ADS-B and Part 107 Drone Operations
Several people who recently have taken their FAA Part 107 knowledge tests have told me that there were several questions about ADS-B (or at least answer choices that referenced ADS-B).
I found this kind of odd because ADS-B is a Part 91 regulation; and most drone operations the United States fall under Part 107, not Part 91. Enough recent test-takers have mentioned it, however, that I thought I should devote some attention to it.
The short version for those in a hurry is that the FAA does not require that Small Unmanned Aircraft Systems (drones that weight less than 55 pounds) be equipped with ADS-B. In fact, Section 107:53 expressly forbids the use of ADS-B Out in transmit mode.
What that means in terms of passing the Part 107 knowledge test is that any answer choice that suggests that transmitting over ADS-B Out is required or recommended by FAA for sUAS operations is the wrong answer. It is, in fact, prohibited unless you have special permission from FAA.
What is ADS-B, Anyway?
ADS-B stands for Automatic Dependent Surveillance-Broadcast. It's a system that used the aircraft's transponder to broadcast the aircraft's altitude, speed, location, and so forth so. It transmits once every second, and the broadcasts can be received by other aircraft and by ground stations.
ADS-B Out refers to the ability of the aircraft's transponder to broadcast, or transmit flight data. ADS-B In refers to the ability of a device to receive data broadcasted by other aircraft.
Some commercially-available drones are equipped with ADS-B In receivers, but none to date have true ADS-B transponders that can transmit. It would just clutter up the system with useless data. That's one of the reasons why ADS-B Out is not allowed to be used on sUAS in the United States.
The use of ADS-B In receivers to assist drone pilots in maintaining situational awareness, however, is not prohibited by Part 107. As of this page's most recent revision date, however, FAA has issued no official opinions recommending it, either.
If your drone is equipped with ADS-B In, I caution you not to trust it completely. There is no requirement that manned aircraft be equipped with ADS-B Out unless they're operating in airspace that requires it. Consequently, many smaller aircraft flying at low altitude don't have it, and those aircraft will not show up on your screen.
Why Not Use ADS-B Instead of RemoteID?
From the drone pilot's perspective, the reason is "because FAA sez so." In Part 107 operations, ADS-B is not a substitute for RemoteID and, once again, is explicitly prohibited. From the FAA's perspective, ADS-B was considered unsuitable for drones because it lacked functionality to associate the remotely-controlled sUAS with its operator on the ground.
In other words, in a manned aircraft, you know where the pilot is. He or she is in the aircraft. FAA wanted a way that the remote operator of a drone could be located, and ADS-B doesn't have that ability.
Revised November 17, 2022.