What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
privacy data omitted Was launched from the test area as a post-maintenance check flight after the replacement of the #6 propeller to newest design/part number. Immediately after start of all six motors the unmanned aircraft sharply rolled to the left and hit the ground up-side-down position. Power to all six motors was turned off using flight termination system.
Post-incident investigation revealed that the newly installed #6 propeller was actually a #1 propeller (marked with the wrong part number). The installed propeller was designed for counter-clockwise rotation but was installed on a clockwise rotating motor. Resultant lift and thrust would be opposite of intended as motor RPM increased. Proper control by the unmanned aircraft flight control computer would be impossible in this configuration.
As the FAA filed it
^PRIVACY DATA OMITTED^ WAS LAUNCHED FROM THE TEST AREA AS A POST-MAINTENANCE CHECK FLIGHT AFTER THE REPLACEMENT OF THE #6 PROPELLER TO NEWEST DESIGN/PART NUMBER. IMMEDIATELY AFTER START OF ALL SIX MOTORS THE UNMANNED AIRCRAFT SHARPLY ROLLED TO THE LEFT AND HIT THE GROUND UP-SIDE-DOWN POSITION. POWER TO ALL SIX MOTORS WAS TURNED OFF USING FLIGHT TERMINATION SYSTEM.
POST-INCIDENT INVESTIGATION REVEALED THAT THE NEWLY INSTALLED #6 PROPELLER WAS ACTUALLY A #1 PROPELLER (MARKED WITH THE WRONG PART NUMBER). THE INSTALLED PROPELLER WAS DESIGNED FOR COUNTER-CLOCKWISE ROTATION BUT WAS INSTALLED ON A CLOCKWISE ROTATING MOTOR. RESULTANT LIFT AND THRUST WOULD BE OPPOSITE OF INTENDED AS MOTOR RPM INCREASED. PROPER CONTROL BY THE UNMANNED AIRCRAFT FLIGHT CONTROL COMPUTER WOULD BE IMPOSSIBLE IN THIS CONFIGURATION.