Unwanted minimum altitude in RTL mode


I was just testing some features of the RTL mode and had an unexpected behavior: when I brought my drone close to the groung (about 1m) and activate RTL mode, the drone is going up until about 2 m and then starts to get back to its home location. 

Problem is, I put RTL_ALT at zero and RTL_ALT_FINAL at zero too... 

My question: is there any "absolute minimal altitute" for the RTL mode ? If yes, is there any way to change it ? If no, does any one have any idea to explain this behavior ? 

For better understanding, you can see in the attached image (RTL_behavior.jpg) the drones behavior in altitude when I switch to RTL mode. As you might see, at higher altitude the drone doesn't change altitude when triggering the RTL mode, but once close to the ground (in the last minute) every time I switch to RTL the drone goes up a little.

(Also, in this flight record, the only moment I used the throttle to make the drone go up is at the beginning. Otherwise I only used it to bring the drone down so the upwards movements were done independently)

Any help is more than welcome. And ouf course, if you need more info i'll be happy to give it to you.

Thanks a lot for your help.


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  • Read the link and you'll understand the behavior.


  • Coming back with an update:

    I tried to do more or less the same using the auto mode. I configured a waypoint (LOITER_TIME 10 seconds) with an altitude of 0. This is supposed to bring the drone to the desired waypoint on the altitude the auto mode was switched.

    This works correctly. If I switch the mode at 10m height or at 1m height the behaviour is the same and the drone flies straight to the waypoint maintaining its altitude.

    So it looks like it's something related to the RLT mode...

    Any idea where it might come from ? 

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