What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Unmanned aircraft (ua) privacy data omitted was launched at approximately 8:30 for an experimental r&d flight. The ua performed a vertical takeoff using all six motors and props, transitioned to forward flight for a short distance and had transitioned back to vertical flight for the descent and package delivery portion of the mission when it departed from controlled flight with a rapid roll to the right. A ground safety observer initiated flight termination system which commanded the ua to disconnect all power to all six of the motors. The ua fell approximately 120 feet and impacted the ground in an upside down position which minimized impact forces to the 18 pound lipo battery. The battery case was broken on forward bottom edge but did not have any resulting thermal runaway.
No pre-flight anomolies were detected.
Post-incident investigation revealed that the #2 propeller disbonded from the propeller hub causing a loss of torque and power. The flight control computer increased motor RPM to compensate for the lost torque and the motor shaft "wallowed out" the propeller mounting hole at the hub.
As the FAA filed it
UNMANNED AIRCRAFT (UA) ^PRIVACY DATA OMITTED^ WAS LAUNCHED AT APPROXIMATELY 8:30 FOR AN EXPERIMENTAL R&D FLIGHT. THE UA PERFORMED A VERTICAL TAKEOFF USING ALL SIX MOTORS AND PROPS, TRANSITIONED TO FORWARD FLIGHT FOR A SHORT DISTANCE AND HAD TRANSITIONED BACK TO VERTICAL FLIGHT FOR THE DESCENT AND PACKAGE DELIVERY PORTION OF THE MISSION WHEN IT DEPARTED FROM CONTROLLED FLIGHT WITH A RAPID ROLL TO THE RIGHT. A GROUND SAFETY OBSERVER INITIATED FLIGHT TERMINATION SYSTEM WHICH COMMANDED THE UA TO DISCONNECT ALL POWER TO ALL SIX OF THE MOTORS. THE UA FELL APPROXIMATELY 120 FEET AND IMPACTED THE GROUND IN AN UPSIDE DOWN POSITION WHICH MINIMIZED IMPACT FORCES TO THE 18 POUND LIPO BATTERY. THE BATTERY CASE WAS BROKEN ON FORWARD BOTTOM EDGE BUT DID NOT HAVE ANY RESULTING THERMAL RUNAWAY.
NO PRE-FLIGHT ANOMOLIES WERE DETECTED.
POST-INCIDENT INVESTIGATION REVEALED THAT THE #2 PROPELLER DISBONDED FROM THE PROPELLER HUB CAUSING A LOSS OF TORQUE AND POWER. THE FLIGHT CONTROL COMPUTER INCREASED MOTOR RPM TO COMPENSATE FOR THE LOST TORQUE AND THE MOTOR SHAFT "WALLOWED OUT" THE PROPELLER MOUNTING HOLE AT THE HUB.