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My Drone Gone Missing
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KamalNor
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Yesterday I started the flight with a full battery. And at 67m altitude with 767m distance then the RC suddenly lost the signal with AC. My GO4 screen was totally greyed out and RTH is not functioning.

I managed to used RTH button on RC then I saw my Spark come towards me but it didn't stop but just passed by my/home location instead and suddenly disappeared. The RC was not functioning and I can't control the Spark manually. However, the return home history doesn't show on the flight record which I don't know why. Otherwise I can use the Fine My Drone feature.

Can somebody tell me what was actually happened? I'm really sad now. Thank you in advance.



GONE SPARKY.jpg
2018-7-15
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Mirek6
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Please upload your flight logs here: http://www.phantomhelp.com/LogViewer/Upload/ and share the link with the forum.
We can check and see if we can figure out what happened.

Mirek
2018-7-16
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Gunship9
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Is there a tall building between the pilot and the radio control aircraft at the end of the flight?
2018-7-16
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DJI Stephen
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I am sorry to know what happened to your previous flight with your DJI Spark. Since this issue happened please contact DJI support for you to know what really happened to your DJI Spark. I will post the DJI online repair request link ( www.dji.com/support ) for you to create a ticket for your Drone. Please sync the flight records of the DJI Spark using your DJI Go 4 application.
2018-7-16
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KamalNor
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Mirek6 Posted at 2018-7-16 04:58
Please upload your flight logs here: http://www.phantomhelp.com/LogViewer/Upload/ and share the link with the forum.
We can check and see if we can figure out what happened.

Thanks Mirek6 for the link. I have uploaded my flight logs http://www.phantomhelp.com/logvi ... 80VHGMUZ2QU71DFWP4/[/url]
2018-7-16
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KamalNor
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Gunship9 Posted at 2018-7-16 05:28
Is there a tall building between the pilot and the radio control aircraft at the end of the flight?

Yes but it just around 50m height and I was flying at 67m altitude. Thx
2018-7-16
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KamalNor
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DJI Stephen Posted at 2018-7-16 07:52
I am sorry to know what happened to your previous flight with your DJI Spark. Since this issue happened please contact DJI support for you to know what really happened to your DJI Spark. I will post the DJI online repair request link ( www.dji.com/support ) for you to create a ticket for your Drone. Please sync the flight records of the DJI Spark using your DJI Go 4 application.

Thanks @DJI Stephen for the link. But there are too many options until I have no idea which should I go with.
2018-7-16
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Mirek6
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KamalNor Posted at 2018-7-16 17:52
Thanks Mirek6 for the link. I have uploaded my flight logs HEREhttp://www.phantomhelp.com/logviewer/ZO80VHGMUZ2QU71DFWP4/[/url]

Kamal,

The link you provided is bad.
UPDATE:
OK - I got it - for anybody else on forum who wants to take a look the link is actually: http://www.phantomhelp.com/logviewer/ZO80VHGMUZ2QU71DFWP4/

Mirek
2018-7-16
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KamalNor
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Mirek6 Posted at 2018-7-16 19:00
Kamal,

The link you provided is bad.

Thanks Mirek. Aprreciate it a lot.
2018-7-16
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Mirek6
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KamalNor Posted at 2018-7-16 17:52
Thanks Mirek6 for the link. I have uploaded my flight logs HEREhttp://www.phantomhelp.com/logviewer/ZO80VHGMUZ2QU71DFWP4/[/url]

Kamal,

Your flight shows some abnormalities at the very beginning.
Spark can’t hold its GPS position and either drifts or GPS position which shows in logs is not 100% correct.
Home position and physical position when home point is recorded are different. Not significantly different but different nevertheless.

For 3 seconds after takeoff (between second 7 and 10) you have GPS position mismatch. This is normally sign of uncalibrated IMU or perhaps issues with getting good GPS. At your latitude it is common to have higher kP values which are measure of ionospheric disturbances which may cause inaccurate GPS readings.

Pitch and roll of your Spark are slightly (but consistently) uneven. Either slight breeze from SSW or slight IMU miscalibration. I bet on the later.

Everything seems more or less OK until 4m 40 sec when the signal breaks. You lost signal most likely because you flew behind a tall building – Spark was not in you VLOS. Since this is WiFi signal it gets very easily blocked by buildings – especially big, like the one behind which you flew.

3 seconds after signal is lost, Spark must have started failsafe RTH sequence. There is no sign that you did anything since you had no connection with Spark.

