What aircraft was involved and where did it happen?

The accident on 2020-06-11 involved a Parrot Anafi Thermal, registration n/a, at Near The Dicker, East Sussex, GB.

What was the probable cause of the accident?

The loss of control was likely caused by the failure of the right front propeller during flight, leading to an unrecoverable descent and collision.

Unmanned Aircraft Collision with Tree in East Sussex

A Parrot Anafi Thermal drone experienced a loss of control during a commercial training flight, resulting in a collision with a tree near The Dicker.

What happened

On 11 June 2020, a Parrot Anafi Thermal was being operated for commercial training purposes near The Dicker, East and West Sussex. The flight involved a pilot and an observer conducting training maneuvers.

Approximately three minutes after takeoff, the unmanned aircraft began exhibiting unstable flight characteristics, described as "twitching." The pilot attempted to stabilize the craft, but it continued to pitch, yaw, and fluctuate in altitude by roughly 20 feet. In response to the instability, the pilot directed the aircraft toward an emergency landing area.

During the descent, the aircraft's responsiveness decreased significantly. The drone then pitched downward and moved away from the pilot without any manual input. Despite the pilot activating the 'return to home' function, the aircraft failed to respond to commands. The drone eventually struck a tree at an altitude of approximately 100 feet, roughly 420 feet from the intended landing zone. The impact caused damage to the gimbal and the right front propeller.

The investigation

The investigation was based on the accident report submitted by the pilot. Investigators examined the flight history and the mechanical state of the aircraft. The pilot noted that the flight behavior and the resulting damage suggested a failure of the right front propeller during flight.

At the time of the incident, the operator's maintenance protocol involved replacing propellers every 20 hours of flight time. The propellers involved in the accident had been in use for slightly less than 9 hours.

Findings

The aircraft experienced a loss of control characterized by erratic pitching, yawing, and altitude changes.
The drone became unresponsive to pilot inputs and failed to execute the automated return-to-home command.
The collision with the tree was preceded by a sudden downward pitch and uncontrolled movement.

Safety action

Following the incident, the operator updated its maintenance procedures. While propellers were previously replaced every 20 hours, the operator has now implemented a requirement to replace all folding propellers after 5 hours of flight time. This new interval has been integrated into the company's electronic flight and maintenance logging software.