Drone Manufacturer: DJI
Drone Model: Matrice 210
Country: United States of America
Pilot Qualifications: Approved by Public Safety Agency or Company
Pilot Flight Experience: 1 Hours
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A flight demonstration was being done at our flight test facility. As part of the flight demonstration, we were showing a 3rd party loudspeaker attachment that had been procured for the Matrice 210.
There were no installation instructions for the loudspeaker kit. The speaker system consists of two speakers mounted on the opposing landing legs of the drone. The speakers are connected by a cable. The drone was being flown to different altitudes showing how the speakers would perform at different altitudes.
The drone was last demonstrated at an altitude of 350 feet. The demonstration was complete and 30 percent of the battery flight time was remaining. The drone was flown back to the Landing Zone.
However, the drone would not descend at a normal decent speed. The drone very slowly descended despite different attempts by various staff members to land the drone. Eventually, the batteries were exhausted and the drone was still 100 feet in the air. When the batteries died, the drone crashed to the ground.
The cause of the accident was that the cable passing between the two loudspeakers was not secured to the landing legs as far away as possible from the downward-facing sensors. As a result, as the drone was descending, it kept seeing the cable and thinking it was very close to the ground, and consequently, was descending at a very slow rate.
This information was determined by evaluating the flight data of the drone and seeing the reported altitude during the flight. Additionally, the flight crew was able to duplicate the behavior using another drone and similar conditions.