Back in early September I flew my Mavic close to the shores of Jeju Island. Weather conditions were fair and the sky was clear. It lost signal abruptly and plummeted into the ocean .  I don't believe it was a pilot error because I had full signal at the time this happened, and there also weren't any obstacles that could of disrupted the flight. I've had DJI support review my flight records, but they came to the conclusion that it wasn't likely that it was a hardware issue as there were no indications from the flight record, and blamed the mountain for blocking the signal. This is really upsetting. How can a mountain cut the signal so abruptly? And why did the drone not return to home? I was also getting a "battery overcharge" error shortly before the disconnection, but eased off the throttle immediately. Could it be possible that it was a battery issue? Anyways, any advice would be much appreciated. Thanks in advance.

Upload the flight log (TXT file from your mobile device) to PhantomHelp and provide a link to it in this thread and we'll be in a better position to offer opinions on what happened and why. The instructions for retrieving the log and uploading it are here.

Well loosing signal should not cause AC to drop out of the sky, quite the contrary it should be a signal for AC to start RTH procedure,
But as DroneFlying said easier to give proper opinions when and if we see flight log.

DroneFlying Posted at 2017-10-25 12:45
Upload the flight log (TXT file from your mobile device) to PhantomHelp and provide a link to it in this thread and we'll be in a better position to offer opinions on what happened and why. The instructions for retrieving the log and uploading it are here.

I've found three different txt files that was modified at the time of the crash. How can I tell which one is the right one?

fans0adc3024 Posted at 2017-10-25 14:35
I've found three different txt files that was modified at the time of the crash. How can I tell which one is the right one?

If you aren't sure which is the right one then just upload and link to all three and we'll figure out which one matches your description of the flight.

DroneFlying Posted at 2017-10-25 14:38
If you aren't sure which is the right one then just upload and link to all three and we'll figure out which one matches your description of the flight.

Here it is: http://www.phantomhelp.com/LogViewer/FD3KB6C5AOX9AWWWVLKO/

dotdotcurrve Posted at 2017-10-25 14:42
Here it is: http://www.phantomhelp.com/LogViewer/FD3KB6C5AOX9AWWWVLKO/

After looking at the log I'm going to have to agree with DJI's analysis on this one. Your flight was pretty uneventful until you flew behind the mountain, and the image below shows a line between where you launched from (and presumably were located) and your Mavic at the time of last contact. That image is a little misleading because the log shows you didn't fly in a straight line but initially flew around the mountain and only eventually wound up behind it.

How can a mountain cut the signal so abruptly?

It's pretty easy for a solid obstacle like that to interfere with the signal, especially since the Mavic was almost a mile away from you when it flew behind the mountain.

And why did the drone not return to home?

It's very likely that it tried to, but your RTH height was only set to 30 meters / 100 feet, which wouldn't have been enough to clear the mountain on the return trip.

I was also getting a "battery overcharge" error shortly before the disconnection, but eased off the throttle immediately. Could it be possible that it was a battery issue?

I doubt it. The winds at that time were roughly 22 MPH near the ground and you correctly chose to fly upwind on the outbound portion of the flight. But as a result, the Mavic was having to fight the wind, which I'm guessing was why you were in Sport mode, and the large amount of power the Mavic needed to fight the wind was very likely the reason for the battery overcharge message.

Anyway, I'm sorry for your loss, but it does appear that DJI made the right call on this one.

We see this exact post almost daily now, do people not understand how land mass can block the signal - RTH kicks in (usually left at default 30m) crashes into hill... blame Dji... it's just so common and it seems NOBODY reads how to fly the Mavic or what the various functions actually do.........

TroutboyNZ Posted at 2017-10-25 16:10
We see this exact post almost daily now, do people not understand how land mass can block the signal - RTH kicks in (usually left at default 30m) crashes into hill... blame Dji... it's just so common and it seems NOBODY reads how to fly the Mavic or what the various functions actually do.........

But it's not suppose to do that

DroneFlying Posted at 2017-10-25 15:20
After looking at the log I'm going to have to agree with DJI's analysis on this one. Your flight was pretty uneventful until you flew behind the mountain, and the image below shows a line between where you launched from (and presumably were located) and your Mavic at the time of last contact. That image is a little misleading because the log shows you didn't fly in a straight line but initially flew around the mountain and only eventually wound up behind it.

How can a mountain cut the signal so abruptly?

Excellent analysis DF!

Definitely sounds his flight was doomed. That far away, low RTH, strong headwinds, and behind a mountain spells trouble.

A lot of folks should take heed this and take it as a learned lesson.

TroutboyNZ Posted at 2017-10-25 16:10
We see this exact post almost daily now, do people not understand how land mass can block the signal - RTH kicks in (usually left at default 30m) crashes into hill... blame Dji... it's just so common and it seems NOBODY reads how to fly the Mavic or what the various functions actually do.........

Couldn't agree more with you, I'm constantly scratching my head.

dotdotcurrve Posted at 2017-10-25 14:42
Here it is: http://www.phantomhelp.com/LogViewer/FD3KB6C5AOX9AWWWVLKO/

The log file does not show a home point being set so that would certainly add to the problem.

We are sorry to hear about your loss. I had checked your case, the drone behaved well during the flight, later the remote controller signal blocked by the mountain, the record ended without any sign of abnormality, please refer to the screenshot of the record below. Considering this special situation, we provided you with the best offer based on after-sales policy, hope your kindly understanding.

If Mavic encounters an obstacle when in low-altitude RTH, it should attempt to rise, if that option was enabled. But, yes, a crash is possible, if the obstacle it encounters has, for example, an overhang.

Yes, but RTH set at only 30m, it would be "stepping" forever up the slope to clear each obstacle and running out of battery in the process, I played with low altitude RTH and it's very slow trying to search for the next clear air.

Jenee 2 Posted at 2017-10-25 22:27
The log file does not show a home point being set so that would certainly add to the problem.

There was a home point set; it was done prior to the start of the last flight's log.

DroneFlying Posted at 2017-10-25 15:20
After looking at the log I'm going to have to agree with DJI's analysis on this one. Your flight was pretty uneventful until you flew behind the mountain, and the image below shows a line between where you launched from (and presumably were located) and your Mavic at the time of last contact. That image is a little misleading because the log shows you didn't fly in a straight line but initially flew around the mountain and only eventually wound up behind it.

How can a mountain cut the signal so abruptly?

I agree, this is going to happen now and then when one chooses to fly IFR.