Drone Manufacturer: DJI
Drone Model: Inspire 1 Pro
Country: United States of America
Pilot Qualifications: Licensed or Certificated by Aviation Authority Approved by Public Safety Agency or Company
Pilot Flight Experience: Unknown Hours
Link to External Information About This submission:
File Uploaded: None
I am a member of a Public Safety Agency in Eastern Washington State. I am the Team Leader and responsible person for our Unmanned Aerial System (UAS) component. On November 13, 2019 at 2130 hours we were conducting law enforcement training with our local K9 Units. We were training with permission in a salvage yard after hours. Deputy A was the Pilot in Command (PIC) and I was the Visual Observer (VO) for the UAS flight when the accident occurred.
The drone in question is a DJI Inspire 1 Pro. The Inspire was equipped with a single gimbal camera system and utilizing a Zenmuse XT thermal imaging (FLIR) camera.
Deputy A and I unpackaged the UAS from its hard case. We completed the checklist items for preparation for flight. It should be noted that I had just completed a Basic Drone Maintenance of the Inspire on November 12, 2019 and previous maintenance was also conducted in accordance with Airdata UAV’s maintenance schedule.
The flight was going as planned. Deputy A advised she had reached 30% battery life remaining which is the first of two warnings. These warnings are set at 30% for low battery warning and 15% for critical low battery warning. Deputy A advised the drone was about to reach or had just reached the Return to Home (RTH) setting when the power failure and accident occurred.
I was not watching the controller or the screen at the time of the accident. I was assigned as the Visual Observer (VO) and was watching the UAS and its position for potential flight hazards. I heard Deputy A state, “Aircraft Disconnected? My screen just went blank.” At about that time I saw the UAS fall out of the sky. I could not see the UAS strike the ground from my position. The UAS was in a hover at the time of the accident and it did not appear from my position to be moving.
Prior to the flight I looked at the airspace and time of day of the flights to be conducted. I found the area to be in Class D Airspace in a 300 foot UAS Facility Map area. Based on the training day and time of year I knew the training would occur at night time or darkness beyond civil twilight (Class E Airspace). Based on this scenario our agency has a Certificate of Authorization (COA) with the Federal Aviation Administration (FAA) allowing flight in controlled airspace at night as long as it is a public aircraft mission. Law enforcement training is considered a public aircraft mission. Since it is training and not an urgent mission I filed a Notice to Airmen (NOTAM) with 1800wxbrief.com for our training. The UAS can be flown without contact with the local Air Traffic Control (ATC) Approach prior to flying if a Notice to Airmen (NOTAM) has been filed.
A Risk Analysis was also completed prior to this flight. This flight, based on all information included in the risk form, was considered Low Risk.
As the responsible person, I noted before the training was to begin that Deputy A was out of currency for the UAS flight. By policy I had her conduct three take off and landings with a UAS prior to this flight in accordance with our policy. We were using a VO as required by our policy. Maintenance on the UAS and battery had been conducted in accordance with Airdata UAV’s maintenance schedule. Anti-collision white strobe lighting visible to three statute miles was being utilized at the time of accident as required by the FAA. Weather minimums were met as required by Part 107 licensing requirements.
Post-accident the UAS was located. I photographed the position of the UAS where it had landed. I observed no damage to any private property and nobody was injured on the ground. Once photographs were taken I collected the UAS, camera, gimbal and other UAS debris from the area. I placed the items on the floor and photographed them. I noted the battery life indicator lights on the battery began to blink showing one bar of battery life remaining. I videotaped the indicator lights flashing.
I next looked at the FLIR camera video at the time of the accident. The video does not show the UAS falling out of the sky, but instead the screen goes blank as if power was immediately stopped.
I synced the flight log from the Apple iPad mini DJI Go application into Airdata UAV for the UAS flights on the Inspire. I reviewed the flight and found the battery life for the I-2 battery was at 21% when the aircraft power loss occurred. I also looked at the voltage cells for the battery and noted that Cell 2 of 6 had major voltage deviations throughout the flight. I have never observed major voltage deviations prior to this date on any of my hundreds of flights or maintenance. I noted both other Inspire batteries used that night had voltage deviations as well. One battery had just two deviations throughout the entire flight and the other had deviations in one cell constantly throughout the entire flight like the accident involved battery.
The following day, I contacted the company the UAS was purchased from about the issue. It was determined we were out of warranty and that DJI only warranties batteries for six months. The company representative did state however that if the batteries sit for long periods of time without being used and/or not recharged regularly they can degrade over time. He recommended batteries be used generally for a year to a year and a half, but one may get more life if they are used regularly, for example monthly, and or charged regularly. He also added that we were not the first to call them regarding a battery going bad and an accident occurring.
I notified the FAA and the CAPS system regarding the incident as required by our COA by emailing them as well as completing the accident report on the CAPS system. Generally, UAS accidents are not reportable unless there is injury or damage to private property over $500, but COA requires a complete loss of aircraft to be reported. My opinion was that our aircraft was destroyed.
The battery system used for this flight was Battery I-2. This battery had never been serviced because it had not yet reached its basic service due dates based on the number of charges, flights or air time.
The information received from AirData shows a continuous voltage deviation throughout the entire 12-minute flight. I noted the voltage of the cell begins at 3.952v and continues above 3 volts until the last 4 seconds where it drops below 3 volts to as low as 2.907v. There were no on-screen warnings given to the Pilot in Command during flight of the voltage drops.
Sensor systems: Controller signal strength and GPS Signals were good during the flight:
I cannot say this accident was preventable. It is my conclusion that the power supply and battery failed mid-flight and there were no warning signs that Pilot in Command, Deputy A, could have foreseen that would have changed the outcome of this flight.
There are other checks that we will add to our maintenance schedule as well as checks pre-flight that may indicate an abnormal battery. It is unknown, in the short term, if these checks will diagnose, prior to flight, an abnormal battery system. We will continue to check the battery systems in Airdata UAV post-flight for any abnormalities and we can check the battery systems monthly and require batteries be used monthly. This may assist in prolonging battery life.
We can add checklist items to check voltage upon takeoff, but again it is unknown if the problem won’t present itself mid-flight. What we can do is continue to mitigate the unforeseen mechanical or power failure and do our best to not fly, especially hover, over people so when this happens again we avoid injuring those on the ground.
We may also consider replacement of battery systems yearly or on a time schedule determined to be beyond a normal batteries life. Another option is a drone parachute kit that may be fitted to a UAS system.
Here is a closer look and analysis of data from the flight.