Spy Planes on Flightradar24: How ADS-B Tracking Exposes the RC-135

by Tamika Johnson | Sep 27, 2026 | Mondo dell'aviazione, Aviazione militare | 0 comments

Open a flight-tracking app on almost any day and look at the Black Sea or the Baltic. Among the airliners you will often find something that does not belong: a four-engined jet flying long racetrack patterns off a coastline, or a drone orbiting at 50,000 feet for most of a day. They are spy planes, and anyone with a phone can watch them.

It seems like a contradiction. Why would an intelligence-gathering aircraft broadcast its own position to the world? The answer lies in a technology called ADS-B, in the rules of international airspace, and in a network of tens of thousands of enthusiasts' receivers.

Informazioni rapide

ADS-B: Automatic Dependent Surveillance-Broadcast: the aircraft broadcasts its identity, position, altitude and velocity
Frequencies: 1090 MHz Extended Squitter for most aircraft; 978 MHz UAT for some US general aviation
US mandate: Required in most controlled US airspace since 1 January 2020
MLAT: Multilateration: locating aircraft without ADS-B position data from the timing of their transponder signals at several receivers
Flightradar24 network: More than 50,000 receivers on seven continents and in space, according to the company
Encryption: None: ADS-B signals are unencrypted and can be received by anyone

How ADS-B Gives the Game Away

ADS-B is simple. An equipped aircraft works out its position from satellite navigation and broadcasts it automatically, along with its identity, altitude and speed, with no action from the pilot. Air traffic control uses the data, and so do other aircraft. So does anyone else with a cheap receiver and an antenna, because the signals are not encrypted.

Flight-tracking services such as Flightradar24 collect these broadcasts from volunteers' receivers around the world. For aircraft whose transponders send an identity but no position, they use multilateration: several receivers note the precise moment the same signal arrives, and the differences in timing reveal where the aircraft is. Many military aircraft fall into this category, according to Flightradar24, because they carry Mode S transponders that send less data.

Flightradar24 explains how ADS-B tracking works. Video: Flightradar24

Why Spy Planes Switch Their Transponders On

Reconnaissance aircraft such as the RC-135 usually fly in international airspace, often through busy airline corridors. Broadcasting their position lets air traffic controllers and airliners see them and keep their distance. According to The Aviationist, that safety and deconfliction role, under the principle of due regard in international airspace, is why military aircraft transmit at all.

Crucially, switching the transponder on gives little away to an adversary. The country being watched tracks these aircraft on its own radar anyway, with or without ADS-B. The people who learn most from the broadcasts are the public and the open-source intelligence community.

RAF RC-135W Rivet Joint ZZ664 — Royal Air Force RC-135W Rivet Joint ZZ664. The RAF's Rivet Joints regularly appear on public flight trackers when they fly over the Baltic and the Black Sea. Photo: Wikimedia Commons, CC BY 2.0

The Hex Code Affair

Not every broadcast is what it seems. On 7 September 2020, during a mission near China's Hainan island, a US Air Force RC-135W transmitted a Malaysian aircraft's hex code instead of its own, according to The Aviationist. It caused a stir online, but the change made no difference to Chinese air defences, which identify aircraft by radar, flight plans and track history, not only by transponder codes.

“There is ZERO operational advantage, repeat ZERO advantage in doing this.”

Robert Hopkins — former RC-135 aircraft commander, quoted by The Aviationist

Hopkins suggested the only audience such tricks confuse is the amateur tracking community, and argued the practice was counterproductive.

“It only serves to undermine a legitimate and safe operation in international airspace.”

Robert Hopkins — former RC-135 aircraft commander, quoted by The Aviationist

What the Trackers See

When Russia invaded Ukraine in 2022, Flightradar24 published a guide to the military traffic its users were watching around the country: RQ-4 Global Hawk drones under the callsign FORTE flying distinctive patterns over the Black Sea at more than 50,000 feet, RAF RC-135s from Waddington near Ukraine's western border and Belarus, NATO E-3 AWACS, tankers and transports.

RQ-4 Global Hawk in flight — An RQ-4 Global Hawk. Drones of this type flying as FORTE became some of the most watched aircraft on public flight trackers over the Black Sea. US Air Force photo / Wikimedia Commons, public domain

The watching continues. On 25 September 2026, UK Defence Journal reported, based on Flightradar24 data, that both of the RAF's operational Rivet Joints had flown intelligence missions at the same time, one around the Baltic and Kaliningrad and one over the Black Sea. Specialist sites such as ItaMilRadar track the same aircraft day by day. What was once secret is now, at least in outline, a matter of public record.

The Canada Aviation and Space Museum explains ADS-B in two minutes. Video: Canada Aviation and Space Museum

What the Trackers Do Not See

There are limits. Aircraft can fly with their transponders off, and many military missions do. Flight trackers show where an aircraft is, not what it is doing. And privacy programmes such as the FAA's LADD scheme can hide some aircraft from tracking websites, though because ADS-B is unencrypted, the raw data can still be received by anyone listening.

So the next time you spot a lonely jet circling off a coastline on your flight-tracking app, you may be looking at a spy plane at work. It is visible because its crew want other aircraft to see them. What it is listening to stays secret.

Captain Joe on ADS-B and the future of aircraft surveillance. Video: Captain Joe

Sources: Flightradar24, Wikipedia (ADS-B), The Aviationist, UK Defence Journal

Domande frequenti

How can I see spy planes on Flightradar24?

Many military reconnaissance aircraft, such as RC-135 Rivet Joints and RQ-4 Global Hawks, fly with transponders switched on in international airspace. Flight trackers like Flightradar24 pick up their ADS-B or Mode S signals through volunteer receivers, so the aircraft appear on the public map.

Why do military spy planes turn on their transponders?

Military aircraft broadcast on Mode S or ADS-B mainly for safety and deconfliction with civilian traffic in international airspace. It gives little away to an adversary, which tracks them on its own radar anyway, but it lets airliners and air traffic control see them.

What is ADS-B?

ADS-B, or Automatic Dependent Surveillance-Broadcast, is a system in which an aircraft automatically broadcasts its identity, position, altitude and velocity. It uses 1090 MHz Extended Squitter or 978 MHz UAT, and it has been mandatory in most controlled US airspace since 1 January 2020.

What is MLAT in flight tracking?

MLAT, or multilateration, locates aircraft that transmit Mode S transponder signals without position data. Several ground receivers record the exact time the same signal arrives, and the differences in arrival time are used to calculate the aircraft's position. Many military aircraft are tracked this way.

Did a US spy plane use a fake identity?

On 7 September 2020 a US Air Force RC-135W near Hainan transmitted a Malaysian hex code instead of its own, according to The Aviationist. It did not hide the aircraft from Chinese radar; former RC-135 commander Robert Hopkins said the practice offered zero operational advantage.

Can aircraft hide from flight tracking websites?

Yes, to a degree. Aircraft can fly with transponders off, and programmes such as the FAA's LADD can block some aircraft from tracking sites. But because ADS-B signals are unencrypted, anyone with a receiver can still pick up an aircraft that is transmitting.