Good spotting.
The "pilots" were out of their depth.
The incident report says that: No manual flight control inputs were made using the controller.
It would have been a very simple exercise to bring the drone back.
Despite the author's bio notes, it seems that he was going well beyond his actual level of expertise too.
David Hambling Author of 'Swarm Troopers: How small drones will conquer the world,' following cutting-edge military technology in general and unmanned systems in particular.
That's my take too. It seems there was some kind of EM/RF anomoly (it was a construction site they were surveying, which may have entailed a large amount of steel being around - that can absolutely interfere with the onboard compass). That caused the mismatch with GPS, so the aircraft switched to ATTI mode and started to drift. So far nothing unusual, and all within accepted behaviour patterns in that scenario.
Then it goes wrong. The pilot and spotter apparently did not even attempt to manually control the drone until it drifted out of VLOS. The report indicates that there was *no* disruption to comms between controller and aircraft, so it should have been perfectly possible for the pilots to bring the aircraft in for a manual landing. They also did not try and climb vertically once they lost VLOS, a fair obvious safety measure at that point given they had nothing else to lose.
Then it goes seriously wrong. Having suspected that the drone had crashed, they failed to consider possible causes of the first failure and *sent up a second drone* to look for it, which promptly experienced the same problems. This time they managed to bring it down safely in ATTI mode, which *really* makes me wonder why they didn't try that with the first one. They've both now been sent on a refresher training course, apparently.
Still, even if the interference was the result of deliberate (and illegal) jamming, I'd put this 100% down to pilot inexperience; issues like this can and do happen, and pilots, especially those with PfCOs (commercial licenses) should be aware of how to deal with them. I also know for a fact that at least some of the UK's pilot training schools include flying in ATTI mode as part of their tuition, so hopefully that is part of their new course.
IMO, if you are within VLOS then the *only* thing you need to bring an aircraft home safely is for it to respond appropriately to the sticks. Beyond VLOS, you can add the current bearing and (ideally) speed/distance to that - you should already *know* the minimum safe altitude you need to fly at. If you need RTH, to see what the drone's camera is looking at, or an arrow on a map, then that's just not good enough - especially if you are flying something like an Inpsire or a Matrice that could do some serious damage if it came down hard. And if you have a drone that lets you manually switch to ATTI mode, then you should regularly find a large open space on a breezy day and practice, practice, practice.