Every once in awhile, I try to fly a quadcopter in a place with really strange magnetic interference. Earlier this month, this happened in Scoble’s studio—I couldn’t sustain a magnetometer / compass calibration in the studio, so we had to go into Rackspace’s main work area. Today, the same thing happened at the end of Pier 14 in San Francisco.

I calibrated the Phantom 2 Vision+’s compass, waited for GPS lock, and took off. After a minute or so, the Phantom’s rear LEDs started to flash red and yellow in an alternating pattern, which signals that the magnetometer needs to be calibrated. I switched from GPS to ATT (I enabled this in Assistant by switching the Vision+ to Naza-M mode, which I prefer), landed, did a mag calibration, and took off again. The same thing happened again (I was about 10 meters up).

If you aren’t paying attention when something like this happens, it can be pretty scary. In my case, the Phantom started to drift away, even though it was in GPS mode. GPS mode with a wonky magnetometer is not reliable, which is why I like to be ready to switch into ATT at any time. If you aren’t comfortable flying in ATT, you should practice until you are. It may save your quadcopter at some point in the future!

I’m really curious as to why this particular location was doing this to my Phantom. We moved a bit further down the Embarcadero, and everything was fine. I’d love to take a second Phantom there and see if I can reproduce the issue.