Yesterday my Mavic just died mid-air and dropped to the ground. I am trying to analyze what happened, and so far this has been a frustrating experience.
Some background first:
I own a Mavic and a Spark. I have owned the Mavic since early December. I am not an extremely experienced drone pilot, but I do have previous extensive experience with radio controlled aircraft of different types over several decades. Up until yesterday the Mavic had performed flawlessly (more than can be said about the Spark). I have an estimated 3 hours of flying the Mavic accumulated during December, without any issues whatsoever (until yesterday).
The incident:
Took the Mavic out yesterday for some short test flights. Temperature was around +5 C, wind was low. Surroundings rural with few sources of interference. Aircraft, controller and app all at latest versions.
When I powered it up I noticed that I had forgotten to put back the SD card in the card slot since extracting some videos a few days before, so there would be no video/photo recordings. I still wanted to make some short flights to get some more practice flying it realtively low and nearby.
I took off and went up to an estimated 5 meters altitude and proceeded to fly a small circle before slowly flying a bit further away. After around one minute the Mavic was an estimated 40-50 meters away, still at around 5 meteres above take off level, flying out over a small valley. Then, without any warning the aircraft just shut down and dropped to the ground, it all happened in what seemed like a split second. The terrain at the incident position was lower than the take off point, so even if I was just 5 meters above the take off level the Mavic dropped an estimated 10 meters into a rough grassland with grass and plants and a little bit of wet snow.
Immediately after this happened I looked at the DJI GO screen and it said "aircraft disconnected". When I proceeded to move towards the accident point I could suddenly hear the motors of the Mavic engaging for a spilt second and on the DJI GO screen the "aircraft disconnected" message had disappeared and the video feed from the Mavic seemd to be restored, now showing of course only grass and snow.
After locating the aircraft and inspecting it I found it to suffer from two slightly chipped propellers, a slightly cracked right front landing gear leg and a dislocated camera gimbal (the gimbal issue was not found immediately).
After spending a long time researching how to analyze this incident I seem to have found two types of logs:
As I understand it there is a .txt file on the controller tablet. I have located this file and uploaded it here: http://www.phantomhelp.com/logviewer/BKZO7D7A6VSE62R1RSGS/
As far as I can tell it does not give much useful information other than to confirm that the aircraft just stopped transmitting after approximately one minute, which is the exact time it must have "died".
Then I have tried extracting the so-called .DAT files as decribed for example here:  https://datfile.net/DatCon/retrieveV3Dat.html
This is where I am having severe issues even locating the correct file. The files listed by the DJI Assistant software seems to have dates and times that have no relation to the dates and times of my actual flights. Even after extracting all files list by the software and unpacking them with the DJI extract utility I am unable to locate any logs of most of the flights I have made with the Mavic in December. I can find some logs, but from the time and dates and contents listed in CsvView they seem mostly to be related to times when I have powered up the Mavic indoors to check configurations, change settings and in general famliarize myself with the interface of the app. The logs of the actual flights seems to be missing as far as I can tell.
I was able to locate one log that may be from the fatal flight, but the time listed does not fit completely,and CsvView say there is no GPS data in that log so I am not able to confirm anytihng. From the time stamp it may be from a short test flight I made after the accident, after replacing the props and inspecting the aircraft. This flight was aborted quickly due to exessive camera vibrations due to a dislocated gimbal (I have since been able to fix that).
Right now I am not able to make any more test flights, due to weather conditions and short daylight hours, and I am not sure I will have time to do so for quite some days to come. In any case it is not tempting to fly the Mavic again until I have some more information about what happened, knowing that it can potentially drop out of the sky at any moment. During next weekend I may go back to the location where I have flown the Mavic during christmas, where there are areas of deep soft snow, which will greatly increase the chances of survival if this unexpected shutdown happens again.
And as noted, I am at the moment at a loss about what to do due to the appearent missing log files (or maybe I am just doing someting wrong).
Any kind of input from experienced Mavic users will be highly appreciated.
And sorry for the long first post, hope someone has the patience to read it all.

