I took my Mavic Air out last week. Shortly after takeoff, it became completely unresponsive over the river and began increasing in speed as it turned back toward land, where it a hit a fence and fell straight into the river. I do not have a video of the flight, but I do have the flight log: https://app.airdata.com/share/BGDISm/GENERALNotifications.

  

The log states that there was compass interference during the flight and “Mode changed to P-GPS” notification. The warning of “Compass interference. Please move the aircraft away from potential interference source or calibrate the compass” and the loss of control of the AC was simultaneous and I had no chance of taking manual control to bring it for landing. It crashed shortly after the warning.

I have been flying the Air now for over two months and have never seen anything like this. The drone is completely lost along with my confidence in DJI’s product.

  

Questions:

1.) Why wouldn’t there be something written into DJI’s software that would prevent the drone from flying uncontrollably and faster due to a compass error? Some sort of failsafe, like when it loses connection with the controller, that would make it hover in place rather than speed up.

2.) Is this covered under warranty? I’ve only had the drone for about 2 months without any problems until now. I have a hard time believing that DJI could consider this “pilot error” as I had zero control of the AC when it crashed.

  

  

Thanks for your reading and your comments.

  

-Tyler

Hi Tyler. Thank you for reaching out and we do apologize for the incident happened to your DJI Mavic Air. I would recommend you contact our support team to start up a ticket: https://www.dji.com/support. We have the professional team who would do their best to find out the reason for the problem and then the corresponding resolution would be provided.  Please note that DJI will not provide a warranty repair for cases occurring after the expiry of the warranty period; otherwise, valid charges will apply. Thank you for your understanding. Best Regards!

If the AC does not know where it is, and doesn't know orientation (needs a working compass for that) it can't hover in place.
As to the failsafe, to hover/or RTH when it losses signal with the controller, it's already there. You can set it to go home, or hover in place. Again, only works if your compass and GPS is working correctly.

Did you check the compass readings/IMU reading before take off? IF you had any compass anomolies when taking off, or calibrating the compass, when the compass "does grab" or "clear up" from interferance, it can cause errors in positioning, and mayhem will ensue.

It may be under warranty, Did you open a ticket with DJI with the flight logs available?

Hiya,

if you like upload your flightlog using this > https://www.phantomhelp.com/LogViewer/Upload/

your upload to airdata is a private one, so no log can be downloaded from there.

cheers
JJB

Here is the uploaded flight log: https://www.phantomhelp.com/LogViewer/H36NEWE9CEZDCMYZYBNR/

Im by no means expert on this but I always calibrate my compass before each flight and making sure I'm away from magnetic interferences too, usually a grassy field will do.  Not sure if you did but would certainly recommend it in future. As for losing confidence in DJI products I'd still regard them as the best out there, not just DJI drones will crash remember.

TakeFlite Posted at 7-18 18:33
Im by no means expert on this but I always calibrate my compass before each flight and making sure I'm away from magnetic interferences too, usually a grassy field will do.  Not sure if you did but would certainly recommend it in future. As for losing confidence in DJI products I'd still regard them as the best out there, not just DJI drones will crash remember.

Some quick advice, never, ever, ever calibrate compass before every flight, my friend, NEVER.

Two things: you calibrate ONLY when crafts/device requests the calibration and second, it will typically request it if you're flying the craft about roughly 35 miles or more away from the last know flight.

tylertravels007 Posted at 7-18 13:51
Here is the uploaded flight log: https://www.phantomhelp.com/LogViewer/H36NEWE9CEZDCMYZYBNR/

Hi,

Had a look at your flightlog.

Few comments if  i may;

You started your flight using AutoTakeoff, but uses your sticks as well. Let the drone SW does the job for you, as you requested it.

Its important to do the after takeoff checks ; hover in place, yaw left and back, yaw right and back, left, right, fwd, aft and back all the time. After this check the red arrow in the app compass, check correct heading to the real life.
If checks are OKE than a happy flight.

In your case it had save your MA ; error "Compass interference. Please move the aircraft away from potential interference source or calibrate the compass." showed up in the app during autotakeoff at 4.3 secs in flight. That time your were applying 100% fwd stick, so your eyes (i guess) at the drone and not at the app.


Distance (shown in the app) from takeoff into hover must stay the same more or less 1 or 2 meter. If it increases a lot is this indicates some kind of an error. Add this to the aftertake off checks. Hard to tell in your flight as you applied fwd pitch!

