Tl;dr
I've lost my drone. RTH hasn't worked as expected. Contacted support, so far I've got 30% discount on the drone which I consider insufficient.
Last minute of recorded flight: https://www.dropbox.com/s/87kkc8dflfkkhmz/2020_07_01_16_04_40_Cache.mp4?dl=0

I was flying my Mavic Mini over the path, slightly uphill over the forests with pretty regular trees up to 10m height. There was no wind. When I was around 400m away, I lost my signal. Normally the drone should activate the Return Home function and after a few seconds when the drone is closer and signal gets stronger I shall be able to take over the control.
I was waiting, however no reconnection happened. I've waited around 3 minutes, however the drone hasn't returned to the Home Point location.  I wasn't able to use the "Find my drone" function, as my remote didn't have a connection with the drone, so I decided to run to the area where the signal was lost.
After another minute or so, the DJI app stopped showing the drone view, it returned to home view, where I could only use the "Connect Aircraft" function, as if it was a new flight.

After around 3-4 minutes in total I was on the site where I've lost connection with the drone. I've searched the surroundings, path, trees and branches to make sure the drone hasn't crashed there, but there wasn't any sign of the drone. I kept using the "Connect Aircraft" function, so I could reconnect to my drone if I was anywhere close to it. I wasn't sure what's the range of "Connect Aircraft" function. I've returned to the Home Point location again to make sure the drone isn't there.  I've then decided to search drone in the line of Lost Connection and Home Point locations. The area was really steep and almost inaccessible, so I wasn't able to search it carefully.

After a few hours of searching I've given up, not sure what has happened.

Home point is on the path (left side image).
The last contact point is the corner (right side image)



The aircraft Relative Height during last contact was H=60,3m, whereas the RTH altitude was set to 30m. In which case it was expected to fly in a straight line to the Home Point (blue line on my drawing) after losing a signal. There is also red line which is the aircraft flight path according to the video saved in cache (https://www.dropbox.com/s/87kkc8dflfkkhmz/2020_07_01_16_04_40_Cache.mp4?dl=0).
It is noticeable that the return path (which is the right hand side on the video, marked blue on the drawing) doesn't have any obstacles which aircraft could hit. From the Home Point I was flying uphill, the return path is the valley, no obstacles.







I suspect that the RTH hasn't worked correctly. Clearly if drone would fly over the blue line and would maintain its height it then wouldn't collide with anything, in which case I would be able to take over the controls or drone would return to my position.

Since drone hasn't returned to its Home Point given the above details, I suspect that there had to be malfunction with the drone altitude measurement causing it not to maintain its altitude and crash early after RTH, even before signal was restored.

This situation made me skeptical when it comes to safety features and RTH.

Flight logs: https://www.phantomhelp.com/LogViewer/7UFQ6C1UGY6SR9O8O2WU

What are your thoughts? Have you came across into any RTH or altitude malfunction?

Won't "know" anything until the logs are posted....
watching this thread...

Flight logs soon to be uploaded.
What are your thoughts? Have you came across into any RTH or altitude malfunction?
Your flight data will probably help solve the mystery.
It only takes a minute or two.

You'll find instructions at : https://www.phantomhelp.com/logviewer/upload/
Upload your .txt file there and then post a link to the Phantomhelp report.

Uploading flight logs: https://www.phantomhelp.com/LogViewer/7UFQ6C1UGY6SR9O8O2WU

djiuser_7brXYWkAs3La Posted at 7-17 07:06
Uploading flight logs: https://www.phantomhelp.com/LogViewer/7UFQ6C1UGY6SR9O8O2WU

This situation made me skeptical when it comes to safety features and RTH.
RTH is extremely reliable.

What are your thoughts? Have you came across into any RTH or altitude malfunction?
I've never seen a case of RTH not working, but I have seen data from incidents where we cannot tell what happened.
There is usually a reason for the drone not returning even if it can't be identified.

The usual causes of drones not returning in RTH are:
1.  Obstacles or incorrect RTH height issues.
2.  Low battery situations
3.  Headwind issues

The data shows:
Your RTH path was clear of obstacles and the drone was easily high enough.
Your battery had plenty left
The wind at the drone's height was zero or very close to zero.

There's one thing that concerns me when I look deeper into the data.
The default loss of signal setting is RTH.
Have you ever changed that to one of the other settings (Descend or Hover)?

When I checked the data, it shows the Loss of Signal action as Hover but only for the first second of the data.
Were you doing anything with the Loss of Signal action before launching?

In the Flight log, I do not see there ever being a "HOME POINT SET"

That is almost always stated in the log,  yes?