Directly in your Spark’s RTH path there is a corner of this tall building. I don’t know how tall the building is, but it looks like a very tall obstacle.

You claim that you saw Spark returning but it overshot your position and flew somewhere else. It is possible if indeed you had issues with uncalibrated IMU. Possible but highly improbable.

My bet (yes, I know that you are saying that something else happened) would be that your Spark crashed into this tall building. On return home its obstacle avoidance would have been turned off. I would look for its remains at the south corner of the building. See picture below.



This would also explain why you never regained the signal. If your Spark cleared the building successfully, your WiFi signal would reconnect within seconds.
If you, indeed, saw it going and passing over your head than DJI will need to look into this case closer. I am not sure how, since log breaks when the signal is lost.

Good luck and let us know the results of your case with DJI.

Mirek
2018-7-16
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S-e-ven
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KamalNor Posted at 2018-7-16 18:03
Yes but it just around 50m height and I was flying at 67m altitude. Thx

Does this mean you flew over and behind it and could not "see" your bird anylonger (The RC needs to "see" the AC, to stay connected. As more, as greater the distance gets?
2018-7-16
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S-e-ven
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Mirek6 Posted at 2018-7-16 21:05
Kamal,

Your flight shows some abnormalities at the very beginning.

I would even try to look at the roof.
That building has about 20 floors. With the firsts 4 or 5 of "shopping mall" height, methinks.
As it lays on the straight line between last position and HP, 67m could just not be enough to fly over it!
Do we know, how much is the ground height difference between HP and building?

Nice Job, Mirek

Lets see, if Kamal may follow your suggestion and can find something.

But that could expose himself, "Eh, have you seen a drone falling from the sky?"

"Oh, you mean that one, that chrashed into the building and fell on to the roof of the BMW (p.ex)? No, haven't seen it fallin'!
2018-7-16
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KamalNor
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Mirek6 Posted at 2018-7-16 21:05
Kamal,

Your flight shows some abnormalities at the very beginning.

Thanks a lot Marek for your time and effort with detail explanation. FYI that building on the map is my office tower. I worked with an architect firm an this tower was designed by my colleague. According to him the tower is 89.7m height and you might be right my drone could possibly hit the building during RTH mode.

But I swear I saw a drone flying over my head but it didn't stop at where I stand (Home point). Possibly somebody's else drone?.  I went to search  those locations, the last point (the same day) as well as the location marked by you (just now) but not successful. I even asked a security guard and a maintenance guy but none of them seen anything.  But may I know what is the round sign on the map?. I haven't search that area yet.

Thank you.

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2018-7-17
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Mirek6
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KamalNor Posted at 2018-7-17 00:00
Thanks a lot Marek for your time and effort with detail explanation. FYI that building on the map is my office tower. I worked with an architect firm an this tower was designed by my colleague. According to him the tower is 89.7m height and you might be right my drone could possibly hit the building during RTH mode.

But I swear I saw a drone flying over my head but it didn't stop at where I stand (Home point). Possibly somebody's else drone?.  I went to search  those locations, the last point (the same day) as well as the location marked by you (just now) but not successful. I even asked a security guard and a maintenance guy but none of them seen anything.  But may I know what is the round sign on the map?. I haven't search that area yet.

Kamal,

The round sign is an indication of where the drone was when some event occurred. Usually it is related to a warning in the log file. But not in this case. In this case it marks 3 min 49 sec into drone's normal flight in Sport mode when you were flying away from Home Point. Try to click on it on the map when you have your flight record open. It will bring you to 3 m 49 sec.

After what you said about building height, I am positive that your drone did crash in the corner of the building on its flight back during RTH. If you draw the line between your home point and a point about 30 metres beyond end of the green line which marks end of the Spark's path to SWW, you will just hit the corner of the building. I am saying 30 metres beyond end of green path because this is how much Spark needs to break when it is flying full throttle in Sport mode.

The chances that it was your drone you saw flying overhead back are slim. The only explanation could be either massive failure of your drone's navigational system or very high kP index which disturbed GPS reading. High kP indexes are known to be the root cause of GPS inaccuracies which may be measured in tens of metres.  But this is very, very, unlikely. Even if this were the main cause of your drone overshooting home point, why would you not get the RC to Spark connection back? Just too many bad coincidences to go for this scenario.

