What happened
On 13 December 2019, a DJI M600 Pro was being used for a commercial aerial survey of a construction site in Wallsend, Tyne and Wear. The flight was intended to be an automated mission, where the aircraft follows a pre-programmed route and lands without manual intervention.
During the final flight of the day, the aircraft reached an altitude of approximately 100 ft amsl when a GPS-compass error appeared on the controller. This error caused the aircraft to transition from automated flight into ATTI mode, a state where the drone can no longer maintain its position via GPS and is subject to drifting with the wind.
Instead of taking manual control, the pilot attempted to use the return-to-home function, which failed to respond due to the ongoing sensor error. Within ten seconds, the aircraft drifted behind a line of trees, resulting in a loss of visual line of sight. The drone continued to drift over an industrial area and toward a nearby housing estate. At 1521:07 hrs, the aircraft struck the roof of a house and fell into the rear garden. The impact caused damage to the propellers, arms, landing gear, gimbal, and camera lens. No injuries were reported.
The investigation
The AAIB investigation examined the aircraft's flight logs and the manufacturer's analysis of the error. The manufacturer determined that a mismatch between the GPS-derived heading and the magnetic compass heading, caused by signal interference, triggered the reversion to ATTI mode. This interference was also noted to have affected a secondary aircraft used during the search process.
The investigation also reviewed the pilot's training and the operator's procedures. While the pilot and observer held the necessary permissions for commercial operations, they had primarily relied on automated flight modes. The investigation noted that the pilots had not practiced emergency procedures or manual flight since completing their training in 2018.
Findings
- The transition to ATTI mode was caused by signal interference affecting the magnetic compass, creating a heading mismatch.
- The pilot and observer failed to apply manual control inputs to counteract the drift.
- The crew focused on attempting to use the automated return-to-home function rather than transitioning to manual flight.
- The loss of visual line of sight occurred quickly as the aircraft drifted with the wind.
- Manual flying skills are perishable, and the pilots had not practiced emergency maneuvers for over a year.
Safety action
Following the investigation, the AAIB issued Safety Recommendation 2020-017, suggesting that the UK CAA require PfCO holders to include routine emergency practice in their operations manuals to ensure pilots remain competent in manual flight.