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Pro Tips for Private Pilots: ADS-B, Are You ‘In’ or ‘Out’?

A review of the surveillance technology landscape.

Four years after the ADS-B mandate, the options for both ADS-B In and Out are plentiful. [image: Adobe Stock]

January 1, 2020, was a red-letter day in the transition to automatic dependent surveillance-broadcast (ADS-B). ADS-B Out was required in Class A, B (including the Mode C veil), and C airspace in the United States, as well as generally above 10,000 feet.

However, unless general aviation pilots decided to go a step further and equip their aircraft for ADS-B In, their flight deck situational awareness was little improved.
My epiphany on this subject of ADS-B occurred a couple of years earlier. I had flown our university fleet equipped with ADS-B In since 2003, but my pocketbook dictated the lower-cost Out option for our personal ride. Then, my attitude changed. Climbing east out of Montgomery-Gibbs Executive Airport (KMYF) in downtown San Diego, I switched from tower frequency to approach control and immediately heard the collision alarm ringing in the background.

Bringing my eyes smartly up from the BendixKing KX-155 radio face, I was greeted by the sight of a Cessna twin in my windshield. We were offset slightly, and each banked hard away from the other, but the passage was close enough to read the N-number without much difficulty.

For those unfamiliar with this particular patch of airspace, traffic heading both east and west encounters a shallow band of uncontrolled airspace between the top of the Gillespie Field (KSEE) 2,400-foot Class D airspace, located a few miles west of Montgomery-Gibbs, and the 4,800-foot floor of the San Diego Class B. Nearly all traffic in this little piece of sky is either climbing or descending, so cardinal altitudes are not much help. I had a long time to think about that close call on the two-hour flight back to Prescott, Arizona, and decided right then and there that we would find the extra bucks to go for the whole enchilada, ADS-B In. I have not regretted that decision.


ADS-B In, Out, or Both?

When I decided to break the piggy bank and install ADS-B In, the cost was fairly significant. And with an FAA mandate approaching, discounts were hard to come by. Today, the opportunities for ADS-B In and Out installations are much more affordable. Additionally, portable ADS-B In solutions are available that data link to your iPad. However, not all ADS-B systems are created equally.

Above 18,000 feet, and generally around the world at all altitudes, 1090 MHz ES (extended squitter) rules the roost. However, in the U.S., below Class A airspace, 978 MHz UAT (universal access transceiver) is preferred. Most transponders have both, but some portables may, or may not. UAT allows the ADS-B In user to obtain flight information services (FIS-B) for weather and useful flight information, and traffic information services (TIS-B). TIS-B provides non-ADS-B radar target information from local ATC radars through the ADS-B ground stations.

The moral of this story is that it is up to each pilot to fully understand what information and protections their particular ADS-B In system provides.

‘O Canada’

Once across our northern border, the FIS-B and TIS-B services provided by the U.S. 978 MHz UAT are no longer available. And while the FAA remains committed to its ground-based system, Nav Canada is rapidly converting to satellite-based ADS-B. Pilots flying in Canadian Class A airspace after August 10, 2023, are required to have antenna diversity. This is a fancy term for an additional antenna on top of the airplane.


The satellite-based ADS-B mandate extends to Class B airspace in May 2024, and likely to the rest of Class C, D, and E airspace in the 2026 to 2028 time frame. Some lower-cost ADS-B Out solutions already meet that requirement, especially those mounted on wing and tail beacon sockets. However, many legacy ADS-B In solutions will require an additional antenna, and some systems may not support antenna diversity at all. All good things to know if you are flying north to enjoy the amazing Canadian hospitality.


For the record, in the VFR environment, the “Mark One Eyeball” mode is still king. However, in this see-and-avoid environment, ADS-B really shines. GA aircraft are pretty hard to see more than a couple miles away. If the lighting and contrast are just right, our little planes might be visible from 4 to 5 miles away, but that is the exception to the rule.

Once the sun sets, visibility is much better, especially on clear nights with landing, strobe, and position lights on. However, at night long-range depth perception can be a problem. A 10-mile distant target can appear close, and vice versa. Day or night, ADS-B In makes it easier to correlate the range to the target and find the perfect quiet spot in the practice area, 15 miles ahead. However, ADS-B In is only a tool, and a thorough visual scan is critical. Outside of controlled airspace, some aircraft have ADS-B In, some ADS-B Out, and some have nothing at all. So, relying on the ADS-B traffic display to separate us 100 percent of the time is unwise.

ADS-B is also very useful when approaching a nontowered or Class D airport. Ten miles out, ADS-B In is a great planning tool to identify who is in the pattern, who is approaching the airport, and where we might sequence in. Once we get closer, the transition to visual separation and reliance on the aural warnings provided by the ADS-B In system become the better option.



ADS-B presents your aircraft differently on the radar controller’s scope. Traditionally, radar targets update every six seconds for approach control and every 12 seconds for an en route display. ADS-B targets update every second, so controllers see them move smoothly across the screen. In the en route environment, this allows radar controllers to reduce separation from 5 nm to 3 nm. On the other hand, with ADS-B In targets fed into our flight deck display, it can be mighty tempting to “help out” the air traffic controller.

Resist this temptation to assist by quietly changing speed or direction. Self-separation is not allowed in the IFR environment. However, if a pilot sees that they are losing separation with other traffic, or that a change in their clearance might help smooth out the traffic flow, the controller will welcome the call, issue updated instructions, or explain why not.

All Towers Are Not Equal

Federal ATC towers are most often equipped with the same ADS-B, and primary and secondary radar found in the approach control. However, some FAA contract towers are not, so following their instructions to the letter, keeping your eyes out the window, and monitoring the ADS-B In display is a great backup to ensure safe separation.

“What we’ve got here is a failure to communicate.”—Cool Hand Luke

Gone are the days of “Tally Ho,” climb to “Angels 15,” and, even more recently, “Taxi into position and hold.” These “Battle of Britain” holdovers sound great but did not make it into the pilot/controller glossary. However, when we hear pilots identify traffic on ADS-B, it often sounds like, “got it on the fish finder,” “gadget,” or “gizmo.”


Maybe we should just call it what it is, ADS-B, and remember that “visual contact” is still the gold standard.

The Leap from Out to In

Four years after the ADS-B mandate, the options for both ADS-B In and Out are plentiful, and we are all still finding ways to use it. ATC has embraced the technology, and the pilots flying in the system are pleased with the increased situational awareness and safety provided. The leap from ADS-B Out to ADS-B In is particularly startling. Every pilot I have interviewed has been amazed at just how much traffic they had been missing. Maybe that has been your experience as well.

Fly safe and keep a sharp eye out for traffic!

Editor’s Note: This story originally appeared in the JAN/FEB 2024 issue of Plane & Pilot magazine.


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