The DAT file is the only thing that might offer insight into what happened, so you'll need to retrieve it if you want someone to look into this. I don't recall hearing of a case where no DAT file was created, but I do seem to remember someone saying they had to power their Mavic off and back on again once or twice before the correct file would show up, so you should try that. And if you aren't sure which is the correct one then just include any that you think might be the right one when you select which files to retrieve.

There isn't a lot of info in that flight log to help determine the problem but the thing I find strange is that your IMU altitude got to about 16ft and never went any higher. Normally the IMU altitude and VPS altitude should be roughly the same until 30ft or 10mts when the VPS is no longer active.
You should probably contact support as it seems there may be an issue with your Mavic.

Sorry for the crash, I suggest contacting our support to start a case and send the drone in, we will help to make data analysis for this crash if the drone is under warranty, if it's a warranty case, we will get your drone repaired with no charge according to our After-sales Policy. http://www.dji.com/support

DJI Thor Posted at 2018-1-2 01:47
Sorry for the crash, I suggest contacting our support to start a case and send the drone in, we will help to make data analysis for this crash if the drone is under warranty, if it's a warranty case, we will get your drone repaired with no charge according to our After-sales Policy. http://www.dji.com/support

Thanks, Thor.
I am located in Norway, and it seems DJI does not have any service facilities here., the closest would be in the Netherlands, which would make any direct shipping quite expensive and a bit complicated.
I have contacted the local dealer from which I bought the drone here in Norway and they tell me that I can send it to them and they will handle the process.
I am at the moment a bit reluctant about what to do. The drone seems to still be operable and I am not sure how expensive it will be if I send it in and the case turns out not be be a warranty case.
What bugs me most now is that it seems the DJI Assistant software is not able to locate any logs (.DAT files) of most of my flights (see other post for more details), so I am not able check for what might have been the problem before sending it in.

Jenee 2 Posted at 2018-1-1 22:46
There isn't a lot of info in that flight log to help determine the problem but the thing I find strange is that your IMU altitude got to about 16ft and never went any higher. Normally the IMU altitude and VPS altitude should be roughly the same until 30ft or 10mts when the VPS is no longer active.
You should probably contact support as it seems there may be an issue with your Mavic.

Hi Jenee 2, Actually the flight log I posted is quite accurate and completely consistent with the actual flight. In the 1 minute that the flight lasted I never went more than approximately 5-6 meters (around 16ft) above take-off level. The VPS altitude is also correct, since this was not a flight above flat ground, I was standing on higher ground, flying out over lower ground. But I was probably never higher than around 30ft above ground, which was the case when the Mavic shut down.

DroneFlying Posted at 2018-1-1 07:57
The DAT file is the only thing that might offer insight into what happened, so you'll need to retrieve it if you want someone to look into this. I don't recall hearing of a case where no DAT file was created, but I do seem to remember someone saying they had to power their Mavic off and back on again once or twice before the correct file would show up, so you should try that. And if you aren't sure which is the correct one then just include any that you think might be the right one when you select which files to retrieve.