Mirek  
2018-7-17
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N2QLT
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Mirek6 Posted at 2018-7-17 04:52
Kamal,

The round sign is an indication of where the drone was when some event occurred. Usually it is related to a warning in the log file. But not in this case. In this case it marks 3 min 49 sec into drone's normal flight in Sport mode when you were flying away from Home Point. Try to click on it on the map when you have your flight record open. It will bring you to 3 m 49 sec.

Mirek,

If you are flying in an area with tall objects, shouldn't you set your RTH altitude higher than the tallest object in the flight area?
2018-7-17
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N2QLT
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Mirek6 Posted at 2018-7-17 04:52
Kamal,

The round sign is an indication of where the drone was when some event occurred. Usually it is related to a warning in the log file. But not in this case. In this case it marks 3 min 49 sec into drone's normal flight in Sport mode when you were flying away from Home Point. Try to click on it on the map when you have your flight record open. It will bring you to 3 m 49 sec.

Kp index was low on 7/14
2018-7-17
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Mirek6
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N2QLT Posted at 2018-7-17 05:26
Mirek,

If you are flying in an area with tall objects, shouldn't you set your RTH altitude higher than the tallest object in the flight area?

Yes - I do not know what altitude did Kamal set. Default is 20 metres. Most people set it to 30 metres which is high enough to avoid trees in most situations.

As for kP index - yeah, the hypothesis of missing home point because of GPS inaccuracies caused by ionospheric disturbances is far fetched and not corroborated with other facts which we see in this case. I threw it there just for completeness of analysis but I also do not believe that this is what happened. My 90% bet is on crash into the tower on return.

Mirek
2018-7-17
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N2QLT
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Mirek6 Posted at 2018-7-17 06:03
Yes - I do not know what altitude did Kamal set. Default is 20 metres. Most people set it to 30 metres which is high enough to avoid trees in most situations.

As for kP index - yeah, the hypothesis of missing home point because of GPS inaccuracies caused by ionospheric disturbances is far fetched and not corroborated with other facts which we see in this case. I threw it there just for completeness of analysis but I also do not believe that this is what happened. My 90% bet is on crash into the tower on return.

I would put my bet on your analysis.

We are probably around solar minimum right now. It's going to be interesting to see what happens maybe 6 years from now. Drones were not so popular during the peak of the current solar cycle. And it wasn't much of a peak anyway.
2018-7-17
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S-e-ven
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KamalNor Posted at 2018-7-17 00:00
Thanks a lot Marek for your time and effort with detail explanation. FYI that building on the map is my office tower. I worked with an architect firm an this tower was designed by my colleague. According to him the tower is 89.7m height and you might be right my drone could possibly hit the building during RTH mode.

But I swear I saw a drone flying over my head but it didn't stop at where I stand (Home point). Possibly somebody's else drone?.  I went to search  those locations, the last point (the same day) as well as the location marked by you (just now) but not successful. I even asked a security guard and a maintenance guy but none of them seen anything.  But may I know what is the round sign on the map?. I haven't search that area yet.

Kamal, how much is he difference in the height from starting point to the ground of the building?
I'd just try to look ON the roof for a check!

2018-7-17
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S-e-ven
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N2QLT Posted at 2018-7-17 05:26
Mirek,

If you are flying in an area with tall objects, shouldn't you set your RTH altitude higher than the tallest object in the flight area?

Or just fly higher, to begin with, yes.
2018-7-17
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62+
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Mirek6 Posted at 2018-7-16 21:05
Kamal,

Your flight shows some abnormalities at the very beginning.

Mirek

I've noticed that AC was switched to Sport mode after 2min 11.3 sec.
Traveling at max speed at multiple times. Maximum Throttle inputs.

Refer to attached graph extracted from CSV file.




2018-7-17
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Mirek6
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62+ Posted at 2018-7-17 11:32
Mirek

I've noticed that AC was switched to Sport mode after 2min 11.3 sec.

62+,

Yes - this is how Kamal was flying his drone. In Sport and full throttle forward and stop, and forward and stop (RCElevator value was switching between 1024 - neutral and 1684 - max). This, however, is OK. No problems in logs (outside of small GPS deviations I mentioned at start of the flight). The real problem occurred when he flew full speed behind the tower and lost signal. This precipitated failsafe RTH which had a tall building in its path. I am fairly sure that Spark rammed into some window or concrete at the elevation of  67 metres flying with 50 km/hour. At this speed I am not sure if you could reasonably expect to find a drone in one piece :-).

