Why Some Flights Disappear from Flight Trackers

If you’ve ever searched for a flight on Flightradar24 and found nothing — no icon, no trail, no data — you’ve run into one of aviation tracking’s genuinely complicated problems. Flights not showing on Flightradar24 is one of the most common questions I get from readers, and the answer is almost never simple. I’ve spent years digging into how ADS-B receiver networks actually function, and I still occasionally find edge cases that surprise me. There are at least six distinct reasons a flight can go invisible on a tracker, and most support pages give you one or two at most. This article covers all of them.

No ADS-B Transponder Equipped

This is probably the biggest one. And honestly, I should have opened with this section anyway, because it catches people off guard every time.

ADS-B — Automatic Dependent Surveillance-Broadcast — is the technology that most modern flight tracking is built on. An aircraft with an ADS-B Out transponder broadcasts its GPS-derived position, altitude, speed, and identification continuously. Ground receivers pick that up and feed it to networks like Flightradar24. No ADS-B Out, no tracking. Simple.

Except here’s where it gets complicated. The FAA’s ADS-B Out mandate that took effect January 1, 2020 only applies to aircraft operating in certain controlled airspace — specifically, Class A, Class B, and Class C airspace, plus Class E airspace above 10,000 feet MSL. If a Cessna 172 is puttering around at 3,500 feet in Class G airspace in rural Montana, it is under zero legal obligation to have ADS-B Out installed.

Thousands of small general aviation aircraft still fly with nothing more than a Mode A/C transponder. Mode A gives you a squawk code. Mode C adds pressure altitude. Neither one broadcasts a GPS position. Ground receivers can sometimes derive a rough position from multilateration — triangulating the signal timing across multiple receivers — but that only works when several receivers are close enough to catch the same transmission. Over a small rural airstrip with one receiver 40 miles away, multilateration gives you nothing.

The practical result: a Piper Cherokee on a cross-country flight from a small municipal airport to another small municipal airport may be completely invisible on Flightradar24 the entire time. Not because anything is wrong. Not because the pilot is hiding. Just because the aircraft was built in 1974 and has a Narco AT150 transponder that cost $800 in 1987 and nobody has swapped it out yet.

ADS-B upgrade kits exist — the uAvionix tailBeacon sells for around $1,699, and the Garmin GTX 345 runs closer to $2,500 installed — but retrofitting isn’t free, and for a weekend flyer in uncontrolled airspace, there’s no regulatory push to do it. So the invisibility persists.

Coverage Gaps in the Receiver Network

Ground-based ADS-B reception is entirely line-of-sight. Radio waves don’t bend around mountains. They don’t follow the curvature of the earth. An aircraft flying at low altitude in a mountain valley may be completely below the radio horizon for every receiver within 200 miles. I learned this personally when I tried to track a friend’s Bonanza flying through central Idaho — the aircraft appeared, disappeared for 40 minutes in the Salmon River Mountains, then reappeared near Twin Falls. The flight happened. The data didn’t.

The receiver network is also volunteer-driven for a large part. Flightradar24 has over 35,000 feeding stations globally, contributed by enthusiasts running their own ADS-B receivers — typically a $35 RTL-SDR dongle connected to a Raspberry Pi with a coaxial antenna. Coverage is dense over Europe, the northeastern United States, Japan, and Australia. It gets thin fast over sub-Saharan Africa, central Asia, large parts of South America, and the Canadian north.

Oceans are their own special problem. There are no ground receivers over the Atlantic or Pacific. For oceanic coverage, Flightradar24 and FlightAware both use satellite-based ADS-B — specifically, Aireon’s space-based ADS-B network, which is hosted on Iridium NEXT satellites. That system has genuinely global coverage and can track aircraft over the ocean in near-real-time. It’s why you can watch a British Airways 777 cross the North Atlantic on FR24 without gaps.

ADS-B Exchange, the unfiltered community tracker, does not have satellite ADS-B. Their coverage is entirely ground-based. A flight over the middle of the Pacific will simply not appear on ADS-B Exchange at all, while it shows up fine on Flightradar24. That difference trips people up constantly.

If you want to check where coverage is strong or weak, both Flightradar24 and ADS-B Exchange publish coverage maps. FR24’s is at flightradar24.com/coverage — zoom into any remote area and you’ll see the gaps immediately. ADS-B Exchange has a similar tool. Cross-referencing those maps against where a flight disappeared will usually tell you whether it’s a coverage issue or something else.