Thanks DroneFlying, I have been trying powering the Mavic on and off many times, and I do get a lits of logs, but there seems to be a lot of flights missing, in fact most of them.
Eventually I downloaded everything in the list (around 1 GB of data) and used the extract tool to get all the  "FLYxxx.DAT" files. I then went through every file using the CsvView tool. The result is that most of the files does not contain information that is recognizable as logs from actual flights. Most of them seems to be missing GPS information, and by the time and dates listed they appear to be logs from the occasions when I have powered on my Mavic at home to check settings etc.  Some of the logs actually have GPS data placing the drone inside my own house, so they are without doubt from such occasions. I was only able to find one .DAT file that actually contained a flight log, this was from one of my first flight, in early December. I had a number of long sucessful flights on a few dates in late December and there is not a trace to be found in the list of logs that DJI assistant provides on those dates or on aly close dates.
Also I do note that the files all seem to be numbered sequentially, FLY054.DAT, FLY055.DAT etc, but there are large "gaps" the numbering, and the gaps seems to roughly correspond to the missing flights.
The .txt log files on my tablet on the other hand contain every single flight I have made, clear and consistant.
So at the moment I am just simply not able to send in or upload any log file, since I can not find the relevent file.
I also seem to remember seeing another thread about DJI Assistant not being able to find log files on the drone, so maybe this is not just me having this problem.
I would assume that since there appear to be missing files, there could be a number of reasons for that:
1) The log files were never recorded (this seems unlikely)
2) They were later erased or overwritten, either by bug or by accident or...
3) I am just doing something wrong and therefore can not see all the files that are there
4) The logs are there but the Assistant software is not capable of finding it due to some bug.
What puzzles me most at the moment it that a lot of the times where I powered on the Mavic but did not fly seems to be there, but only one of the actual flights.
I assume these logs are stored in the internal memory of the Mavic, and not on the SD card? I have on several occasions formatted the SD card from the camera menu.

You are not alone with the DAT Problem, In my case i'm using DJI Assistant 2 1.1.6 and i'm only able to load the "Vision" Files, not the Flight data.
If you Tick the different entries in the DJI Assistant 2 for Download and decide to Download them locally you see something popup where it should say "1-Vision , 1-Flight, 2-Vision, 2-Flight ...."
but i only get "1-Vision, 2-Vision ....".
Oh, these problems where introduced with Mavic Firmware 1.3.900 or 1.3.1000, i have on the Mavic the Firmware 1.4.0100 and a downgrade to older Firmware is not possible anymore.
So we have to wait for DJI to get a DJI Assistant Version that can read all the logs.

There is a DJI Assistant 2 1.1.8 if you look in the Phantom 4 Download section with a English regio set in the site :-) But i would not install this version, as many different AV-SW solutions claim that there is Malware in this install.

So we have to wait for DJI to sort the things out and hope the best.

JensIR Posted at 2018-1-2 03:59
Thanks DroneFlying, I have been trying powering the Mavic on and off many times, and I do get a lits of logs, but there seems to be a lot of flights missing, in fact most of them.
Eventually I downloaded everything in the list (around 1 GB of data) and used the extract tool to get all the  "FLYxxx.DAT" files. I then went through every file using the CsvView tool. The result is that most of the files does not contain information that is recognizable as logs from actual flights. Most of them seems to be missing GPS information, and by the time and dates listed they appear to be logs from the occasions when I have powered on my Mavic at home to check settings etc.  Some of the logs actually have GPS data placing the drone inside my own house, so they are without doubt from such occasions. I was only able to find one .DAT file that actually contained a flight log, this was from one of my first flight, in early December. I had a number of long sucessful flights on a few dates in late December and there is not a trace to be found in the list of logs that DJI assistant provides on those dates or on aly close dates.
Also I do note that the files all seem to be numbered sequentially, FLY054.DAT, FLY055.DAT etc, but there are large "gaps" the numbering, and the gaps seems to roughly correspond to the missing flights.

Out of curiosity, which version of the DJI Assistant 2 application are you using? The only thing I can think of is that this might be related to an incompatibility between the firmware and Assistant 2 software, though that wouldn't really explain why you're still able to see some of the early non-flight files. Yes, the DAT files are stored on memory that's internal to the Mavic and not the SD that you can insert and remove for photos and video, so that wouldn't be the problem.

P.S. You're also correct that it's normal / correct for the VPS and barometric heights to differ.

DroneFlying Posted at 2018-1-2 05:22
Out of curiosity, which version of the DJI Assistant 2 application are you using? The only thing I can think of is that this might be related to an incompatibility between the firmware and Assistant 2 software, though that wouldn't really explain why you're still able to see some of the early non-flight files. Yes, the DAT files are stored on memory that's internal to the Mavic and not the SD that you can insert and remove for photos and video, so that wouldn't be the problem.

