What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
N579PA, an privacy data omitted MK27, s/n 355, was operating from PDT airport on 06/21/2021 under a special experimental airworthiness certificate for r&d purposes when it experienced a loss of power to the number one motor. This occurred just after completing the outbound leg of a maintenance check flight from the privacy data omitted launch area near their hangar at the PDT airport. After the UAS took off from the drop off location about 1/2 mile nw from the PDT airport, it climbed vertically to about 180 feet and began a transition from vtol mode to forward horizontal cruise flight mode for the return leg to the PDT base. The safety officer (so) onsite at the drop off location reported seeing the UAS climb without incident to 180 feet, but when the UAS began its attitude rotation for forward flight, the so reported seeing the aircraft rotate to the right and then drop vertically 10 to 20 feet in a fully inverted position. The ground station operator (gso) and the PIC (oic) monitoring this flight reported seeing a propulsion warning light in the ground control station, and at the same time, the UAS automatic onboard health monitoring system detected a failure in the #1 electronic speed control (esc) and initiated an immediate "urgent land" command. The so stated that as soon as he saw the UAS flip inverted he hit the flight termination system (fts) emergency stop button. This button causes all escs to go to zero RPM and flight servos to go to a pre-commanded position to limit glide of the UAS. The so stated the UAS fell vertically from about 160 feet in a straight down trajectory.
Review of video taken by the so of this event showed the UAS tumbling in uncontrolled free fall until it contacted the ground about 400 feet from the so?s position. After impact, sections of the flight controls and structure broke off, and the so reported seeing smoke and then flames within about 5 seconds. The so asked the oic to call the fire department to report the fire that had broken out in a wheat stubble field, as an intense lithium battery fire quickly consumed the aircraft. Several acres of wheat stubble field were soon on fire, which the fire department extinguished after arriving about 5-10 minutes after getting the emergency call. On-site inspection of the UAS remains by iic via privacy data omitted later that day found nothing recognizable left of the aircraft after the fire except for the burned remains and melted metal components.
privacy data omitted Representatives reported that this serial number UAS had experienced controller area network (can) issues just before this flight, and that the number one motor had stopped during launch two days before this event. They reported the number one esc and number one motor had been changed just before the flight on June 21, and that the purpose of this flight was a post maintenance check after successful tether flight tests.
As the FAA filed it
N579PA, AN ^PRIVACY DATA OMITTED^ MK27, S/N 355, WAS OPERATING FROM PDT AIRPORT ON 06/21/2021 UNDER A SPECIAL EXPERIMENTAL AIRWORTHINESS CERTIFICATE FOR R&D PURPOSES WHEN IT EXPERIENCED A LOSS OF POWER TO THE NUMBER ONE MOTOR. THIS OCCURRED JUST AFTER COMPLETING THE OUTBOUND LEG OF A MAINTENANCE CHECK FLIGHT FROM THE ^PRIVACY DATA OMITTED^ LAUNCH AREA NEAR THEIR HANGAR AT THE PDT AIRPORT. AFTER THE UAS TOOK OFF FROM THE DROP OFF LOCATION ABOUT 1/2 MILE NW FROM THE PDT AIRPORT, IT CLIMBED VERTICALLY TO ABOUT 180 FEET AND BEGAN A TRANSITION FROM VTOL MODE TO FORWARD HORIZONTAL CRUISE FLIGHT MODE FOR THE RETURN LEG TO THE PDT BASE. THE SAFETY OFFICER (SO) ONSITE AT THE DROP OFF LOCATION REPORTED SEEING THE UAS CLIMB WITHOUT INCIDENT TO 180 FEET, BUT WHEN THE UAS BEGAN ITS ATTITUDE ROTATION FOR FORWARD FLIGHT, THE SO REPORTED SEEING THE AIRCRAFT ROTATE TO THE RIGHT AND THEN DROP VERTICALLY 10 TO 20 FEET IN A FULLY INVERTED POSITION. THE GROUND STATION OPERATOR (GSO) AND THE PIC (OIC) MONITORING THIS FLIGHT REPORTED SEEING A PROPULSION WARNING LIGHT IN THE GROUND CONTROL STATION, AND AT THE SAME TIME, THE UAS AUTOMATIC ONBOARD HEALTH MONITORING SYSTEM DETECTED A FAILURE IN THE #1 ELECTRONIC SPEED CONTROL (ESC) AND INITIATED AN IMMEDIATE "URGENT LAND" COMMAND. THE SO STATED THAT AS SOON AS HE SAW THE UAS FLIP INVERTED HE HIT THE FLIGHT TERMINATION SYSTEM (FTS) EMERGENCY STOP BUTTON. THIS BUTTON CAUSES ALL ESCS TO GO TO ZERO RPM AND FLIGHT SERVOS TO GO TO A PRE-COMMANDED POSITION TO LIMIT GLIDE OF THE UAS. THE SO STATED THE UAS FELL VERTICALLY FROM ABOUT 160 FEET IN A STRAIGHT DOWN TRAJECTORY.
REVIEW OF VIDEO TAKEN BY THE SO OF THIS EVENT SHOWED THE UAS TUMBLING IN UNCONTROLLED FREE FALL UNTIL IT CONTACTED THE GROUND ABOUT 400 FEET FROM THE SO?S POSITION. AFTER IMPACT, SECTIONS OF THE FLIGHT CONTROLS AND STRUCTURE BROKE OFF, AND THE SO REPORTED SEEING SMOKE AND THEN FLAMES WITHIN ABOUT 5 SECONDS. THE SO ASKED THE OIC TO CALL THE FIRE DEPARTMENT TO REPORT THE FIRE THAT HAD BROKEN OUT IN A WHEAT STUBBLE FIELD, AS AN INTENSE LITHIUM BATTERY FIRE QUICKLY CONSUMED THE AIRCRAFT. SEVERAL ACRES OF WHEAT STUBBLE FIELD WERE SOON ON FIRE, WHICH THE FIRE DEPARTMENT EXTINGUISHED AFTER ARRIVING ABOUT 5-10 MINUTES AFTER GETTING THE EMERGENCY CALL. ON-SITE INSPECTION OF THE UAS REMAINS BY IIC VIA ^PRIVACY DATA OMITTED^ LATER THAT DAY FOUND NOTHING RECOGNIZABLE LEFT OF THE AIRCRAFT AFTER THE FIRE EXCEPT FOR THE BURNED REMAINS AND MELTED METAL COMPONENTS.
^PRIVACY DATA OMITTED^ REPRESENTATIVES REPORTED THAT THIS SERIAL NUMBER UAS HAD EXPERIENCED CONTROLLER AREA NETWORK (CAN) ISSUES JUST BEFORE THIS FLIGHT, AND THAT THE NUMBER ONE MOTOR HAD STOPPED DURING LAUNCH TWO DAYS BEFORE THIS EVENT. THEY REPORTED THE NUMBER ONE ESC AND NUMBER ONE MOTOR HAD BEEN CHANGED JUST BEFORE THE FLIGHT ON JUNE 21, AND THAT THE PURPOSE OF THIS FLIGHT WAS A POST MAINTENANCE CHECK AFTER SUCCESSFUL TETHER FLIGHT TESTS.