FA3HCWCR4X

HISTORY OF FLIGHT

On August 14, 2018, at 1330 eastern daylight time, at the Mountain Lake Biological Station, Blacksburg, Virginia, a Dà-Jiang Innovations (DJI) Phantom 4 small unmanned aircraft system (sUAS, commonly known as a drone), registration FA3HCWCR4X, operated by the Virginia Tech Conservation Management Institute (CMI), collided with a bystander resulting in minor injuries. There was no damage to the drone. The flight was an educational demonstration flight conducted in Class G airspace under the provisions of 14 Code of Federal Regulations (CFR) Part 107. Visual flight rules conditions prevailed at the time of the incident.

The flight was part of a demonstration for students of the Virginia Tech College of Natural Resources and Environment. There were six students observing the flight. According to the pilot, the demonstration was intended to consist of a short, automated flight over a pond using the DroneDeploy control application (app) to show how mapping surveys were conducted, followed by a manual flight to view wildlife in the pond. On the day of the incident, the pilot conducted a mapping flight prior to the demo. The pilot reported that, during the mapping flight, he attempted an automatic landing but the drone "missed its homepoint," and the Director of CMI hand-caught the drone. The pilot reported that he "used the manual shutdown procedure, which worked correctly."

The flight demonstration area was near a small beach and grassy area adjacent to the pond (figure 1). The area and the pond were surrounded by trees. Plastic lawn chairs and tables were in the area.

Figure 1 – Photo of Operating Area

The six students who were observing the demo flight were located less than 10 feet from the pilot. There was no visual observer or other assistant to the pilot for this flight. He started the demo in manual flight mode, and took off from a plastic picnic table on the berm of the pond. He reported the flight was normal, although the wind picked up a little bit during the flight. He flew the drone back to the picnic table for landing but reported that it would not touch down onto the table. The pilot reported that he made numerous attempts to land and attempted "the shutdown procedure," but the drone flew off to the side. He then reported that he climbed the drone back up and attempted an automatic landing and a landing in the grass, again using the "shutdown procedure," but the drone did not respond as he expected. He reported that he did not feel comfortable having one of the students try to hand-catch the drone, so he decided to crash it. The drone flew laterally and struck one of the students resulting in the injury, then continued into bushes where it stopped.

The pilot reported that the "shutdown procedure" that he used was to position the two control sticks (called a Combination Stick Command, or CSC) "down and in," meaning that the left (throttle/yaw) stick is pulled fully back and to the right, and the right (pitch/bank) stick is pulled fully back and to the left.

Examination of the logs revealed that, at 1 minute10 seconds before the end of data, the drone was being maneuvering at low altitude near the home point in GPS mode. Then the pilot partially decreased throttle followed by the "down and in" CSC.

Figure 2 – First CSC command 1:10 prior to end

According to the DJI Phantom 4 User Manual, the "down and in" command shuts down the motors immediately when the drone is on the ground. Alternatively, a method to stop motors on the ground is to retard the throttle straight back and hold for 3 seconds (figure 3). The method for emergency stop of motors in flight or prior to the drone sensing that it has landed is to pull the throttle back and to the right while simultaneously pressing the Return to Home button (figure 4).

Figure 3 – Excerpt from Phantom 4 User Manual, Stopping the Motors

Figure 4 - Excerpt from Phantom 4 User Manual, Stopping the Motors in Flight

The log data showed that, while the drone was still in the air, it responded to the pilot's "down and in" CSC input by pitching up, yawing right, and banking left. Logs indicated a "braking" message indicating the obstacle avoidance/visual positioning system (VPS) was activated.

The data showed that, when the pilot then neutralized the sticks, the drone hovered. Another braking message was recorded consistent with proximity to objects or persons. Fifty-four seconds prior to the end of data, the pilot activated the drone's "Autoland" feature, and the drone hovered briefly before the pilot input another "down and in" CSC. The drone again responded in pitch, yaw, and roll.

The data showed that, 49 seconds prior to the end of data, the pilot increased the throttle, and the drone climbed while still in Autoland mode. Ten seconds later, the pilot released the throttle, and the drone descended with no stick input, consistent with its Autoland feature. During the descent, another "down and in" CSC was given by the pilot, and again, the drone responded consistently. The logs indicated that, following each CSC, the drone's obstacle avoidance activated, consistent with the low altitude and proximity to objects and persons.