P.S. You're also correct that it's normal / correct for the VPS and barometric heights to differ.

I am using the latest version given in the downloads from DJI for the Mavic, which is 1.1.6

JensIR Posted at 2018-1-2 05:39
I am using the latest version given in the downloads from DJI for the Mavic, which is 1.1.6

I'll activate the Bat-Signal and see if Budwalker has any ideas on how to get to the right file.

I tried once more reconnecting the Mavic again today to the DJI Assitant, but the result was the same as yesterday. Except that I do notice that it seems to consistently create one new small log file for each time I power up the Mavic, but the new files of course contain nothing useful, since the Mavic is just sitting there doing nothing.  The logs from previous flights are still nowhere to be found (except for the one old file). I may try to do an actual short test flight to see if I then get a log file, but at the moment I am restricted by a combination of weather, short daylight hours and work obligations, so it will not happen for a while.

JensIR Posted at 2018-1-2 12:22
I tried once more reconnecting the Mavic again today to the DJI Assitant, but the result was the same as yesterday. Except that I do notice that it seems to consistently create one new small log file for each time I power up the Mavic, but the new files of course contain nothing useful, since the Mavic is just sitting there doing nothing.  The logs from previous flights are still nowhere to be found (except for the one old file). I may try to do an actual short test flight to see if I then get a log file, but at the moment I am restricted by a combination of weather, short daylight hours and work obligations, so it will not happen for a while.

I may try to do an actual short test flight to see if I then get a log file

That's a good idea; please let me know how it turns out. Unfortunately, I don't know what else to suggest, and I heard back from BudWalker who also couldn't recommend anything else to try, so the only other thing I can think of would be to contact DJI about it. Good luck.

JensIR Posted at 2018-1-2 03:29
Thanks, Thor.
I am located in Norway, and it seems DJI does not have any service facilities here., the closest would be in the Netherlands, which would make any direct shipping quite expensive and a bit complicated.
I have contacted the local dealer from which I bought the drone here in Norway and they tell me that I can send it to them and they will handle the process.

Since you mentioned that the drone has some damages as well as the propellers, I suggest sending it back for an overall check to ensure the stability and safety of the drone. I think you can try to contact our support first, they will guide you how to do. And you can decide to send the drone indirectly or not.
And for the flight data from the DJI Assistant 2, I saw your comment on another post, since you can access some data from the drone, please try to refresh the data and page and see if you can access them. Or you can try to reinstall the DJI Assistant 2 v1.1.6 on the Mavic website. See if it helps.  https://www.dji.com/mavic/info#downloads

I had exactly the same thing happen to my Mavic about a year ago.  It had many flawless flights on it and then suddenly lost all power and it vanished.  I received lots of help from members on the other Mavic Forum. It was nearly impossible to find because it fell from 356 feet going fast and was powerless.  After about 4 days, lucked out and found it in a tree.  All kinds of data was extracted from the Mavic and analyzed by people much smarter than me.  The experts determined that the probable cause was that I had flown my Mavic between a tall cell tower and myself at just the wrong moment.  I was about 3/4 of a mile from the 400 ft tower.  The Mavic was midway between me and the tower.  (a good distance) at 356 feet. I was flying nearly a straight line between myself and the tower.  The analyses showed the power went to zero instantly.   The tree sort of broke it's fall but the gimbal was destroyed.  After the gimbal was replaced, it checked out normal and flew with no issues.  Being curious and a little stupid, I duplicated the accident flight several times only at a slightly higher altitude.  Sure enough, it did the exact same thing again at the exact same location.  This time the power came back after a few seconds and I regained complete control.   I now make it a point to not fly a straight line between myself and any cell tower.

Hope this information keeps someone from crashing/losing their Mavic.   As a footnote, I now fly all the time with a Marco Polo tracking device and State Farm insurance.