I watched a video where a DJI drone, possibly a Mini 2 is being forced landing in the sea,
because that it thinks it's at negative 409 meters height and it's 759 meters far from the homepoint.
From the video it looks like the drone is not higher than 150 meters, so 32 percent battery should be enough to fly 759 meters back to the homepoint.
What's wrong with this drone ? How can we avoid having a similar situation with our drones ?

How can anyone diagnose the problem with that drone when you are not even the pilot and there is no flight log?
The video is too fragmented to be of any use other than to suggest the pilot flew too high, possibly too far and all in probably unsuitable conditions.

That said a negative height of 400m, let alone -640m, is highly suspect unless the drone's firmware has been hacked to allow it to break 500m.
If it isn't a malfunction of the drone the only way that I can think that, at apparent height, the indicated height could be so negative is if the drone was well above 500m and then lost contact. Then, after a while, regain contact.

At those heights it is quite likely the drone encountered

In such circumstances I have had a Mavic mini , a Mini 2 and a Mavic 2 Pro start a new .txt flight log on reconnection and, going by the flight log, have a significant negative height at landing. I do not rememebr what the apps showed, I watch the drone not the screen.

As for avoiding a 'repetition', don't fly like an idiot.

Sean-bumble-bee Posted at 12-14 13:31
How can anyone diagnose the problem with that drone when you are not even the pilot and there is no flight log?

That said a negative height of 400m is highly suspect unless the drone's firmware has been hacked to allow it to break 500m.

Someone whose hacked the firmware to break 500m should be also smart enough to disable auto landing from the parameters
I wonder if this problem is related to the barometer.

Kopanz Posted at 12-14 13:44
Someone whose hacked the firmware to break 500m should be also smart enough to disable auto landing from the parameters. I wonder if this problem is related to the barometer.

I wouldn't bet on their being smart enough to disable anything. Besides you can counter forced landing in its early stages at least via use of the joy sticks.
What is the point in wondering?
We will never know unless you can provide the flight log.

Dirty Bird Posted at 12-14 22:17
Watching this I am left scratching my head on what the pilot was thinking?  I don't know how the altitude wound up -485 meters but, if the drone mistakenly believes it is at -485 meters altitude, you know engaging RTH is going to force it to climb at minimum an additional 485 meters to 0 meters, plus your normal RTH altitude setting.  It's extremely windy.  WHY choose to engage RTH where it is going to add hundreds of meters in altitude & the wind will be that much stronger?  

Forget RTH.  JUST FLY THE BIRD HOME MANUALLY!   Use Sport Mode if necessary to overcome the wind.

This. 100% this.

Typical non experienced pilot, flying over see with lots of wind....

About this negative height (IMU error?)

a) if this value has been negative from the start of this flight...do not fly!
b) if values become negative in flight...uh,,,fly back home at once

Pilot initiate a RTH, with the amount of negative height,  drone will climb for ever to reach the RTH height setting. (battery drain for nothing...)( that is why a wrote "non expereienced pilot")
Only good action this situation : lower height to just above sea level, manual fly back home full forward stick and check distance decreasing. If not decreasing swith to sport mode and hope that a) it will win forom the wind and b) have enough juice to reach home.

But good video to make clear that flying drone is not that simple!

cheers
JJB

JJB* Posted at 2023-12-15 01:33
Typical non experienced pilot, flying over see with lots of wind....

About this negative height (IMU error?)

That is some good analytics from a fellow Dutchman.