During a search operation in the Oxfordshire countryside, a UK police drone lost connection with the controller and was found miles away in a children’s playground the next day, a report by the Air Accidents Investigation Branch (AAIB) has found.
According to the report, a $7,000 Parrot Anafi USA drone was being operated at night above a quarry to support search operations by Thames Valley Police. The pilot had completed preflight checks and checked the weather forecast before the flight.
However, as he gradually positioned the drone to hover over the quarry – approximately 120 meters away from the takeoff point – the pilot became aware of the presence of mist in the area. The blue LED visibility light on the aircraft also became harder to see, the pilot told the investigators.
As he was uncertain of the orientation of the drone, the pilot activated the Return to Home (RTH) function but the aircraft did not fly toward the takeoff point as he expected. He recalled that he pressed RTH once again to cancel the command, but the drone continued to fly in a northerly direction until it was out of sight and the screen of the controller went black.
The drone was found undamaged the next day in a playground more than three miles north of the takeoff point.
Need for better police drone training?
Though the UK’s Civil Aviation Authority (CAA) does not specify a minimum time for drone pilot currency, police forces in the country typically require qualified users to fly the aircraft for a minimum of two hours within a rolling 90-day period. If these requirements are not met, a flight assessment with the chief pilot or instructor becomes mandatory.
The AAIB report points out that, at the time of the accident, the drone operator had a total of 3.5 flight hours to his credit. Further, he had flown for only 90 minutes in the last 90 days before the Parrot Anafi USA drone was temporarily lost.
Following the accident that happened earlier this year, the pilot was instructed to undergo a period of retraining and reassessment, including:
- 5 hours one-to-one flight training with an instructor
- 1 month of coaching/shadowing with another competent drone pilot
- Flight assessment by an independent assessor from another police force
- A three-month review period
- Submission of a “human factors reflective practice report regarding omissions and learning”
Why did the RTH function not work on Parrot drone?
To understand what went wrong, the drone manufacturer analyzed the log file from the accident flight. Parrot found that the flight commenced 37 seconds after the drone was switched on, with the battery displaying 99% charge levels.
However, the drone did not acquire a GPS signal at any point prior to or during the flight. With the aircraft not being able to record the takeoff position, the RTH function was rendered ineffective.
The flight log further revealed that the RTH function was first selected after 3 minutes and 53 seconds of flight. It was then selected a further four times. The drone finally lost connection with the controller after 5 minutes and 53 seconds of flight, and was carried away by the wind.
Parrot stresses that its FreeFlight 6 app would have sent a “No GPS signal” alert to the pilot. Also, in the absence of GPS, the manufacturer expects its drone is either not flown or flown with extreme caution.
Nonetheless, the craft was still capable of responding to manual control inputs – even with the RTH function not working. However, no manual inputs were recorded after the initial attempt to activate the RTH function.
Now, the investigation report doesn’t say whether the presence of mist caused the pilot’s visual line of sight with the drone to be degraded or lost entirely. But visual contact with the drone was subsequently established as it drifted to the north. A more experienced pilot would have grabbed this opportunity to manually fly the aircraft back to the takeoff point.
And this is why the new period of re-training and re-assessment for the pilot proposed by the police force is substantially longer and more involved than that needed to achieve initial competence.
It’s also worth noting that Thames Valley Police has now amended its in-flight checklist to include an action to confirm the home point is locked, and if time permits, to check the RTH function. It also intends to fit additional LED lighting to its drones to assist in maintaining a visual line of sight at night.
The Parrot drone, meanwhile, is back in use.
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