ADS-B Off: Why Aircraft Stop Broadcasting, and What Their Silence Tells You

There is a habit, in aerial OSINT, of treating ADS-B coverage gaps the way maritime analysts treat AIS gaps. The analogy is useful but incomplete. Aircraft transponders behave differently. They fail differently. And, importantly, the legal regime around them is much stricter.

Above 18,000 feet in U.S. airspace, ADS-B Out is mandatory. In European Single Sky, it is mandatory above a similar threshold. Russia and parts of Central Asia are weaker. The Gulf is mostly compliant. Switching the transponder off is, in most regimes, a deliberate decision with a paper trail at ATC level.

The four kinds of "off"

In our investigations we see four patterns. They look identical at first glance and behave nothing alike.

• Receiver-side blackout. The aircraft is broadcasting. No receiver hears it. Common over the Greenland gap, the Pacific north of Hawaii, and parts of the Sahara. Boring.
• Transponder failure. Genuine hardware fault. Crew declares it, ATC routes them lower, the aircraft reappears within minutes once the spare unit is online. Very short gap, often correlated with a brief altitude drop.
• Privacy block (LADD / FAA Privacy ICAO Address). The aircraft is broadcasting, the receiver hears it, but the ICAO hex is rotated or filtered by aggregators. This is administrative invisibility, not technical. It leaves fingerprints.
• Deliberate switch-off. Crew turns the transponder to standby or off. Illegal in most controlled airspace. Rare. Memorable.

Telling them apart is the whole game. A receiver-side blackout has consistent geography across many aircraft on the same day. A privacy block is a single aircraft whose hex changes, but whose route stays correlated to a known operator. A deliberate switch-off is a clean signal until a precise moment, then silence, then a clean re-emergence — often hours later, often over different terrain.

The case that taught us the difference

A few months back we were tracking the movement of a Boeing 737 BBJ registered to a holding company in a friendly jurisdiction. The aircraft had been making regular runs between two Gulf capitals. Then, on a Tuesday afternoon, it took off from the eastern Mediterranean, climbed to FL410, and disappeared somewhere over central Turkey.

The blackout lasted six hours. When the aircraft reappeared, it was descending into a third-country airport. Its hex code was the same. Its operator was the same. Its callsign was the same. The fuel consumption was consistent with a single straight-line flight, not a stopover.

That is what you might call a deliberate switch-off. Nothing about the receiver geography supported a coverage explanation — Anatolia is a well-covered area. Nothing about the flight envelope supported a failure — the aircraft was flying perfectly. Cross-referenced against the holding company's beneficial-ownership filings (one Sentinel pivot away from an OFAC SDN entity), the picture filled in fast.

What to do with the lead

A clean ADS-B blackout is not, on its own, a story. It is a lead. The next questions are:

• Who owns the aircraft? Not the holding company on the registry — the actual ultimate beneficial owner.
• Where did the aircraft go? Fuel range, weather, and re-emergence geometry usually narrow this to one or two airports.
• Who else moved at the same time? Sanctions-watch lists are full of people who travel quietly. If a UBO appears in a city the same evening, that is no longer a coincidence.
• What was on the other end? Some destinations are themselves the story.

This is the kind of pivot that the Sentinel entity engine was built for. Aircraft to owner, owner to corporate chain, corporate chain to sanctioned individual, sanctioned individual to other movements. The trick is keeping the chain short and the citations clean. A brief that travels with its sources is a brief an editor publishes.

A note on ethics

Aerial OSINT, more than maritime, has a privacy dimension. Most aircraft tracked have nothing to do with sanctions or geopolitics — they belong to people exercising their lawful right to fly. The discipline is to focus the work on aircraft whose ownership chain is itself a public-interest story: sanctioned entities, kleptocratic networks, conflict actors. The receiver hears everyone. The analyst chooses who matters.