Air taxi developers expect ADS-B tracking to have a big role in crowded skies
By Paul Brinkmann|March 6, 2023
Miniaturized tech makes matters less burdensome, though urban canyons present a challenge
Twenty years from now, hundreds of electric air taxis may fly the skies of major cities, threading needlelike corridors and altitudes where other aircraft, including tiny drones, may be forbidden to enter without authorization.
To plan for that, FAA and NASA continue to conduct research into new air traffic management methods. But one tool that FAA began requiring on all general and commercial passenger aircraft with electronics in 2020 is likely to remain: Automatic Dependent Surveillance-Broadcast Out, or ADS-B Out, an onboard transmitter that broadcasts the aircraft’s GPS location, altitude, ground speed, identity and other data once per second so they can be received by ground stations and other aircraft equipped with ADS-B In.
California-based Joby Aviation, which is the air taxi developer furthest along in terms of FAA type certification, conducts test flights with prototypes equipped with ADS-B, and intends for every aircraft it produces in the future to carry the technology, the company told me in an email.
But ADS-B might not function as well in skies crowded with advanced air mobility flights as it does today for higher-elevation flights, says William Semke, a professor of mechanical engineering and an associate dean at University of North Dakota’s College of Engineering and Mines
“In an urban canyon, between buildings, it might not transmit as well if you don’t have a line of sight. It doesn’t work great in an urban environment,” Semke says. “We’ll definitely have to set up flight paths, a highway in the sky or corridors if we really have thousands of air taxis over a city carrying people in them.”
Semke has studied the effectiveness of ADS-B in research partly funded by FAA. He says the susceptibility of ADS-B to jamming is a significant problem and could represent a vulnerability for air taxis.
An example of such jamming was documented in January 2022 when Israeli diplomats complained that Russian interference was blocking GPS data from flights entering Israel.
An ADS-B network can also “become oversaturated if you have too many flying vehicles all closely packed together, because there are just too many things on the screen to distinguish,” Semke says.
Regardless of its limitations, ADS-B is here to stay, Embry-Riddle Aeronautical University aerospace engineering professor Richard “Pat” Anderson told me. He is also the director of the university’s Eagle Flight Research Center.
“Even if we eventually have autonomous systems with no pilot on board, I would think there’s still going to be ADS-B on every aircraft, especially any carrying people,” Anderson says.
And while early ADS-B units were often too large for drones, some companies now produce tiny microchip ADS-B technology “no bigger than a postage stamp,” says Anderson, referencing as an example the products of Montana-based uAvionix.
As for problems with overcrowded skies and saturated signals, Anderson says software can be written so that pilots — on the ground or in the aircraft — only see the most crucial information, such as when a nearby aircraft has wandered outside its flight path or too close for comfort.
“Right now when I fly in the busiest airspace, I have my Garmin filter out things. If they’re not looking like they’re going to hit me, it doesn’t display those things,” says Anderson, a pilot.
But Anderson says he has two aircraft with no ADS-B because they have no electric systems — a glider and an aerobatic airplane in which the only electronics are in an engine starter.
Asked how he manages to avoid other aircraft, he says, “It’s the old-fashioned way: You got to look.”
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