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Drone Crash Due to Battery Failure

Thursday, September 20, 2018 14:30

Imagine flying your unmanned aerial vehicle (UAV, a.k.a. drone) 200' above the ground and the blades suddenly stop spinning and your 10 pound UAV hurtles to the ground as dead weight?

It does happen and here is the story of our experience along with learnings. We were flying our DJI Inspire 2 aircraft recently and brought the aircraft in for a safe landing when we reached the 25% battery level. Shortly after landing, we took off again via the launch button in the DJI Go 4 app to check a reading. The aircraft rose and hovered at the standard ~6' hover height to allow for testing of controls per standard operating procedure (SOP). As part of the SOP, we checked the battery levels. One battery read 17% capacity remaining and the other read 15% capacity. This in of itself is an anomaly as both batteries should read the same level.  At that point, we pressed the land icon on the app.  By the time the message opened in the app asking to confirm landing, the motors stopped spinning and the aircraft crashed to the ground. The camera and gimbal were severely damaged since the landing gear had not lowered.

Upon returning to the office, we put all 4 pairs of batteries that we had with us on the DJI battery charging station. The status for the one battery that read 15% showed "permanent failure." We called DJI to discuss what may have gone awry. They directed us to send the aircraft, controller, camera, and batteries in for analysis and repair. Turns out the battery failed causing a loss of power and hence the crash and camera damage. As to why the battery failed, they did not provide a clear cut answer.  They did say though that battery storage may have been a cause - either storing it for a "long time" or in temperatures outside of the manufacturer's recommendation. It had been about a month since this battery pair was last flown.

Learnings. 

  • Though the DJI Inspire 2 has redundant compasses, barometers, and electronics, the two batteries are NOT in a redundant configuration. Tech support says that if one of the two batteries fail in flight, then the aircraft immediately loses complete power.  
  • DJI announced several months ago that these Inspire 2 TB50 batteries are reporting voltage imbalances between their internal cells.  DJI acknowledged that it is a firmware issue.
  • It is important to follow DJI's battery maintenance and storage guidelines, which among other things, include discharging the batteries to 40% - 65% if NOT intended to be used for more than 10 days, and to fully charge and discharge the batteries at least once every 3 months. We now emphasize this in our SOPs.
  • We will look into add-on parachute systems as a contingency for unplanned power failures in mid-flight.
  • Commercial Inspire 2 owners that are primarily real estate agents, inspectors, or surveyors for example and who do not fly their aircraft frequently as a result, may want to assess whether it makes sense to add frequent flying or battery maintenance procedures to their business operations or to contract out aerial photography and video to service providers that have the processes and disciplines in place to assure airworthiness readiness for their aircraft.
  • We are thankful for having this experience at only 6' above the ground and not 100', 200', or higher.