Mirek
2018-7-17
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S.J
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I think you are elligible for a new SPARK. The home point should have worked and landed at the right location.
2018-7-17
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62+
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Mirek6 Posted at 2018-7-17 12:00
62+,

Yes - this is how Kamal was flying his drone. In Sport and full throttle forward and stop, and forward and stop (RCElevator value was switching between 1024 - neutral and 1684 - max). This, however, is OK. No problems in logs (outside of small GPS deviations I mentioned at start of the flight). The real problem occurred when he flew full speed behind the tower and lost signal. This precipitated failsafe RTH which had a tall building in its path. I am fairly sure that Spark rammed into some window or concrete at the elevation of  67 metres flying with 50 km/hour. At this speed I am not sure if you could reasonably expect to find a drone in one piece :-).

Thank you Mirek,

Learning something new every day.
So the time of possible impact was when the Gyro when abnormal ?

Sorry to  Karmal and trust that DJI replace the Spark.


2018-7-17
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62+
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Sorry Mirek,

"So the time of possible impact was when the Gyro when abnormal ?

Thinking about it. It would be the time the RC lost connection with the AC.
   ….  Yes ?    or No ?
2018-7-17
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Mirek6
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62+ Posted at 2018-7-17 13:06
Sorry Mirek,

"So the time of possible impact was when the Gyro when abnormal ?

62+,

No, it wasn't like that.
Spark was flying fine, and the logs are pretty much fine (with the exception of perhaps somewhat uncalibrated IMU which shows at the beginning of the flight).

The crash happened probably less than half a minute after logs ended and communication was lost.

After RC connection was broken and logs end the following happened (assuming that Spark worked correctly):
  • Spark would break since there is no longer input from sticks. While breaking from full speed in Sport mode its inertia would carry it about 30 metres beyond the end of green line on the map.
  • Spark would than hover for 3 seconds (waiting for possible signal re-connect).
  • After 3 seconds it would start turning back in the direction of home point (start of failsafe RTH procedure which follows broken connection). This maneuver probably took about 10 seconds.
  • After that Spark started accelerating to a full speed of about 50 km/h in the straight line to home point. The problem is, in this case, it would do it at the current altitude which is 67 metres (I checked the full logs again and did notice that Kamal left RTH altitude at default of 20 metres). Directly on Spark’s return path we have corner of the tall building.

In summary – less than half a minute after logs end, Spark would have crashed into the building.
This half a minute is not in the logs since signal was broken.

Mirek
2018-7-17
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KamalNor
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S-e-ven Posted at 2018-7-17 07:27
Kamal, how much is he difference in the height from starting point to the ground of the building?
I'd just try to look ON the roof for a check!

Hi S-e-ven, not much difference I guess as it's a flat area. Well.. with a help of the security building I went to search from 10th to 15th floor (highlighted on pic) with the hope my drone stuck somewhere around the column but no joy.  

2018-7-17
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KamalNor
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Thanks again Marek with the detailed and highly logical analysis.. hats off to you man.  However it wasn't my intention to deny the fact.. but till today I strongly believe that my drone did not hit the building as I saw my drone flew over my head. My girlfriend was there with me and she can confirmed it too. I knew the buzzing sound of my lil Spark and it's 1 out of 10 possibility that the other Spark flying the same direction at the same time with mine.  The blue dot lines from the left indicates where I started to see my Spark and the end dots where I started to lose the visibility of it.



What I don't understand here, why the RTH history wasn't there in Flight record?. Otherwise I'd still can put some effort to track it by 'Find My Drone' feature. I found some cases like mine on youtube where the drone flew away during RTH mode. So it's like a common problem with Spark. Well, it could be my fault but I still submitted my case to DJI 3 days ago and still waiting for the response. And yesterday I've pre-ordered Mavic Air perhaps I won't lose it again.
2018-7-17
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S-e-ven
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KamalNor Posted at 2018-7-17 19:24
Hi S-e-ven, not much difference I guess as it's a flat area. Well.. with a help of the security building I went to search from 10th to 15th floor (highlighted on pic) with the hope my drone stuck somewhere around the column but no joy.  

[view_image]

Nice effort.
I just think, you may did your search to low ;-)

If it is 89m high, there is some structure on the roof, so the front is about 80-8x m high
Your search area started somewhere in the 40m area, which will get you just under the 67m(flightheight)  at the 15 floor, methinks.

