What happened
On 17 August 2021, a DJI Matrice 300 was conducting a private aerial search flight at night near Cam, Dursley, in Gloucestershire. The mission had been underway for approximately 18 minutes and was proceeding without any reported malfunctions. As the unmanned aircraft was approaching its primary landing site at an altitude of roughly 30 m, it suddenly became unresponsive to control inputs and fell directly to the ground. The impact resulted in significant damage, specifically causing the motor carrier arms to break away from the main casing.
The investigation
Investigators examined the wreckage to determine the cause of the sudden loss of control. The aircraft features a design where the motor arms are hinged to allow for folding during transport, secured by a 'twist to lock' collar mechanism. Upon inspection, the operator noted that three of the four arms had detached from the structural casing, but their locking collars remained intact and undamaged. However, the fourth arm showed a different pattern of failure; the hinge had broken, and the associated locking collar was found loose and displaced along the arm.
Findings
- The investigation identified that the fourth motor arm's locking collar was not properly secured.
- The physical evidence suggests that the locking collar may not have been fully engaged, potentially allowing it to loosen during flight.
- A loose arm could lead to variable thrust from that specific rotor, which would render the aircraft unable to maintain stability or respond to pilot commands.