Drone takeoff automatically & irregular descent

Hi :slight_smile:

I have 3 identical drone with pixhawk, at the factory settings and one of them, when I arm my engines in position mode, takes off alone. Is there a parameter for this?

And when the drone lands, it is difficult to detect the ground, so it takes off automatically after a few seconds …
I have to re calibrate the sensors and I can not find the right parameters …

Thanks.

Etienne