I have flown my Mavic about 10 times without incident.  Today I recalibrated the compass but otherwise nothing different from past flights.  I lost connection for a few seconds when only about 1200 ft away.  As it got close it looked like it was heading for trouble so I hit cancel RTH but it wouldn't respond.  What followed was scary because my location, on a balcony, had little margin for error.  It seemed like a battle between the Mavic and my input to the control sticks.  It was spinning on its axis so forward and back was always relative to where it was in it spin.  It also kept try to go further down than the balcony.  I managed to land it on the balcony but it could easily have resulted in a bad crash.

Any suggestions as to what I did wrong or what the Mavic did wrong?  And what do I do now?

Synchronize your flight logs and ask DJI support to investigate this flight.

Sounds like a bad compass calibration.  Why did you calibrate?  Did the app ask you to do that when you started the Mavic up on the floor of the balcony?  The key to compass calibration is to NEVER calibrate if you are surrounded by metal/magnetic interference, which is what you would be doing if you calibrated on your balcony.  

If you start up your Mavic in a magnetically noisy environment, e.g. the roof/balcony of a tall building, DO NOT CALIBRATE even if the app tells you to... All that metal around you in the building is screwing around with the compasses in the Mavic, and if you calibrate there, you will be in big trouble once the Mavic has flown away from the building, because once the Mavic is not surrounded by all that metal, the compass calibration will be off, and cause the Mavic not only to have a bad compass, but could possible loose GPS as well due to this..

Go find a wide open field without any structures and calibrate the compass there, and once you've done that, you won't have to calibrate again unless you are in another location at least 500 miles from where you calibrated...

MavicUser Posted at 2017-1-20 17:56
Sounds like a bad compass calibration.  Why did you calibrate?  Did the app ask you to do that when you started the Mavic up on the floor of the balcony?  The key to compass calibration is to NEVER calibrate if you are surrounded by metal/magnetic interference, which is what you would be doing if you calibrated on your balcony.  

If you start up your Mavic in a magnetically noisy environment, e.g. the roof/balcony of a tall building, DO NOT CALIBRATE even if the app tells you to... All that metal around you in the building is screwing around with the compasses in the Mavic, and if you calibrate there, you will be in big trouble once the Mavic has flown away from the building, because once the Mavic is not surrounded by all that metal, the compass calibration will be off, and cause the Mavic not only to have a bad compass, but could possible loose GPS as well due to this..

Thank you.  That is probably the cause.  The balcony has little metal (wood railings, etc.) but there is wiring in the walls and, now that I think about it, a metal roof!  I really screwed up.