My friend asked me if I can ask somebody here for help analysing his crash. We really appreciate even little help.
It was his first flight with his new machine.
His pre flight and flight procedure was as follows:
1) He connected 3S battery.
According to Czech Republic laws drones has special restrictions for RTL.
One really important restriction is that RTL can not be used higher than 120 metres AGL.
When you fly drone above 120m and then you deploy RTL, drone should descent minimally