What happened
On 15 October 2018, a DJI Matromice 210 was being operated as part of an emergency services mission to assist with vehicle crime prevention at the Merry Hill Shopping Centre in Brierley Hill. The flight was being conducted under drizzling conditions with light winds; however, the aircraft's IP432 rating meant the weather was considered suitable for the mission. To minimize risks to the public, the flight plan involved operating the unmanned aircraft primarily over buildings.
During the second flight of the day, the pilot brought the aircraft to a hover approximately 50 metres above a shopping centre roof. After roughly one minute of hovering, the aircraft experienced a sudden vertical descent, striking the building's roof. The impact resulted in the aircraft being destroyed. The pilot reported that no control inputs were made prior to the descent and no warnings had appeared on the controller.
The investigation
Investigators examined the recorded data from the aircraft to determine the cause of the sudden loss of altitude. The telemetry indicated that both batteries were operating normally, with a 65% charge and 22.8 V remaining at the moment of impact. Following a review of the flight data, the manufacturer identified that the loss of lift and subsequent loss of control were triggered by a failure in the electronic speed controller for the No 4 (right front) motor.