The Aircraft Became Inverted At What Appeared To Be A Maximum Pitch Rate

Location: California City, California Accident Number: DCA23LA397
Date & Time: August 3, 2023, 08:03 Local Registration: N183TD
Aircraft: Supernal LLC SUP83-1 Aircraft Damage: Substantial
Defining Event: Loss of control in flight Injuries: 1 None
Flight Conducted Under: Part 91: General aviation - Flight test

Analysis: On August 3, 2023, at 0803 Pacific daylight time (PDT), a Supernal, LLC., SUP83-1 unmanned aircraft system, received substantial damage during a developmental test flight at the manufacturer’s test site. There were no injuries. The aircraft was operating with a FAA Certificate of Waiver or Authorization (COA) 2022-WSA-213-SAC-REV1, under Exemption No. 20050 Regulatory Docket No. FAA-2022-1757. According to the operator/manufacturer the accident occurred during the 3rd flight of the day. The test objective was to observe the behavior of the autonomous RTL (Return to Land) function, triggered by a “low” High Voltage (HV) battery warning.

Prior to the test, the voltage warning limits were adjusted in the ground control station (GCS) to trigger at a higher voltage than the previous flights. The previous test, i.e., the second flight of the day, had tested similar autonomous flight behavior using a hand-held transmitter (HHTX) lost link test point, and the aircraft turned towards home, and performed a “return to landing (RTL)” flight, as had been planned and expected.

On the third flight, at 7:59 AM local time the aircraft lifted off and the pilot translated the vehicle forward from the home position to the west corner of the landing pad and climbed the aircraft to 50 feet. Oscillations were noted, which the pilot said was because of wind, so he lowered aircraft to about 20-30 feet above ground level (AGL) to try and escape the turbulence. Upon reducing the aircraft’s altitude, the oscillations were reduced, but they were not completely gone.

With the extra battery power that remained before the low voltage alarm triggered, the pilot maneuvered the aircraft to the east and turned the left wing into the wind to see if it would further reduce the oscillations, but the maneuver had little effect. Then the pilot maneuvered the aircraft on the east side of the pilot’s station and placed it in a hover in front of the GoPro camera that was recording the flight, about 20 feet AGL, to await the reduction in battery voltage.

It took less than one minute for the low battery warning to trigger the RTL command, which the Ground Control Station Operator (GCSO) recognized and announced. At this point, the Flight Control Computer (FCC) took over control of the aircraft from the pilot’s HHTX and initiated autonomous flight. A few seconds later, the aircraft yawed left to point its nose towards the landing point with its tail pointing to the GoPro camera. Small oscillations were still noticeable, but the aircraft was in full control of itself, without any issues being noted.

After the aircraft turned left, there was a brief hover-hold before the expected aircraft translation was to occur, however at that point the aircraft became inverted at what appeared to be a maximum pitch rate. During the unexpected maneuver the wings stayed fairly level. As the nose pitched up, the aircraft translated backwards and looped over the top of the GoPro. As it was performing the loop it became inverted above the GoPro, and then continued the loop and rapidly descended until it landed directly behind the GoPro. When it landed it bounced and continued another “half-flip” and ended up laying on the ground, inverted.

Due to the low altitude and rapid loop/backflip maneuver, the duration of time from problem-initiation and recognition to actual ground-contact was too short for the pilot to react and attempt to recover control. After the aircraft impacted the ground, the pilot immediately activated the controls on the HHTX to disarm and deactivate the aircraft. During the maneuver, the aircraft’s trajectory was not close to any personnel, and no one was injured.

Upon impact with the ground the landing gear separated and the fuselage was fractured at multiple points. Most notably the canopy broke, and interior avionics tray dislodged, throwing the avionics battery clear of aircraft, through the opening created by the broken canopy. The right lift motor forward pylon also separated from the fuselage.

Postcrash examination and data review revealed that the accident was caused by the failure of a single lift-motor, which led to a loss of control. The motor failure was likely due to a soldering defect that led to the overheating and melting of a wire-solder joint, which led to a subsequent loss of electrical power to the motor.

The accident aircraft, a SUP83-1 unmanned aircraft system, serial number 001, manufactured in 2022, registered to TVPX Aircraft Solutions Inc., and operated by Supernal LLC., was a 25% subscale unmanned test aircraft used for the purpose of researching distributed electric propulsion technologies. The aircraft was configured with six propulsors driven by electric motors that are powered by lithium-ion battery packs. The aircraft can perform vertical take-offs and landings and can be reconfigured to horizontal flight with lift being generated by the wings. It is controlled from a handheld transmitter by a remote pilot and monitored by a PC laptop ground station linked to the aircraft via telemetry radios inside a mobile trailer at the test site. At the time of the accident the aircraft had accumulated about 2.6 hours of flight time on the airframe.

The pilot was an FAA certified private pilot who reported having 112 hours total flight experience and had no experience with the accident aircraft. The test flight was also supported by a visual observer who was stationed near the pilot and one team member who was located inside the ground control station. The pilot, visual observer, and ground control station operator used hands free headsets to maintain communication during the entire event, and they reported no communication issues among themselves.

The test site for this aircraft is a privately owned area near California City, California, within the Hyundai Motor Group’s California Proving Grounds automotive testing facility. Surrounded by unimproved desert, the test area has a large, paved ramp area from which operations are conducted along with the supporting infrastructure appropriate for the operations of the site. Per its COA, SUP 83-1 was permitted to fly within its test area up to 400 feet AGL, remaining clear of both Mojave Air and Space Port/Rutan Field’s (MHV) controlled airspace, and the Edwards Air Force Base (AFB) Restricted Area 2515.

Weather was not a factor in the accident. At the time of the accident, there were clear skies, the visibility was about 10 NM, the temperature was 24 degrees C, and the winds were variable at about 8 knots.

Probable Cause and Findings: The National Transportation Safety Board determines the probable cause(s) of this accident to be -- A loss of control in flight due to a loss of electrical power to one of the lift-motors.

FMI: www.ntsb.gov