Had a worrying happening today.
Been flying a MP now for a few months. Specialising in stills shots of marine locations. I am not a bold pilot, at all, I am anorakishly careful with the thing, do compass calibrate at every new location, always fly in GPS mode, etc etc. Never had any problems.
Today I had ‘compass redundancy’ flash up then disappear a couple of times before take-off, then when a few hundred yards away and 200’ up the thing came up with ‘compass error’ and dropped into Atti Mode. As it was quite windy this gave me a hell of a fright but I got back ok.
Checked over, recalibrate compass, tried again, same thing, went into Atti Mode.
I was standing on a large jetty, sheet piling sides and concrete top. Occurred to me that maybe there was a load of metal junk under my feet, so moved about 50 yards away and tried again. This time it behaved itself, until when bringing it back I flew over the same area again about 50’ up and it lost GPS mode again.
Reviewing the error messages later, just the compass error showed up, plus one message about wireless interference, but I also discovered I’d flipped up the sport mode switch at some stage.
There are some wifi aerials around in the area.
So, was all this to do with a load of magnetic stuff where I was taking off? Wifi aerials? Would sport mode make any difference?
This is not required and DJI actually recommend against it.
Sounds like that’s exactly what the problem was. The fact you moved and it was fine then happened again when you travelled over same area reinforces this.
Compass errors will also flag up no GPS signal error as that is flight controllers way of switching to ATTI mode.
If you get compass redundancy messages before take off that’s a sure sign something is not right. Its not redundancy in the true sense as that would require 3 magnetometers, but means 1 has high interference and it is switching to other.
You can go into sensors page on go4 and check for interference on compass 1 & 2. I’d probably do this if you ever get any more redundancy errors.
Glad you managed to keep a cool head and bring it back 
Quite worrying when it happens.
I’ll second @callum on this, no need for a compass calibrate, mines been all over Europe and the middle east and never needed one.
As long as the home point is found all is good.
You can replicate compass errors by putting the Mavic in the boot or the roof of the car after you have flown (I do this so I don’t stand on the thing).
Take a trial of Airdata and look at the error messages section, and perhaps post them here?
I’ve recently been flying from the top of a few buildings and I get magnetic interference from the reinforced concrete. The controller says ‘check app’ and I get a few conpassbrelated messages. When holding the MP around head height, the warnings go away and I’m in GPS mode. Flew after locking onto a decent amount of satellites and have had no problems.
My question is, is it safe to fly like this? I’m only taking off when there are no warnings and everything is fine.
I’ve read of a few incidents where people have said that the point of take off must’ve caused the errors later on in the flight even though everything was fine when the pilot took off?
I’ve read of stories like that as well.
I’m not entirely sure to be honest.
I’d have thought it would be fine when away from source of mag interference.
When close to it you might notice some toilet bowl effect or unexplained yaw movement as it tries to correct itself.
What your doing is not much different from physically moving to a better location.
I’d maybe just be careful when bringing it in to land.
Thanks for the interesting replies. I certainly didn’t realise that compass calibration was not needed frequently. Which piece of DJI documentation haven’t I read?!
Would it be reasonable to speculate, then, that calibrating while standing on this particular spot set the compass up in a different local magnetic field, and when I flew away from it the compass got errors? That’s effectively what happened the first couple of times - it didn’t get the errors and drop into ATTI mode until it was well away, over a wide river in fact.
Sorry, it seems the Mavic manual has been updated since I last read it.
It previously stated to only calibrate when asked to do so by app.
Here’s what it says now on page 54 of Manual
That was always the thought on calibrating too often, that it increased chance you could introduce error if calibrating close to ferrous material.
1 good calibration out in an open field was all that was needed.
I know some people who have never calibrated their Mavic.
I have done it once, i get the occasional compass error notification on my MPP so i may do it again at some point soon. I haven’t ever used Assistant 2 to calibrate sensors either, mainly because of DJI’s inability to have signed Windows drivers 
Thanks for all this, Callum. I do move around a fair bit, thinking of the 10k limit, and usually when I fire it up the page that includes calibration does appear, so I’ve assumed it’s asking me to do it!
All to do with your bearing from magnetic North changing when you travel any distance, I guess.
All really useful feedback. Great forum.
Yep according to the latest manual that’s the way to do it.
I’m now wondering if newer firmwares prompt for calibration more often.
I just can’t get my head around such a change. Going from only calibrating when prompted to every 10km. People take their drone 1000 miles on holiday and don’t have to calibrate.
10km does not seem far at all when it comes to declination.
I should really pay more attention to the instruction manual updates.
I’ve yet to find out how to do one. 
It flew OK out of the box and that’s how it’s remained.
Only did one on my P2 once when I got it out of the box.
Both the MP and P2 have been all around Europe … the MP to southern Sicily.
Yep, you were one of those people who haven’t calibrated. 