During takeoff the distance went from 10.0 to 0.0 to 14.5 meters, indicates some error.

So what went wrong, some compass error so your MA did not know where it was, to wich position it should fly steady and hover without stick input.
It flew a perfect circle bow.

A good performed compass calibration can be done for each flight if you want, but it MUST be a good calibration.
Calibration does not harm in any way your drone!  But if done the wrong way, OMG  disaster is what is to be expected.

cheers
JJB

SD_Pilot Posted at 7-19 04:01
Some quick advice, never, ever, ever calibrate compass before every flight, my friend, NEVER.

Two things: you calibrate ONLY when crafts/device requests the calibration and second, it will typically request it if you're flying the craft about roughly 35 miles or more away from the last know flight.

Hi SD_Pilot,

I do not fully agree with you.

A compass calibration does not harm any drone in any way. It is just a calibration.

But when executed wrongly ( near metal, rebar in the groud, ect) it may be a succesfull calib in the app but after takeoff it will mess up your flight!

So i agree, best is to do a good calibration in a wide open green area without metal etc (watches too) and don`t do it too much.

But as said, if done in a good way it can be done for each and every flight!

cheers
JJB

Did / do you check the flight controls, inflight ie left /right/forward/back/yaw etc before you fly off over the water or did it just do its own thing after take-off?

SD_Pilot Posted at 7-19 04:01
Some quick advice, never, ever, ever calibrate compass before every flight, my friend, NEVER.

Two things: you calibrate ONLY when crafts/device requests the calibration and second, it will typically request it if you're flying the craft about roughly 35 miles or more away from the last know flight.

Rightyo I said I'm no expert. Whys that exactly

JJB* Posted at 7-19 05:58
Hi,

Had a look at your flightlog.

It's unlikely that a compass calibration is what was needed and much more likely that the compass was affected by rebar in the concrete surface he took off from. The "Please move the aircraft away from potential interference source or calibrate the compass" means that EITHER the aircraft should be moved OR that it needs a compass calibration: it doesn't mean that both are valid options but that one is needed and the aircraft doesn't know which.

You're right when you say that a compass calibration doesn't hurt anything, but a good compass calibration won't prevent problems if you try to take off from a location where there's magnetic interference, which is very likely what happened here.

TakeFlite Posted at 7-19 14:47
Rightyo I said I'm no expert. Whys that exactly

I'm going to speculate that SD_Pilot is referring to the possibility of winding up with a bad calibration, though in practice that's very unlikely. He does have a valid point, though, because once you've gotten a good calibration, there's no need to do it before every flight. If you feel better doing it then more power to you, but it's probably not necessary or helpful, and a calibration wouldn't likely have helped in this case.

JJB* Posted at 7-19 06:03
Hi SD_Pilot,

I do not fully agree with you.

I’m not certain this advice is either good or helpful.

We don't see any compass problems, we see operator problems.
A compass error is not something wrong with the compass that needs to be fixed.
It's a properly working compass that's warning that it's detected a magnetic problem in the local environment.
Calibrating the compass doesn't "fix" anything and will never fix the issue the compass is warning about.

If your compass needs calibration it will tell you, but it will first tell you to move away from Mag interference.

Yes it is now policy and SW determines you have to calibrate your drone particularly if you move some distance than you usually fly from, also it’s almost impossible with dji new drones MA mp2 etc to calibrate your drone wrong, you can try this yourself its really impossible .

If you sit your drone on a hunk of metal it will cause compass to go out of whack if you move it it returns to its normal state , so no calibration needed, if however you add or take something away from your craft then you should calibrate to insure compass values are good for what it’s working with, it will never lose calibration but stuff around it will change and that’s it .

Compass problems are caused by operator’s not by calibration .

Gimpy Posted at 7-19 15:32
I'm going to speculate that SD_Pilot is referring to the possibility of winding up with a bad calibration, though in practice that's very unlikely. He does have a valid point, though, because once you've gotten a good calibration, there's no need to do it before every flight. If you feel better doing it then more power to you, but it's probably not necessary or helpful, and a calibration wouldn't likely have helped in this case.

Ok thanks, I have just always done this and have never had a problem flying (apart from DJI app crashing today a few hundred metres over the ocean but not compass related) making sure I'm doing them well though, thanks for the info.

hallmark007 Posted at 7-19 15:49
I’m not certain this advice is either good or helpful.

