A UK survey drone crashed into a house and fell outside due to GPS interference, according to a report by the UK Air Accidents Board. The 25-pound drone fell from a height sufficient to cause serious injury or death, but fortunately no one was present at the time.
A second drone sent to find the crash site suffered almost the same fate.
The incident happened in December during a routine site survey with a DJI Matrice 600 Pro, essentially a scaled-up version of DJI's consumer quadcopters. Operators had previously noted interference with the satellite navigation signal, but this had not caused serious problems. During the final launch, the drone climbed to an altitude of one hundred feet and reported a GPS compass error.
When this happens, the drone automatically returns to manual flight mode and hovers in place. It uses a barometric pressure sensor to maintain altitude, but without knowing its movement relative to the ground, it drifts with the wind. Normally the operator would take control, but in this case they were taken by surprise and the drone cruised behind the trees in a strong 15 mph wind, disappearing out of sight and out of manual control range at a site industrial.
The drone maintained its height above sea level, but rising ground meant it was level with rooftops when it reached a housing estate a few hundred meters beyond. It hit a house, damaging the rotors, and fell into the garden.
According to the UK DROPS standard for industrial safety, a blunt object weighing four pounds falling from six metres, the height of the fall in this case, can cause injury or death, even to a person wearing a helmet. The drone was six times heavier with a high risk of serious injury.
The drone operator launched a second drone to search for the crash site, as they only had a rough idea of where it was. It also gave a signal interference error and the second drone landed quickly and safely.
The source of the interference has not been identified. It may come from a GPS jammer. Sold as “personal privacy devices,” they can be easily obtained on the internet for $30. These are legal to own but illegal to operate in the UK They are typically used by lorry drivers and other people who do not want their vehicle's location recorded but interfere with all GPS receivers within sight. The GPS signal from orbiting satellites is very weak, equivalent to a car headlight 12,000 miles away, so it is easily overwhelmed by a nearby transmitter no stronger than a cell phone.
The incident raises questions about the safety of civilian drones, especially with larger drones that pose a significant risk of injury. Planned drone delivery services, like Google GOOGL+0.6%'s Wing and Amazon's Prime Air, will need robust navigation that won't derail - or crash - when exposed to GPS interference. Especially when there are a lot of people who don't like the idea of drones flying over their cities and are ready to take action against them. Accidental GPS interference is also a growing problem, with fears in the US that Ligado Networks' 5G transmitters will interfere with any precision GPS - like those in survey drones - within two miles.
The incident also highlights the need for military drones to have navigation methods other than GPS. Military-grade GPS jammer and spoofers, which give false location, are now being deployed as anti-drone defenses. Iran claims to have destroyed a US Sentinel RQ-170 with GPS spoofing in 2011; these devices are now increasingly available in the commercial sector, likely originating in China which appears to be using the technology to protect government facilities.
Although widely used by others, GPS is a military system, operated by the US Air Force. It is currently undergoing an upgrade, known as GPS Block III, which is estimated to cost over $5 billion but will not necessarily help prevent this type of incident.
“Low power means GPS is really, really, really easy to jam,” says Dana Goward, president and director of the Resilient Navigation and Timing Foundation. "GPS III offers jam-resistance improvements for military users with special equipment, but the 99% of civilian users will not experience any additional benefits at all."
Goward says making GPS truly robust and more resilient to local interference will involve building a much larger infrastructure and incorporating high-powered terrestrial transmitters as well as satellites.
“We need to start thinking about the overall architecture. What we need is a multi-layered architecture, with GPS and other satellites, something like eLoran for strong regional coverage, terrestrial, hard to disrupt, and wi-fi, cell towers, inertial systems and other approaches for local layers. Said Goward.
A one-time drone crash in the UK causing no casualties may not seem like a big deal. But some may see it as a sign of things to come.