There’s been a lot of talk over the years about endowing drones with the ability to “sense and avoid” nearby aircraft—adding radar or optical sensors that would mimic what a pilot does when she peers out the window in all directions to be sure there are no other aircraft nearby on a collision course. But incorporating such sense-and-avoid capability is quite challenging technically, and would probably never be possible to add to small consumer drones.
Thankfully, the threat of mid-air collision can be reduced using a strategy that is much easier to implement: Have aircraft track their positions with GPS and then broadcast that information to one another, so that everybody knows where everybody else is flying. Drones could at least receive those broadcasts and alert their operators or automatically adjust their flying to steer well clear of planes and helicopters.
Indeed, DJI, the world’s leading drone manufacturer, has already outfitted some if its drones with just this ability, and today it announced that by 2020 it would include that feature, which it calls “AirSense,” in all new drones it releases that weigh more than 250 grams.
What’s behind AirSense is something called ADS-B. So let me take a moment to briefly explain what that is.
The acronym itself stands for Automatic Dependent Surveillance-Broadcast. There are really two flavors of this equipment: ADS-B in and ADS-B out. An aircraft equipped with ADS-B out will periodically send out information about its position, altitude, velocity, and so forth. These transmissions occur (A)utomatically; the information reported is (D)ependent on satellite-navigation equipment on board; and it is transmitted to no one in particular, meaning it’s (B)roadcast. Hence the clunky four-letter acronym.
Aircraft equipped with ADS-B in, as well as air-traffic controllers, merely receive the ADS-B out signals. This system of broadcasting where you are and where you are headed allows aircraft equipped with ADS-B out to be tracked without the need for radar. Some countries already require it. For example, Canada uses ADS-B to control air traffic around Hudson Bay, where radar coverage is spotty.
In 2017, DJI introduced its Matrice 200 series drones, which included ADS-B in as part of the drone’s AirSense system. And last October, DJI unveiled a drone it calls the Mavic-2 Enterprise, which it similarly equipped with ADS-B in and AirSense. The ADS-B receiver is placed in the drone itself, which being airborne has good reception of radio signals from nearby aircraft. DJI’s AirSense system relays this information to the drone’s ground controller, which sounds an audible and vibratory alarm, alerting the operator that there is an aircraft flying nearby.
AirSense doesn’t force the drone to land, though, nor does it carry out any other kind of evasive maneuver automatically. “We could program that,” says Brendan Schulman, vice president for policy and legal affairs at DJI. “But we felt that the operator was in the best situation to make that judgement.”
So someone flying these types of high-end DJI drones are right now able to know where nearby aircraft equipped with ADS-B out are located, and they have been using that to good effect, says Schulman. Today’s announcement from DJI is that, by January 2020, pretty much all of the company’s new drones will have this feature.
The timing of this rollout isn’t accidental. By January 2020, most aircraft in the United States must be equipped with ADS-B out. (There are exceptions, such as for gliders and balloons, or for aircraft operating only in uncontrolled airspace.) This is needed for the next generation of air-traffic control, which will rely principally on these ADS-B signals, rather than radar. “We’ve aligned our schedule with that,” says Schulman.
Adding this capability to drones makes good sense: it’s relatively easy to do and can only enhance safety to have drone operators be able to know where nearby planes and helicopters are operating, even if they are too far away to easily perceive with eyes and ears.
Why then not have drones carry ADS-B out as well? Then pilots would be able to see on their cockpit display where nearby drones are flying.
Schulman explains that “the FAA [U.S. Federal Aviation Administration] has told us this would be undesirable.” That’s because there are so many drones around these days that equipping them with ADS-B out would in many places overwhelm the system the FAA has for tracking these signals. Even without that worry, it would distract pilots unnecessarily, given how low most drones fly.
DJI is willing to entertain the notion of one day putting ADS-B out into its drones. But the company won’t pursue that strategy, says Schulman, “until there is better [regulatory] guidance about how to do that.”
David Schneider is a Senior Editor at IEEE Spectrum. He worked for Scientific American and American Scientist before joining the Spectrum staff. In a former life he did research in geophysics. His beat focuses on computing, although he often blogs about drones and frequently writes for Spectrum's Hands On column, which betrays his MacGyverish tendencies. Schneider has, for example, build a synthetic-aperture radar using coffee cans and was able to detect an extrasolar planet using mostly stuff you can buy at the mall. He holds a bachelor's degree in geology from Yale, a master's in engineering from UC Berkeley, and a doctorate in geology from Columbia.