We don't see any compass problems, we see operator problems.

I think my advice is good and does help people to understand the story behind compass calibration.

SD_Pilot stated that "never, ever calibrate a compass before every flight" is simply without explanation wrong.

Your explanation is almost the same as mine only other words used.

If you like to do a calibration before each flight make sure that it is a good calibration, indeed not neccesary to do but harmless to do. (IF done properly !!! )

Ofcourse a calibration does fix something (calibrated the compass system to the magn earth field at current position) , if not the case it would be a nonsense thing to do.
But it does not fix the magn interferece area in wich you calibrate, this after getting a warning in the app. As you said, move away from there and switch off and on the drone in another place.

I have no MP2, but a MA can be calibrated succesfull in the app close to the top of my car!

cheers
JJB

JJB* Posted at 7-20 01:52
I think my advice is good and does help people to understand the story behind compass calibration.

SD_Pilot stated that "never, ever calibrate a compass before every flight" is simply without explanation wrong.

Calibrating your compass has nothing to do with where you are as long as there's no spurious magnetic fields very close by).


The only reason of calibrating your compass is to measure the components of the aircraft's magnetic field so that they can be subtracted from the total measured magnetic field. Assuming no metal components like a tracking device metallic skin have been added or removed from the Mavic those compass values or measurements won't change after moving to a new location.

You can calibrate your compass as often and as many times as you like, but it is a frugal exercise and it will almost never improve anything to do with your compass. If you don’t want compass problems then environment and preflight exercise is going to help a lot more than calibration.

But aircraft belongs to the user and if he thinks calibration is helping him so be it.

you sure about it going into river? if log data is correct, at last moment of log drone was 6m higher then startpoint (20ft)/6m
when I see what height You did start, and on what height is fence on last point - I got something like 2-3m max height difference. drone should fly good over 3m over fence.
on photo I took fence as height unit. at startpoint fenceedge is 3xfence height (orange arrows, far right on photo) from water level. at endpoint (red arrows, left on photo) 4,5xfence heigh. this gives like up to 2xfence height difference.
how high can "fence unit" be? 1-1,2m max looking at photos of ppl standing near it.

KREMi Posted at 7-20 12:28
you sure about it going into river? if log data is correct, at last moment of log drone was 6m higher then startpoint (20ft)/6m
when I see what height You did start, and on what height is fence on last point - I got something like 2-3m max height difference. drone should fly good over 3m over fence.
on photo I took fence as height unit. at startpoint fenceedge is 3xfence height (orange arrows, far right on photo) from water level. at endpoint (red arrows, left on photo) 4,5xfence heigh. this gives like up to 2xfence height difference.

The AC hit the fence and went straight into the river

Gimpy Posted at 7-19 15:27
It's unlikely that a compass calibration is what was needed and much more likely that the compass was affected by rebar in the concrete surface he took off from. The "Please move the aircraft away from potential interference source or calibrate the compass" means that EITHER the aircraft should be moved OR that it needs a compass calibration: it doesn't mean that both are valid options but that one is needed and the aircraft doesn't know which.

You're right when you say that a compass calibration doesn't hurt anything, but a good compass calibration won't prevent problems if you try to take off from a location where there's magnetic interference, which is very likely what happened here.

"but a good compass calibration won't prevent problems if you try to take off from a location where there's magnetic interference, which is very likely what happened here."

Yes and no.  Assuming a good compass calibration, it depends upon amount of magnetic interference, drone's proxmity to magnetic interference, and angles of interference vs. earth's magnetic field, and drone's angle to source.  If source is strong enough, close enough, and angles conflict, then you should get a warning about magnetic interference and GO-4 app's compass / magnetic interference should show red bar (or bars in case of Mavic Pro).  


Where you can run into problems is poorly calibrated compass (or compasses) and a source of magnetic intereference.   Drone's OS can fail to detect deviations to Earth's magnetic field caused by a source magnetic interference, because drone's system during calibration compensated for transient magnetic intereference (watch, ring, eyeglasses, RC, nearby ferrous metal, etc).

SD_Pilot Posted at 7-19 04:01
Some quick advice, never, ever, ever calibrate compass before every flight, my friend, NEVER.

