On October 17, 2019, at 1342 pacific daylight time (PDT), a Kitty Hawk Corporation Heaviside 2 unmanned aircraft system, N221HV, was substantially damaged during a manual precautionary landing in a field on the manufacture's test site. There were no injuries. The aircraft, which was performing an unmanned developmental test flight at the time of the accident, was operating as a Public Aircraft with an FAA Certificate of Waiver or Authorization (COA), under the oversight of the FAA Northern Plains Test Site. The aircraft was using developmental software, with a new version in development at the time of the accident.
According to the operator/manufacturer, approximately ten minutes into the test flight the aircraft encountered an anomaly while in conventional wing-borne flight at 2000 ft msl (approximately 700 ft agl). The ground station operator notified the Pilot-In-Command (PIC) that multiple flight computer limits were exceeded. The PIC took manual control of the aircraft and began descending the aircraft in preparation for an immediate landing. The PIC stated that he felt the aircraft had degraded control, and because the location on the test site was a large open field that allowed for a land out maneuver in any direction, he made the decision to perform a conventional landing into the wind. Once the aircraft approached the intended landing zone, the PIC slowed the aircraft by transitioning the aircraft towards a hover configuration until he felt there was additional risk to aircraft control if he transitioned further, and the aircraft landed with approximately 37 kts forward airspeed, 20 degrees nose down pitch, and 20 degrees left roll. The aircraft landed in a field of tall grass and suffered substantial damage.
The aircraft, which was not designed to land with forward velocity on unimproved surfaces, was substantially damaged during the landing. The canopy was separated from the fuselage and was laying on the ground on the right side of the aircraft. The nose section had also separated from the fuselage and was laying on the ground on the left of the aircraft pointing towards the empennage. The left canard was separated from the nose section near the canard root while the right canard remained attached to the nose section. The motors and propellers remained attached to their respective sections of the canard.
The fuselage demonstrated cracking on the lower left side just below and aft of the cockpit area. The landing gear and tail skeg were damaged and separated from the aircraft. The primary wing remained mostly intact; however, damage was noted to the left and right outboard motor fairings and the left outboard motor propeller was detached. There was no evidence of fire.
The accident aircraft was a Kitty Hawk Corporation Heaviside 2 unmanned aircraft system, serial number H2.2-003. The aircraft was in the developmental stage, and was intended to be an all electric single-seat aircraft that can operate like a conventional airplane in wing-borne flight with vertical takeoff and landing (VTOL) capabilities. It consists of a center fuselage, main wing, canard, and traditional airplane empennage with an elevator and rudder. The main wing contains ailerons and six (three on each side of the fuselage) VTOL electric motors with pusher type propellers. The canard also has two (one on each side of the fuselage) VTOL electric motors with pusher type propellers. The aircraft was being controlled and monitored from a ground station in a large tent structure on site, linked to the aircraft via a 2.4gHz radio connection.
The pilot was an FAA certified commercial airplane pilot, and reported 237 hours total time at the time of the accident. 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. There were no communication difficulties reported with the accident flight. The pilot, visual observer, and ground control station operator used hands free headsets to maintain communication during the entire event.
The Kitty Hawk test site is a privately owned ranch near Tres Pinos, CA. The ground is mostly natural with large areas of field and tall grass. Two paved 30x30 ft asphalt pads provide a surface for vertical take-off and landings. Per the COA, Kitty Hawk is authorized to fly in two areas (one 3 NM radius and one 5 NM radius) up to 5000 ft MSL at this test site location.
At 1340 PDT the weather at Hollister Municipal Airport (KCVH), approximately 12 miles from the test site, was reported as clear with winds from 330 degrees at 14kts gusting to 20kts.
A review of the recorded data by the operator/manufacturer revealed that a software timing error occurred which affected the controllability of the aircraft. The software timing error was caused by a battery charging script that, due to operator error, was not properly terminated at the ground station prior to the test flight. The improper termination resulted in the battery charging script running in an error state when it was not intended to be running, and the priority associated with the script allowed for the script to utilize significant processing resources. The manufacturer confirmed both the cause and effects of this timing error by recreating the sequence of events using a hardware in the loop simulator.
To address the anomaly encountered in this test flight, the manufacturer stated that they are making improvements to ground station and support equipment procedures. They further stated that future software versions will address processor priority issues to prevent similar timing errors from occurring. Finally, following the completion of these corrective actions, the manufacturer stated they intend to have their corrective actions validated by an external party review.