is affected by the wind which is no big deal and quite easy to handle with a little practice.

Thank you for the reply! I attached a few screenshots of what I'm assuming were "probable" sources of interference. The red circle shows a tall antenna next to the railroad track and the arrow points the take off and ascend direction. I'm also suspicious of interference from the oil company station on the pier (yellow circle) which communicates with the off-shore oil rigs. This was my 20th flight and my first attempt to fly over water and all my experience has been from flying over this field with no problems. Needless to say that I was not expecting my Phantom to switch over to ATTI mode or experience any compass errors on my first flight over water. I was actually pretty nervous because 1) I've never flown in ATTI mode 2) I did not know what was happening with "compass errors" flashing on the screen 3) The Phantom was flying wobbly, and it did not look stable. I had not done a compass calibration that day because I had just done one the day before from that same location. Should I have done one? I've read that you shouldn't do calibrations every time unless you've significantly change terrain or moved ~100 miles from the last point of calibration. Is this not correct??

 

[Meta4]

I attached a few screenshots of what I'm assuming were "probable" sources of interference. The red circle shows a tall antenna next to the railroad track and the arrow points the take off and ascend direction. I'm also suspicious of interference from the oil company station on the pier (yellow circle) which communicates with the off-shore oil rigs.

I suspect neither of those had any effect. You were well away from both and the kind of problem you would probably encounter if interference did happen would be a loss of signal.

I had not done a compass calibration that day because I had just done one the day before from that same location. Should I have done one? I've read that you shouldn't do calibrations every time unless you've significantly change terrain or moved ~100 miles from the last point of calibration. Is this not correct??

I asked because so many people reporting problem flights say "I always calibrate before each flight" and then it turns out they calibrated on top of a mass of steel which caused the ensuing compass problem.
Not really enough info for me to be certain of the cause or if it was just a strange one-off.
Anyway it gave you a small experience flying atti, and unless you get similar issues in future, it's probably nothing to worry about.

 

[Mario_SB]

Thanks for the info. I realize now, when coming back, that the drift to the right was indeed the wind pushing it in that direction. I really thought it was one of those "flyaways" that I hear people talking about but it was indeed ATTI mode. I have now been practicing in ATTI mode and you're right, it was an overall good learning experience. The compass issue is rather strange. :/