Two things: you calibrate ONLY when crafts/device requests the calibration and second, it will typically request it if you're flying the craft about roughly 35 miles or more away from the last know flight.

Have on numerous occasions calibrated my Mavic Pro P's two compasses repeatedly, without a requested compass calibration; and have never experienced a compass / magnetic interference problem.

IMO: Where pilots get into trouble calibrating their drone's compass is:
1) doing funky-chicken drone dance, instead of following DJI's instructions on turning and rotating drone
2) having a source of magnetic interference on them: R.C., CrystalSky, Cellphone, or ferrous metal jewelry, watch, buckle, glasses, rings, etc.  Medical metal implant in hand or arm can be a problem.
3) failing to verify if area chosen for compass calibration is free of magnetic interference

HedgeTrimmer Posted at 7-20 20:45
Have on numerous occasions calibrated my Mavic Pro P's two compasses repeatedly, without a requested compass calibration; and have never experienced a compass / magnetic interference problem.

IMO: Where pilots get into trouble calibrating their drone's compass is:

im more in favor of what SD mentioned to be honest..  if you got a good calibration set then shouldn't have to recalibrate every flight, doing it more often increases the chances of inadvertently exposing it to a bad calibration.    also i feel like everyone has their own magic min distance before should calibrate..  and who knows ...

there should be and appears are systems onboard to reduce risk the risk of bad calibrations however nothing is perfect.. i know i have gotten a bad calibration to apply before, i recalibrated on roof of my car to see if it would stop me and it didn't.. luckily didn't cause a crash or fly the wrong way on RTH .. but seems that whatever system is in place isnt perfect.

HedgeTrimmer Posted at 7-20 20:29
"but a good compass calibration won't prevent problems if you try to take off from a location where there's magnetic interference, which is very likely what happened here."

Yes and no.  Assuming a good compass calibration, it depends upon amount of magnetic interference, drone's proxmity to magnetic interference, and angles of interference vs. earth's magnetic field, and drone's angle to source.  If source is strong enough, close enough, and angles conflict, then you should get a warning about magnetic interference and GO-4 app's compass / magnetic interference should show red bar (or bars in case of Mavic Pro).  

You seem to have misunderstood how the calibration works and what exactly it's adjusting for. It doesn't and can't adjust for local phenomena like rebar in the concrete, particularly since it can't detect those once you've picked it up off the ground. Even if it did and could, the location of the rebar relative to the aircraft would be different once it was set back on the ground.

What calibration can and does compensate for is variations in the earth's magnetic field that are specific to that general location. In other words, you can calibrate as many times as you want and it still won't negate the effects of rebar. That's why the user manual says not to take off in areas with magnetic interference; it doesn't say to recalibrate and then take off from the affected location.

Your absolutely correct, but they’re are a few around here who want to continuously drag out giving ridiculous information, but never can explain why they completely waste time calibrating something that is both calibrated and doesn’t need calibration, but it’s their drone so let them continue to waste their own time and hopefully others will not pay much heed .

You explained very well it’s good and correct info particularly for beginners.

Gimpy is right and HedgeTrimmer is right too.

If people read my postings correct than it is not worth a discussion, but hope that new readers learn about this.

Doing a compass calibration means that the sofware defaults the compass setting (important that the drome is not altered in any way), than reads the earth's magnetic field on that position and if nessecarry adjust the general deviation into the compass so that North is North and not some degrees offset. Real aircraft with magetic compass (btw, obligated) often have a correction card for every 30 degrees, hard to have that on a drone. And ofcourse no need as we do not use this compass to fly towards a heading.
Compass calibration can never adjust for i.e. rebar etc. If the drone is at a different location far from where the compass was calibrated it may be done again, just to get the few degrees offset adjusted in the system. And the MA is sensitive for this, it asks often for a compass calibartion.

Having said all this : no need but absolutety no harm to do a compass calib for each flight IF (mind the bold setting) done properly; but done in an area where the compass system only 'reads' the earth magnetic field!
No metal close by, smart watches, tablets etc ect.Knowing this it is not a good idea to perform a compass calib in an congeste area full of buildings, cars etc. Yeah, but i want to fly now from here and my app shows a compass calibration message....better not!

Another thing i recently read somewhere ; the on/off button on the MA is a the bottem of the drone. If switch ON holding the drone upside down, than moving around to place on the ground may cause compass errors.  Did not test this out, but i always have my MA just above the ground (legs downwards) when switching ON.

cheers
JJB

JJB* Posted at 7-21 07:25
Gimpy is right and HedgeTrimmer is right too, not the person who thinks calibration is a kind of a calculator.