And yes you are right, it is almost unlikely that there would be a another Spark flying your course.
Just, it may have happened. Maybe not even a Spark, 67m up, could be another small drone , Air or such.
There is a topic in here, a guy flew his spark at the ocean and saw it rising the altitude and speeding away, so he tried to get it down and back.
And he flew HIS spark in the water, because he tried to controll another one.
They are just so popular right now, they are almost everywhere.
Just saying!
2018-7-17
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djiuser_nOpLCOokxYUs
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Always make sure to set the RTH point before take off. I always double check it.
2018-7-17
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S-e-ven
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Mirek6 Posted at 2018-7-17 14:55
62+,

No, it wasn't like that.

Nice one, again, Mirek.

Would there be any different outcome, if I would tell you that the max RTH speed is "just" 36 or 38 kph?
It is using only about 3/4 of the full speed ability in RTH.
Probably to have some failsafe in RTH time calculating for "DJI recommended" (head)wind speeds.
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S-e-ven
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KamalNor Posted at 2018-7-17 20:03
Thanks again Marek with the detailed and highly logical analysis.. hats off to you man.  However it wasn't my intention to deny the fact.. but till today I strongly believe that my drone did not hit the building as I saw my drone flew over my head. My girlfriend was there with me and she can confirmed it too. I knew the buzzing sound of my lil Spark and it's 1 out of 10 possibility that the other Spark flying the same direction at the same time with mine.  The blue dot lines from the left indicates where I started to see my Spark and the end dots where I started to lose the visibility of it.

[view_image]

"What I don't understand here, why the RTH history wasn't there in Flight record?"

That is easy: The go 4 app had no connection to the Spark.

Which, in my eyes and with my own experience in disconnections (app and RC-wise), would suggest that your Spark never came back out of the RC shade of the building.
"Usually" a RC reconnects very quickly, if there is a obstacle or the distance the reason for disconnection.
Good, close to a (office?)  building, it could be also interference from other wifis, but the way back, in my understanding, would have been long enough to get your RC reconnected.

But if it indeed was a flyover, this would be a
Disconnected, RTH initiated but change to Flyaway -case

We will never know, unless you find the bird somewhere

So you had 65% battery left when disconnected, an upcoming RTH with a straightline back to HP and further on.
lets say about 50% battery left at HP, leaves 40% usuable batterylife with 36-38kph before starting to "critical battery"-landing.
Next question: How high are the buildings where your blue line gets into dots?
If it could get over all, you may have to look in the Jalan Pandan Indah area, methinks.


2018-7-17
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Mirek6
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S-e-ven Posted at 2018-7-17 23:18
Nice one, again, Mirek.

Would there be any different outcome, if I would tell you that the max RTH speed is "just" 36 or 38 kph?

62+,

No - outcome would be the same. Just the crash would have happened few seconds later.

Yes - DJI may calculate remaining battery power for safe  RTH conservatively but I am not sure why would they slow down Spark on purpose. In this case there was either no wind or very slight breeze from WWS  (pushing Spark from behind on return home).

I will double check RTH speed of my Spark next time I fly.

Mirek
2018-7-18
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Mirek6
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KamalNor Posted at 2018-7-17 20:03
Thanks again Marek with the detailed and highly logical analysis.. hats off to you man.  However it wasn't my intention to deny the fact.. but till today I strongly believe that my drone did not hit the building as I saw my drone flew over my head. My girlfriend was there with me and she can confirmed it too. I knew the buzzing sound of my lil Spark and it's 1 out of 10 possibility that the other Spark flying the same direction at the same time with mine.  The blue dot lines from the left indicates where I started to see my Spark and the end dots where I started to lose the visibility of it.

[view_image]

Kamal,

You say: "I found some cases like mine on youtube where the drone flew away during RTH mode. So it's like a common problem with Spark."

No - it is not a common problem. As a matter of fact I have never seen something like this. I have seen countless of ATTI fly-aways (pushed by the wind), I have seen some spontaneous flying in circle when sensors get confused and I have seen Sparks returning to different home than user expected because user made an error and released Spark too early and Spark updated his HP while it was already in the air and far away from the starting point.

But your case is different. You do have a strong and correct HP. Your Spark works correctly (besides perhaps small issue with IMU calibration). I have never seen Spark overshooting HP during RTH with strong GPS. I would need a log to confirm this to believe in such scenario.

Having said that - everything is possible with technology. Just chain of unfortunate coincidences required to corroborate fly-away scenario combined with absolutely logical and highly probable crash scenario is too improbable.  I bet that the drone you saw coming back was not yours.

Sorry mate - sometimes reality is hard to bear :-). I wish you good luck!

