What happened
On 20 April 2019, a DJI Matrice 210 was conducting a daylight survey operation in South Yorkshire near Dearne Old Moor. The flight was being performed under light wind conditions as part of emergency services operations. Following the completion of standard pre-flight inspections, the pilot ascended the small unmanned aircraft to an altitude of approximately 5 metres to conduct additional checks.
During the execution of small control inputs, the aircraft became unstable. This instability was accompanied by a structural failure in which one of the motor arms detached from the aircraft body. Consequently, the pilot lost control of the craft, resulting in a crash into the ground. There were no injuries reported as a result of the incident.
The investigation
Investigators examined the aircraft and analyzed the recorded flight data to determine the sequence of events leading to the loss of control. The examination focused on the mechanical integrity of the airframe and the performance of the propulsion system. The analysis of the onboard data logs revealed that the No 2 (front left) and No 3 (rear left) motors had experienced a stall. This loss of power resulted in a significant reduction of lift on the left side of the aircraft. However, the investigation could not definitively determine if the motor stalls occurred before or after the physical breakage of the motor arm.