Magnetic Disturbances and P3P Compass

[Avocet]

I'm not quite sure of the best place to post this but I'll start here. Last week I did the firmware upgrade to my P3P. I ALWAYS do the firmware upgrades with no issues. I did NOT calibrate my compass after doing so, something that I consider a necessity (calibrating after upgrade).

I planned (Litchi) a flight mission to shoot some real estate footage on an island about 100 meters from the shore. I decided to calibrate the compass as a preflight item to this flight. I did get some warnings about unpaved fields nearby but they are not on the NFZ. More to the point, I did get several failed calibrations and a couple of messages about "high levels of magnetic interference ... ". I confirmed these messages by looking at the warnings stored on the device via DJI Go.

I've read the sticky on "beach" issues in calibration and although I was close (a few yards) I did do this at a distance in a gravel parking lot. It calibrated fine when I got home.

I scrubbed the mission and went home to sort out the magnetics of the situation. After a short while, I pulled up the sectional chart (attached) to see what I might find. "Magnetic Disturbances as much as 8deg. in the vicinity of ... " My flight was a mile or two away from said location. The note says "... at sea level".

Am I at risk once the bird is airborne? I balked. Can Any experience pilots or engineers shed some light on this. I really had to work hard to pack up and leave this shoot and have told myself I'm going back after some further investigation.

I am filming in and around the "Bailey's Island" VFR waypoint.
Thanks for taking a look.

 

[Meta4]

I pulled up the sectional chart (attached) to see what I might find. "Magnetic Disturbances as much as 8deg. in the vicinity of ... " My flight was a mile or two away from said location. The note says "... at sea level".

Am I at risk once the bird is airborne? I balked. Can Any experience pilots or engineers shed some light on this.

The main point to calibrating the compass is to let the compass know what magnetic and electromagnetic influences are part of the Phantom and what is from the earth's magnetic field.
I think it's unlikely that the warning on the chart was the cause of your calibration issue as magnetic variation would not trigger that sort of warning.
The most likely cause would have been steel close by.

I doubt there would be any risk if you get a good compass calibration at home and just use that.
Go back and launch and observe how your Phantom behaves.
At worst it would slowly spiral rather than hover in place - but that would be unlikely.
If it looks good 15 feet up in the air, you should be good to go for the mission.