Also the flight log does not show an RTH initiated........The " H " in the flight log, when you click it....it goes to 1m 5s in the time line.....150ft AGL  .6ft away.....so IF it RTH which the log does not show.....then could it have flown back to the " H " and hovered at 150 ft???  Until it ran out of power.....one would think it would auto land before shutting off under low power condition.  Your Mini might be in close proximity to the "H"

Randy

Labroides, assuming you are getting the info from the files on the Phantomhelp webpage which file contains the rth height and the loss of signal action etc? I am assuming it is one of the csv (I open those as spreadsheets) but can't see any header relating to RTH height, is the loss of signal response column FN or, if numbered, 184 in the verbose csv?

it maybe upgraded the Checkpoint if you moved your position ,,, the behaviour of DJIFLY app makes this ,,, as soon as you move some distance from the original CheckPoint it will auto upgrade,at least this is my experience .... what i mean is that maybe it returned to the original RTH or upgraded to your movement position and went there, like the friend comments above , you should be sure about the battery was enough not only to fly, you always need to confirm that the battery is enough to return too.... go to your PROFILE in DJIFLY and check the last position on the map ,, and take a look over there ,,some tree, if it still has a little bit of battery and connects you can use the FIND MY DRONE which will produce some small noises , i am always assuming that you really pressed RTH,maybe you did it but the system didn't receive the command because the signal fault .. good luck

Digging into your data again .. you took off without GPS so the drone had not recorded a homepoint.
It wasn't until 0:58.4 that the drone was able to record it's home point.
You had only flown a little way but the drone will have drifted without GPS position holding ability.

The homepoint was recorded when GPS position data was acquired at 41.32722        22.92245
This is the place the drone would have returned to on losing signal (if the loss of signal action was still set to RTH).
It's in vegetation off the road as you can see in the Phantomhelp report.

Sean-newbie Posted at 7-17 10:24
Labroides, assuming you are getting the info from the files on the Phantomhelp webpage which file contains the rth height and the loss of signal action etc? I am assuming it is one of the csv (I open those as spreadsheets) but can't see any header relating to RTH height, is the loss of signal response column FN or, if numbered, 184 in the verbose csv?

In the Verbose CSV
BG  = MC_PARAM.failSafeAction
GW   = HOME.goHomeHeight [m]

rwynant V1 Posted at 7-17 10:10
In the Flight log, I do not see there ever being a "HOME POINT SET"

That is almost always stated in the log,  yes?

In the Flight log, I do not see there ever being a "HOME POINT SET"
The home point was set at 0:58.4

i am always assuming that you really pressed RTH,maybe you did it but the system didn't receive the command because the signal fault

I didn't. I've lost signal and relied on RTH action being triggered automatically. It always worked fine.


it maybe upgraded the Checkpoint if you moved your position ,,, the behaviour of DJIFLY app makes this ,,, as soon as you move some distance from the original CheckPoin

I've moved from Home Point (towards last contact point) after ~3 minutes from losing a signal and since that moment, signal was never restored.
At this point it was clear that something went wrong and drone is not returning. Drone wasn't far away, it was only 400m, so the RTH would bring it in about a minute I guess.


Have you ever changed that to one of the other settings (Descend or Hover)?
When I checked the data, it shows the Loss of Signal action as Hover but only for the first second of the data.
Were you doing anything with the Loss of Signal action before launching?

I've always had the Loss of Signal action set to RTH and never changed that to anything else. I am not sure why logs indicate Hover in the: `MC_PARAM.failSafeAction` early in the logs.


The homepoint was recorded when GPS position data was acquired at 41.32722        22.92245
This is the place the drone would have returned to on losing signal (if the loss of signal action was still set to RTH).
It's in vegetation off the road as you can see in the Phantomhelp report.


That GPS position was almost my position as a pilot. In fact it's not off the road too much if any. The Google Maps road mark drifted from reality, it is visible on the sat maps where you can see the area without trees.



I was standing there for about 3 minutes after losing a signal and there were no signs of drone which normally I could hear even if it's far away.
I've searched that area carefully and no signs of drone.

It's still a mystery to me what has happened.

did you check at the video if some bird attacked it ?

I haven't noticed any birds during flight and in that area.
I've got reply from DJI, due to missing flight logs they can't analyze the situation and still assume that everything with drone worked fine.
It means that all cases where signal was lost will always be the ones where customer is at fault.
I wish these drones has GPS locators, so it's possible to track them more easily if signal gets lost.
Anyway, thanks for all your help. It seems I need to buy a new drone...