If people read my postings correct than it is not worth a discussion, but hope that new readers learn about this.

You may want to read his post again, because he isn't right in that it takes both a bad compass calibration and magnetic interference to have a problem ("Where you can run into problems is poorly calibrated compass (or compasses) and a source of magnetic intereference"); in reality, either one by itself is sufficient to create a problem. Yes, the aircraft can sometimes detect that magnetic interference is nearby and notify you of that, but not always and it isn't something that should be counted on, nor should you expect that a good calibration can overcome interference (e.g., from rebar). If a good compass calibration could overcome magnetic interference, you'd never see the message once you had a good calibration, but that's clearly not what we see.

Gimpy Posted at 7-21 07:54
You may want to read his post again, because he isn't right in that it takes both a bad compass calibration and magnetic interference to have a problem ("Where you can run into problems is poorly calibrated compass (or compasses) and a source of magnetic intereference"); in reality, either one by itself is sufficient to create a problem. Yes, the aircraft can sometimes detect that magnetic interference is nearby and notify you of that, but not always and it isn't something that should be counted on, nor should you expect that a good calibration can overcome interference (e.g., from rebar). If a good compass calibration could overcome magnetic interference, you'd never see the message once you had a good calibration, but that's clearly not what we see.

right, and should be and/or.  1 is enough to get a warning.

My point is that you have to think twice what to do when a compass calib message pops up in the app.
And if you decide to do a compass calibration again, do it in the right spot.

cheers
JJB

hallmark007 Posted at 7-21 05:56
Your absolutely correct, but they’re are a few around here who want to continuously drag out giving ridiculous information, but never can explain why they completely waste time calibrating something that is both calibrated and doesn’t need calibration, but it’s their drone so let them continue to waste their own time and hopefully others will not pay much heed .

You explained very well it’s good and correct info particularly for beginners.

Thank you very much.

JJB* Posted at 7-21 08:07
right, and should be and/or.  1 is enough to get a warning.

My point is that you have to think twice what to do when a compass calib message pops up in the app.

I completely agree and appreciate your feedback.

JJB* Posted at 7-21 07:25
Gimpy is right and HedgeTrimmer is right too.

If people read my postings correct than it is not worth a discussion, but hope that new readers learn about this.

I think there is huge misinformation being given out here regarding the calibration of compass in drone, why you should calibrate and best practice, I believe wrong and misinformation is being given out here and it leads to unnecessary and unhelpful information, yes it’s not a problem calibrating a compass but it’s wrong to tell anyone that by calibrating your compass you are somehow going to improve it , you cannot improve your compass by calibration if it’s ok in the first place and getting a warning of mag interference, calibration will not fix this in anyway .

Gimpy Posted at 7-21 04:16
You seem to have misunderstood how the calibration works and what exactly it's adjusting for. It doesn't and can't adjust for local phenomena like rebar in the concrete, particularly since it can't detect those once you've picked it up off the ground. Even if it did and could, the location of the rebar relative to the aircraft would be different once it was set back on the ground.

What calibration can and does compensate for is variations in the earth's magnetic field that are specific to that general location. In other words, you can calibrate as many times as you want and it still won't negate the effects of rebar. That's why the user manual says not to take off in areas with magnetic interference; it doesn't say to recalibrate and then take off from the affected location.

"It doesn't and can't adjust for local phenomena like rebar in the concrete, particularly since it can't detect those once you've picked it up off the ground."

"What calibration can and does compensate for is variations in the earth's magnetic field that are specific to that general location."

Your two statements conflict.   Source of magnetic interference, ferous steel (like rebar, chain link fencing, cars, buildings, metal railings) can cause variations in earth's magnetic field.  Whether magnetic interference has a magnetic field of its own or works as a shield.  Thus, compass calibration done near sufficient source of magnetic interference will result in faulty compensations for varations to earth's magnetic field.  Which is why DJI warns about making sure you are 10-meters away from sources when calibrating.

With faulty compensations to drone's compass(es), the drone is less likely to detect and warn pilot is about to take off from an area that has sufficient source of magnetic interference to cause drone flight problems.

JJB* Posted at 7-21 08:07
right, and should be and/or.  1 is enough to get a warning.

