What happened
On 3 April 2021, a Parrot Anafi USA was being operated at night near Quarry Span Hill, Henley on Thames, to support police search efforts. The flight was conducted in low temperatures with light winds and mist. After the pilot positioned the drone approximately 120 m from the takeoff point, the mist made the aircraft's blue LED light difficult to track.
Concerned about losing visual line of sight, the pilot attempted to trigger the return-to-home (RTH) function. However, the aircraft did not return to the launch site. The pilot attempted to cancel the command, but the drone continued flying north until the connection to the controller was lost. The aircraft eventually performed an automatic landing and was located the following day, undamaged, roughly 5 km away.
The investigation
Data from the manufacturer's log files revealed that the drone had failed to acquire a GPS signal at any point during the flight. Because no GPS signal was established, the aircraft had not recorded its takeoff coordinates, which made the RHD function non-functional. The manufacturer noted that the control application would have provided alerts regarding the lack of GPS signal, suggesting the aircraft should not have been flown, or should have been operated with extreme caution.
Investigators also reviewed the pilot's experience and the operator's procedures. At the time of the incident, the pilot had approximately 3.5 total flight hours. While the pilot had recently undergone training to re-establish currency, the investigation noted that the operator's internal requirements for re-assessment following a period of inactivity may not have been clearly monitored.
Findings
- The RTH function failed to return the aircraft to the takeoff point because the drone had not acquired a GPS signal prior to or during the flight.
- The lack of a recorded home point rendered the automated return command ineffective.
- Mist in the area had degraded the pilot's ability to maintain visual contact with the aircraft's lights.
- The pilot's recent flight experience was limited, with only 1.5 hours on this specific model.
Safety action
Following the incident, the operator updated its In-Flight Checklist to include a specific step to confirm the home point is locked and to verify the RTH function is operational. Additionally, the operator plans to install extra LED lighting on its drones to improve visibility during night operations.