Why ADS-B Out Is Required but Not Everyone Has It

The 2020 Mandate and What It Actually Covered

Aircraft tracking has gotten complicated with all the misinformation flying around. As someone who spent the better part of last year obsessing over disappearing blips on flight trackers, I learned everything there is to know about ADS-B compliance gaps. Today, I will share it all with you.

On January 1, 2020, the FAA flipped a switch that changed how we follow planes across the sky. Every aircraft operating in certain airspace had to carry ADS-B Out — a transponder system broadcasting GPS position, altitude, velocity, and identification data 15 times per second. Sounds clean, right? Mandate drops, everyone equips, trackers light up. Reality proved messier.

The rule applies to Class B airspace around major airports, Class C around mid-sized ones, Class E above 10,000 feet mean sea level, and chunks of Class D. Stay below 10,000 feet in uncontrolled airspace and never brush a Class B or C boundary? You weren’t forced to upgrade. That carve-out matters — a lot.

The FAA regulates roughly 350,000 active general aviation aircraft across the United States. The 2020 rule wasn’t even new — it was first proposed back in 2007, then delayed repeatedly for over a decade. Operators had been bracing for it for years. When the deadline finally hit, not everyone had complied. Some never would.

Which Aircraft Are Still Legally Flying Without It

Frustrated by a Cessna 172 that kept vanishing from Flightradar24 mid-flight last August, I tracked down the pilot directly using tail number N8842V and a cold email. He explained he was exempt — legally, entirely above board. That 20-minute phone call taught me something important: exemption and rarity are not the same thing.

Here’s who doesn’t have to equip:

• Aircraft operating only in Class G airspace. Uncontrolled airspace below 1,200 feet AGL in populated areas, or below 10,000 feet in rural zones. Plenty of bush pilots, ag operators, and weekend recreational flyers never leave Class G. Ever.
• Pre-1978 piston aircraft with certain avionics configurations. The FAA carved out a grandfathering exemption for vintage planes running Mode C or Mode S transponders without certain modern avionics. Got a 1977 Beechcraft Bonanza with the right transponder setup? You’re covered.
• Gliders. Motorized or not — fully exempt from ADS-B Out requirements.
• Balloons. Same exemption. They still file flight plans and operate safely. They just don’t broadcast continuously.
• Ultralights and experimental aircraft. Different regulatory frameworks entirely.
• Aircraft that stopped flying before 2020. A plane sitting in a hangar in Bozeman collecting dust isn’t required to upgrade. It still counts in the FAA registry even if it hasn’t left the ground since 2019.

The numbers are staggering. The FAA estimated roughly 150,000 general aviation aircraft would qualify for exemption. One hundred fifty thousand. That’s not a fringe group — that’s 42 percent of the active fleet. Many are legitimate, well-maintained aircraft operating exactly as the regulations allow.

Why Compliance Numbers Are Still Below 100 Percent

Probably should have opened with this section, honestly. The compliance gap isn’t a mystery once you account for cost and logistics.

An ADS-B Out system runs between $3,000 and $15,000 installed — depending on avionics complexity and aircraft type. For the owner of a $40,000 Cessna 172, that’s a brutal hit. I know a flight school operator outside Scottsdale who delayed upgrading three trainer aircraft for 18 months because the math simply didn’t work. Those planes would be retired before the equipment paid for itself. Don’t make my mistake of assuming every non-equipped aircraft is a compliance failure — sometimes it’s just economics.

Avionics shops experienced crushing backlogs through 2019 and into 2020. I tracked one shop’s booking calendar in Phoenix during February 2020. Booked out six months solid. Owners who genuinely wanted to comply couldn’t get appointments. By the time capacity opened up, January 1st had already come and gone.

Some aircraft just stopped flying altogether. Owners of vintage taildraggers, experimental builds, or barely-airworthy projects let their certificates lapse or deferred annual inspections indefinitely. Ground a plane before the deadline and you’ve avoided the upgrade cost entirely. The FAA can’t compel owners to fly aircraft they’ve decided to park.

Then there’s the international and waiver category. Some aircraft operate under FAA exemptions or special flight authorizations, or they enter US airspace from bases abroad where ADS-B requirements differ. These aren’t scofflaws. They’re operating under explicit, documented permission. They just won’t show up cleanly on consumer trackers.

What This Looks Like on a Flight Tracker

But what is the actual user experience here? In essence, it’s a layered data problem. But it’s much more than that.

When you’re watching Flightradar24, FlightAware, or ADS-B Exchange, you’re seeing multiple data sources stitched together in real time. ADS-B Out equipped aircraft appear with near-perfect precision — position updating 15 times per second, call signs, altitudes, speeds. No lag. No guessing.

Aircraft without ADS-B Out can still appear, but only if they’re running Mode C or Mode S transponders and flying within range of ground-based receiver coverage. That method is called multilateration — MLAT. It works by calculating position from time-of-arrival differences of a transponder signal across multiple receivers. Clever system. Not dense everywhere. Rural Montana has thin coverage. Parts of the Gulf have essentially none.

If an aircraft is in Class G airspace under visual flight rules without any transponder, it won’t appear on any public tracker. That’s not a system failure — it’s working exactly as designed. VFR in uncontrolled airspace simply doesn’t require a transponder.

The confusing middle ground is the biggest source of questions I see posted in aviation forums every week: a plane visible yesterday just vanished today. Usually it wasn’t ADS-B equipped to begin with — you were seeing it via MLAT, which cuts out over water or in coverage gaps. Or it descended below 10,000 feet and left controlled airspace entirely. Legal. Normal. Just gone from your screen.

Will the Coverage Gap Ever Close

The gap will shrink. It won’t disappear. And honestly — that’s okay.

I’m apparently a budget-avionics nerd, and uAvionix works for me while legacy panel systems never make financial sense for experimental builds. Their portable and experimental-category units run $500–$2,000 depending on configuration, which is a far cry from a $12,000 Garmin install. More owners are retrofitting older aircraft with these budget options every year. That’ll push equipped percentages higher over time.

The FAA continues reviewing whether to expand the mandate to currently exempt aircraft. A future rule might close the Class G loophole for certain aircraft types or drop the altitude threshold. Regulatory cycles move slowly though — we’re talking years, not months. Don’t hold your breath waiting on that one.

What matters right now is understanding what you’re actually seeing when you pull up a flight tracker. Non-equipped aircraft aren’t breaking the law. They’re not mysteriously vanishing. They’re flying legally, often in airspace where continuous tracking was never required. That’s what makes this whole system endearing to us aviation nerds — the complexity is baked in intentionally, not accidentally.

So, without further ado, here’s the bottom line: the 2020 mandate did exactly what it was designed to do. It put ADS-B Out into the cockpits of pilots operating in busy, controlled airspace where surveillance matters most. The exemptions exist for genuine operational and economic reasons. The coverage gap reflects a deliberate tradeoff — not a compliance failure, not a ghost in the data.