The drone subsequently climbed and then reentered an Autoland mode descent, and, at 28 seconds prior to end of data, the pilot reduced the throttle and held it fully back for less than a half second. The drone's automatic Landing Protection feature activated, consistent with the drone detecting an unacceptable surface to complete a landing while in Autoland mode. Twenty-two seconds before the data ended, the sequence repeated, with the pilot reducing the throttle, but not fully and only for 1.2 seconds. The DJI Phantom 4 User Manual describes numerous factors which will prevent the Autoland feature from completing the landing (figure 5).

Figure 5 - Excerpt from Phantom 4 User Manual, Landing Protection

The drone was maneuvered at low altitude until the pilot input a "down and in" CSC 4 seconds prior to the end of data; the drone responded in pitch, yaw, and bank, followed shortly by an ESC (electronic speed controller) error, which is consistent with the propellers striking objects. According to witnesses, the drone struck the ground and moved laterally toward the bystanders. The injured person attempted to jump out of the way, but the propellers struck her in the lower legs. The drone continued into nearby shrubbery, and the pilot retrieved it and shut down the power.

INJURIES TO PERSONS

First aid was conducted at the incident scene. The injured bystander received multiple lacerations to both legs requiring nine stitches, glue, and butterfly bandages at a hospital outpatient urgent care.

PERSONNEL INFORMATION The drone pilot held a Federal Aviation Administration (FAA) Part 107 Remote Pilot Certificate and had logged a total of 3.7 hours as Remote Pilot in Command (RPIC), most of which was on the senseFly eBee fixed-wing drone and the 3D Robotics (3DR) Solo quadcopter. He had logged 8 minutes RPIC on the Phantom 4 but reported about 2 hours of experience with it as a hobbyist. He was also experienced acting as Visual Observer and other crew positions. He did not hold any manned aircraft certificates.

His training on the Phantom 4 consisted of performing some basic maneuvers at a practice field using various DJI GO 4 functions, and practicing using the DroneDeploy flight control app. He reported experiencing no incidents during this training.

AIRCRAFT INFORMATION

The Phantom 4 is an sUAS of quad-copter configuration, about 13 inches in diameter. It is powered by four electric brushless motors and a 4-cell 15.2v lithium-polymer battery. The maximum takeoff weight is 3 pounds, maximum altitude is about 19,685 feet msl, and its maximum endurance is 28 minutes. Specified maximum range of the remote controller is 3.1 miles. The drone is equipped with a GPS/GLONASS navigation system and a flight controller enabling various automated functions. The drone is equipped with a 12-megapixel digital camera capable of still or video recording, and first-person view display. Aircraft telemetry and video is transmitted to the remote controller in the 2.4 gHz band and displayed on a smartphone or tablet of the pilot's choice using an app supplied by the manufacturer (DJI GO 4) or various third-party app developers.

The Phantom 4 includes a feature to provide automatic obstacle avoidance under certain conditions. Obstacle avoidance uses optical and ultrasound sensors to detect obstacles up to about 43 to 50 feet away from the drone and initiate braking or avoidance. The forward obstacle avoidance covers approximately a 60-degree field of view and downward covers approximately a 40-degree field of view. There is no obstacle avoidance in other directions.

The incident drone was being operated using firmware revision dated November 16, 2017. The pilot reported that he was controlling the aircraft via a Samsung Galaxy J7 smartphone using the DJI GO 4 app and that he normally conducted mapping flights using the DroneDeploy app. All obstacle avoidance and vision positioning systems were turned on.

The incident drone had been involved in a crash in May 2017, resulting in a tear to the shell and a misaligned motor. The drone was repaired in November 2017, and the compass and IMU (inertial measurement unit) recalibrated at that time. The compass and IMU had not been recalibrated since then.

METEOROLOGICAL INFORMATION

The weather station at the Biological Station reported temperature 80 degrees Fahrenheit, visibility 10 miles, wind at 8 knots. The weather observation at Blacksburg Airport, about 12 miles southeast of the accident site, reported wind from 240 degrees at 5 knots, 10 miles visibility, with scattered clouds at 4,100 feet above ground level.

AIDS TO NAVIGATION

Data logs from the drone indicated sufficient GPS signals throughout the flight. There were no NOTAMs of any GPS outages or anomalie...