What happened
On 17 July 2020, at approximately 02:45 UTC, a Parrot Anafi was being operated for emergency services purposes during a night-time search of rooftops in Yeadon, West Yorkshire. Roughly 15 minutes into the flight, while the unmanned aircraft system was at an altitude of approximately 50 feet above ground level, the pilot observed flickering on the control screen. Simultaneously, the motor speeds increased despite no pilot input. The aircraft began to turn and became unresponsive to manual controls. In an attempt to mitigate the situation, the pilot tried to descend for an emergency landing and activated the 'Return to Home' function, but the system failed to respond. The aircraft then entered an uncontrolled descent, striking a roof.
The impact resulted in minor damage to the roof covering, while the aircraft sustained damage to its battery and two propeller blades.
The investigation
The AAIB examined the wreckage and the pilot's report. The investigation noted that the pilot observed clean fractures on the propellers and observed the motors reacting in a specific manner. The investigation also referenced a previously reported propeller failure involving the same aircraft model in a prior AAIB bulletin.
Findings
- The pilot's observations of motor speed changes and propeller fractures suggested that the failure of two propellers was the primary cause of the loss of control.
Safety action
Following the incident, the operator updated its maintenance procedures. While the operator previously only replaced propellers that showed visible damage, they have now implemented a policy to replace propellers every 5 hours of flight time. Additionally, the operator will now record video of all pre-flight and post-flight safety inspections.