What happened
On 3 March 2019, a DJI Matrice 210 was being operated by the police for the purpose of an emergency services training exercise in Leicester. Before the flight, the pilot assessed the weather conditions; despite a forecast for rain, the pilot determined the flight could proceed because the aircraft possessed an IP432 environmental protection rating.
Following a successful take-off and the completion of necessary control checks, the pilot ascended the unmanned aircraft to an altitude of 90 m to ensure clearance from surrounding structures. While the aircraft was in flight, the rain transitioned from a steady fall to a light drizzle. Approximately five minutes into the mission, while the pilot was repositioning the drone, the aircraft began to spin uncontrollably. The pilot immediately attempted to alert bystanders to the danger. The aircraft fell to the ground over a period of roughly five seconds, resulting in the destruction of the aircraft upon impact. There were no injuries to any persons.
The investigation
Investigators analyzed the recorded flight data from the aircraft to determine the cause of the sudden loss of control. The examination of the onboard data revealed that a warning message regarding a motor blockage had been triggered during the flight. Further analysis established that the No 3 (rear left) motor had experienced a failure.