I tried the steps explained by @AlexisTM, basically flashing APM and then PX4 Firmware. That solved several issues for me, namely
- Level Horizon “calibration failed: level”
- Detected 0 radio channels. To operate PX4, you need at least 5 channels
- PREFLIGHT FAIL MAG #0 SELFTEST FAILED
So what I did was, following the Intel Aero initial setup instructions:
cd /etc/aerofc/ardupilot/
sudo aerofc-update.sh arducopter-aerofc-v1.px4
Wait some minutes for the firmware to be flashed, and then:
cd /etc/aerofc/px4/
sudo aerofc-update.sh nuttx-aerofc-v1-default.px4
Note: I had to add sudo, otherwise it would not work. After this my drone, an Intel Aero RTF, worked correctly.