My point is that you have to think twice what to do when a compass calib message pops up in the app.

In past, when I was getting Compass calibration messages (which turned out to be bogus), I initially moved to location I knew was free of sources of magnetic interference.  Then did compass calibration.  

After wasting countless time, got to where I would do one Compass calibration for flying day, and ignore any further Compass calibration messages.

Finally, got to where I ignored Compass calibrations.  Never a flight problem.  When I got CrystalSky, which ran Android version of GO-4, the bogus Compass calibration messages stopped.

Anyway, I would suggest never calibrating compass in same spot that Compass calibration message popped up at.  Move at least 10-meters away from spot, while making sure you are not moving closer to a source of Magnetic Interference.

This is one of reasons I have suggested using a 3rd-party app on SmartPhone or SmartTablet that shows what built in compass (three axis magnetic field detectors) are detecting in regards to deviations from Earth's magnetic field.

JJB* Posted at 7-21 07:25
Gimpy is right and HedgeTrimmer is right too.

If people read my postings correct than it is not worth a discussion, but hope that new readers learn about this.

Another thing i recently read somewhere ; the on/off button on the MA is a the bottem of the drone. If switch ON holding the drone upside down, than moving around to place on the ground may cause compass errors.

Along that line...  I believe you will find when powering DJI drone up held well above ground or well away from source magnetic field is more senstive to a source of magnetic interference when it is placed on ground at take-off location.  Power DJI drone up close to source of magnetic interference, and drone is less senstive to a source.  

Gimpy Posted at 7-21 07:54
You may want to read his post again, because he isn't right in that it takes both a bad compass calibration and magnetic interference to have a problem ("Where you can run into problems is poorly calibrated compass (or compasses) and a source of magnetic intereference"); in reality, either one by itself is sufficient to create a problem. Yes, the aircraft can sometimes detect that magnetic interference is nearby and notify you of that, but not always and it isn't something that should be counted on, nor should you expect that a good calibration can overcome interference (e.g., from rebar). If a good compass calibration could overcome magnetic interference, you'd never see the message once you had a good calibration, but that's clearly not what we see.

Context...
Statement was coupled to: "Drone's OS can fail to detect deviations to Earth's magnetic field caused by a source magnetic interference, "

Nothing about what I wrote said; that properly done compass calibration can overcome sufficiently strong sources of magnetic interference.  

Distance between drone and source of magnetic interference is key part of topic.  Field strength from source is given by one of three formulas based on type of source of magnetic interference.
D = distance
1/D for low-voltage distribution (example)
1/(D*D) for transmission lines (example) also commonly used for magnets
1/(D*D*D) for domestic appliance (example)

Taking worst case 1/D, a drone 10-foot away would have 1/10th field strength it would at 1-foot away.

As someone with a bit of common sense once said .

The only purpose of compass calibration is to measure the components of the aircraft's magnetic field so that they can be subtracted from the total measured magnetic field. Rotating the three-axis magnetometers allows the aircraft's flight controller to separate the surrounding magnetic field from the magnetic field of the aircraft itself (and it doesn’t matter which way you rotate them, the manual is only a reference it’s not God) . It's able to separate them since the aircraft's magnetic field remains constant (in the frame of reference of the magnetometers) while the surrounding magnetic field rotates.

No amount of measuring will allow the aircraft's flight controller to determine the deviation or declination at a location (since it has no idea where true north is located). Declination is determined from a global declination model within the firmware. There is no way to compensate for deviation since it's unmeasurable. This should explain why taking off in areas of significant magnetic deviation will lead to unstable flight.

It is more than obvious in this case that mag interference was picked up on the ground which appears to be concrete.
There are no warnings about calibrating on PH logs, the warning clearly says move craft , no amount of calibration would have helped in this situation, so telling OP to calibrate will not in anyway help him now or in the future.
All our drones are equipped with enough information to prevent such a situation so in this case preflight would almost certainly have saved this craft .

HedgeTrimmer Posted at 7-20 20:45
Have on numerous occasions calibrated my Mavic Pro P's two compasses repeatedly, without a requested compass calibration; and have never experienced a compass / magnetic interference problem.

IMO: Where pilots get into trouble calibrating their drone's compass is:

"doing funky-chicken drone dance, instead of following DJI's instructions on turning and rotating drone"



...glad I'm doing it correctly.