Blocked and Filtered Aircraft

Some aircraft are deliberately hidden. This is where the tracking picture gets genuinely interesting from a policy standpoint.

In the United States, the FAA operates a program called LADD — the Limiting Aircraft Data Displayed program. Aircraft operators can request that their registration be blocked from third-party data feeds. The FAA then strips that tail number from the data it provides to commercial tracking services. The aircraft is still flying. It still has a transponder. The FAA still sees it. You just don’t.

LADD is primarily used by corporate flight departments and high-net-worth individuals who don’t want their travel patterns publicly visible. After Elon Musk’s G650ER became a tracking obsession a few years ago, interest in LADD spiked noticeably. A blocked aircraft on Flightradar24 typically shows up as either completely absent or as a generic “Business Jet” with no tail number, depending on whether the operator chose anonymization versus full removal.

Military filtering is handled differently and varies by aircraft type. Most military aircraft simply don’t broadcast ADS-B at all — they use encrypted IFF (Identify Friend or Foe) systems that consumer receivers can’t decode. US Air Force fast movers, for example, are largely invisible by design. Some military transport aircraft and tankers do have ADS-B and show up on trackers intermittently — I’ve tracked KC-135s on ADS-B Exchange on training missions — but this is inconsistent and appears to depend on mission type and command-level policy rather than any published rule.

Foreign military aircraft follow their own countries’ policies. NATO member air forces tend to be fairly opaque. Some non-NATO militaries are surprisingly visible.

How do you tell if a flight is blocked versus simply not equipped? It’s not always obvious, but there are clues. If you know the specific tail number and it’s a modern business jet registered in the US, try looking it up in the FAA LADD database — blocked registrations won’t resolve to a visible aircraft even when you search directly. On ADS-B Exchange specifically, because they do not honor LADD requests, a blocked aircraft will sometimes still appear there when it’s absent everywhere else. That’s a reliable signal that blocking, not equipment or coverage, is the issue.

Why the Same Flight Shows on One Tracker but Not Another

Frustrated by searching for a flight on Flightradar24 and coming up empty, only to find it on ADS-B Exchange thirty seconds later? This happens more than people expect, and the reasons are worth understanding.

Each tracking platform draws on its own receiver network. Flightradar24, FlightAware, and ADS-B Exchange all have independent feeder communities. A receiver that feeds ADS-B Exchange doesn’t automatically feed FR24, and vice versa. In a lightly covered area, one network may have a feeder within range of a flight while the other has nothing. That alone accounts for a significant number of discrepancies between platforms.

Filtering policies differ sharply. Flightradar24 applies LADD blocking, honors various operator requests, and applies its own editorial filters. ADS-B Exchange has a founding philosophy of no filtering — they display everything they receive regardless of who asks them to hide it. This makes ADS-B Exchange uniquely useful for tracking aircraft that have been blocked elsewhere, and it’s why aviation journalists and researchers tend to use it as a primary source when investigating specific flights.

Data delay is another practical variable. Flightradar24’s free tier introduces a delay of approximately 5 minutes for real-time tracking. Their Business subscription, which runs about $99.99 per year, removes that delay. FlightAware’s free tier has similar limitations. ADS-B Exchange shows live data with minimal delay for free. If you’re trying to watch a flight in real time and it seems to be missing on FR24, check whether you’re on the delayed feed first — the aircraft may be exactly where you expect it, just 5 minutes behind.

The practical workflow I use when a flight is missing: check ADS-B Exchange first, because the unfiltered nature and different feeder network makes it the most complete picture of what’s actually being received. If it shows up there but not on FR24, blocking or FR24-specific filtering is the likely culprit. If it’s absent on both, the next step is checking coverage maps for the relevant area. If coverage is good and the aircraft is still missing on both platforms, the transponder equipment is the most probable explanation — either Mode A/C only, or nothing at all.

One more thing worth knowing: helicopter operations, agricultural aircraft, and ultralight operations are particularly likely to be invisible. Ag aircraft fly at extremely low altitudes where line-of-sight coverage is minimal even in well-covered areas. Many ultralights are not certified aircraft under FAR Part 103 and have no transponder requirement whatsoever. The tracking world was built around commercial aviation and has always had blind spots for everything else.

The short version — if a flight isn’t showing on Flightradar24, it’s almost certainly one of six things: no ADS-B equipment, a coverage gap, LADD or military blocking, a different feeder network catchment, a data delay artifact, or an aircraft type that was never really trackable to begin with. Understanding which one applies in a given situation takes a little digging, but the tools to figure it out are all publicly available.