We had a regular flight to test new FPV antenna. Suddenly rear right motor cut out of the frame, tearing aluminium cross-piece and wires. We still don’t really know what happened, but most probable cause is propeller. It could be slightly damaged in transportation, or scrathched on landing. Imbalance caused propeller to crack in the air, and after propeller cracked, part of it was still attached to motor. Сentrifugal force did the last thing and teared motor off the aluminium frame. That is why it is always urgent to obey this rules:
1) Never pilot UAV above crowd, roads or houses! 2 killogram drone falling from 150 meters is a REAL disaster. People can be killed. It is third time I realize how it is important to obey this rule.
2) Examine propellers and whole drone before each takeoff and after each landing! Even slight imbalance will tear propeller to pieces at high RPM!