PX4 PRO is a software middleware for autonomous systems and robots used to build a wide variety of drones. According to its official documentation:
PX4 can fly anything from a racing to a cargo drone - be it a multi copter, plane or VTOL.
Connect your Erle-Brain 3 to internet, open one terminal and execute the following commands:
NOTE: You need update the key of your image (after 20-09-2017).
curl packages.erlerobotics.com/keys/deploy | sudo bash
sudo apt-get install px4-erle-robotics
Open a terminal and type the following:
sudo apt-get purge -y px4-erle-robotics
PX4 official link.