Mirek
2018-7-18
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Mirek6
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KamalNor Posted at 2018-7-17 20:03
Thanks again Marek with the detailed and highly logical analysis.. hats off to you man.  However it wasn't my intention to deny the fact.. but till today I strongly believe that my drone did not hit the building as I saw my drone flew over my head. My girlfriend was there with me and she can confirmed it too. I knew the buzzing sound of my lil Spark and it's 1 out of 10 possibility that the other Spark flying the same direction at the same time with mine.  The blue dot lines from the left indicates where I started to see my Spark and the end dots where I started to lose the visibility of it.

[view_image]

Kamal,

You say: "What I don't understand here, why the RTH history wasn't there in Flight record?"

To have RTH history you have to have RC to AC connection. There was no connection. It broke the moment your Spark went over the tall building corner.

If your Spark flew back on RTH, the connection would have been re-established within short period of time - once it cleared the building and was in VLOS again.

This total and permanent loss of connection is one of the key factors which allowed me to determine that your Spark did crash before emerging from the shadow of the tower while doing RTH.

If it was flying back over your head on a way back, it would have re-connected.

Here is why what you saw does not make sense with your Spark:
  • Spark RTH flight was on a collision course with the tower - this is a fact.
  • Spark was flying back at 67 metres of altitude since you left default setting of 20 metrese in you DJI GO - we did not Spark returning but this is normal behaviour of Spark so the huge chances are, this is what did happen.
  • Building is taller than 67 metres - this is a fact.
  • Spark has his sensors disabled on RTH from a distance higher than 100 m - we did not see it but this is normal behaviour of Spark so the huge chances are, this is what did happen.
  • If, for whatever reason (miracle? :-), Spark was able to clear the tower, you would have regained the signal - this is normal Spark behaviour.
  • If Spark did not regain the signal for whatever reason (why? signal was strong just few minutes earlier?), it would have landed on you HP becasue HP was set correctly and GPS positioning was strong - this is normal Spark behaviour.

Fascinating - eh? :-) And surely dissapointing to you :-(.
I keep my fingers crossed for your search.

Mirek
2018-7-18
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I would put a flyer at the entrance of that building, lost drone, etc., maybe it didn't crash but entered someone's apartment through an opened window and it lost the satellite connection. Then the front sensors made it stop. So it hovered until critical level of battery made it land on someone's carpet.

I didn't read the entire thread so you will forgive me if I'm babbling.
2018-7-18
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S-e-ven
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Mirek6 Posted at 2018-7-18 07:12
62+,

No - outcome would be the same. Just the crash would have happened few seconds later.

gohome.jpg



opsi, that pic above is already slowing down for obstacle avoidance switch on and landing, sry!

gohome01.jpg

Thats the speed for go home on my Spark


2018-7-18
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Mirek6
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Thank you S-e-ven and 62+,

Very interesting. I actually double checked my own flight logs and also confirmed that my RTH speed is just over 10m/s  (about 37km/h). Weird - why?

Now - I do recall RTH speed tests which somebody posted on YouTube and this forum. The guy was measuring if he can bring back Spark manually faster than automatic RTH. His conclusion was that manual was faster. I just wonder how this relates to battery life. For example if I have little battery left, do I have better chances to fly home full speed (50km/h) manually or use automatic RTH (37 km/h).
Manual would be faster but it would, conceivably, drain battery faster too.

Any thoughts?

Mirek
2018-7-18
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S-e-ven
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Mirek6 Posted at 2018-7-18 09:52
Thank you S-e-ven and 62+,

Very interesting. I actually double checked my own flight logs and also confirmed that my RTH speed is just over 10m/s  (about 37km/h). Weird - why?

I think, DJI is conservativ here.
They calculate a safe RTH, which they can guarantee in normal (recommended) windy conditions.
To have still speed "left" helps to fight wind.

And yes, I almost always cancel the RTH countdown, b/c I know by experience, I get the bird faster home in Sport, 100% full speed.
Just: If I extend that to much, there is no RTH getting it back, in case the RC disconnects!
And at least at 10% it starts landing. As we know.
2018-7-18
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Sorry but not  have the experienced to comment on this.
I would say one need to do detailed analysis of data with a number of stable variables. eg windspeed, altitude, battery level, condition of battery etc, to really test this one.

May I ask Mirek,
The heading in the CSV file "RcGyro" I do not understand.  Surly the Gyro is in the AC?

Why did the "RcGyro" value changed up and down when the AC lost connect with the RC?


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