Why an aircraft doesn’t show up on Flightradar: the most common reasons

The jet is just taxiing to the runway, you can even see the registration on the tail – and in the flight tracker app there is nothing at that spot. Or a tanker audibly circles over the region without any map showing it. Anyone who spots regularly knows this. The question of why an aircraft doesn’t show up on Flightradar has a surprising number of answers: deliberate filters, privacy programs, gaps in the receiver network, military operations or simply an aircraft that transmits no position at all. This guide sorts out the causes and shows you how to find out at the spot which one applies right now.

The short answer

Flight tracker services such as Flightradar24 do not operate radar stations of their own. They show what the aircraft itself transmits and what a receiver picks up. An aircraft is therefore missing from the map if at least one of three conditions is not met:

1. The aircraft transmits usable data, ideally an ADS-B position.
2. A receiver hears the signal, on the ground or by satellite.
3. The service displays the data instead of filtering or anonymizing it.

Almost every case can be assigned to one of these three stages. How the chain works technically is explained in detail in the basics article Flight tracking with ADS-B for spotters.

Cause 1: the service filters deliberately

The big commercial services hide part of the traffic or show it only anonymously. Flightradar24 justifies this with security and privacy and names the US LADD program and other programs. A well-known example: a Japanese government aircraft was visible there until 2014, then the Japanese Ministry of Defense had it blocked.

LADD: the FAA’s blocking program

LADD stands for Limiting Aircraft Data Displayed. Through this program of the US aviation authority FAA, owners or their representatives can request that the flight data of their aircraft not appear publicly. Services that obtain data from the FAA commit to implementing these blocks. Mainly affected are business and private aircraft with US registrations.

What matters for spotters: LADD acts on the display, not on the signal. The aircraft keeps transmitting unencrypted, and receivers outside the FAA data stream pick it up just like any other. That is why LADD aircraft often show up on unfiltered maps, while Flightradar24 or FlightAware hide them or show them only as an anonymous type.

Blocks at the request of owners and authorities

Besides LADD there are blocks agreed directly with the service, for example by owners, governments or the military. How the individual services handle this differs. Some show nothing at all in place of the aircraft, others only position and type without registration and without flight history. An overview of which service filters how is given in the flight tracker app comparison, and Flightradar24 vs. FlightAware compares the two big providers.

Cause 2: PIA – visible, but without a name

A special case is PIA, the Privacy ICAO Address. Every Mode S transponder transmits a fixed 24-bit address (hex code), through which databases can normally determine the registration. Eligible owners in the US can instead request a temporary address that is not assigned to them in the public registry. A callsign from an approved third-party provider is added, at FlightAware for example with the prefix FWR.

The result: the aircraft appears on the map, but with an unknown address and a neutral callsign. Even an unfiltered map cannot automatically match it to a registration. You then see a business jet without an identity. At the fence that is no problem – the registration is on the fuselage after all. How to log such a sighting properly afterward is shown in the guide Tracking an aircraft by registration or hex code. Why business aircraft in particular are so often affected is explained in Spotting business jets.

Cause 3: no receiver hears the signal

By far the most common cause is mundane: nobody receives the aircraft. The signal on 1090 MHz travels in a virtually straight line. A receiver therefore needs line of sight to the aircraft. That produces typical gaps:

• Close to the ground: An aircraft that is taxiing or has just landed is only seen by a receiver in the immediate vicinity. If there is no feeder at the airport, the track often ends on final approach.
• Terrain: Valleys, mountains and hills shadow low-flying aircraft even if receivers are not far away.
• Sparsely populated regions: The networks consist largely of volunteers with receivers on their roofs. Where few people live, there are few feeders.
• Oceans: Over the open sea there are no ground receivers; only satellite reception helps there. Since March 2020, Flightradar24 shows satellite positions to all users; they are marked blue instead of yellow there. What the colors and symbols mean is explained in Flight tracker symbols and colors.
• Outages: If a single receiver at the airport fails, all the taxi traffic suddenly disappears.

Cause 4: the aircraft transmits no position

Even with perfect coverage, everything depends on what is installed on board. You should distinguish four levels:

Equipment	What is transmitted	On the map
Mode S with ADS-B	Address, position, altitude, speed, flight identification	visible as soon as a receiver is in range
Mode S without ADS-B	Address and altitude, but no position	only with multilateration (MLAT), otherwise not
Mode A/C	Squawk code and altitude, no unique address	practically not
Transponder off or not installed	nothing	not

ADS-B mandate: who has to transmit and who does not

In Europe, an ADS-B Out mandate applies to flights under instrument flight rules for aircraft with a maximum takeoff mass of more than 5,700 kg or a maximum cruising speed above 250 knots; the rule has applied since 2020, with exceptions for state aircraft, for example. In the US, ADS-B Out has been required in certain airspace since January 1, 2020. Smaller aircraft, gliders, balloons and many helicopters are often not covered in Europe.

For you that means: an airliner is rarely missing because of missing equipment. For small aircraft, vintage aircraft and helicopters, on the other hand, it is the normal case. Typical candidates are introduced in Recognizing small aircraft, and for rescue and police helicopters there are separate tips in Finding helicopters on the flight tracker.

MLAT to the rescue – with limits

If an aircraft transmits Mode S without a position, the network can calculate it by multilateration: several receivers measure when the same signal arrives at them, and the server determines the location from that. As a rule of thumb, that takes four receivers that hear the aircraft at the same time. In metropolitan areas this works well, but close to the ground and at the edge of the network the track breaks off much earlier than with ADS-B. The details are in MLAT explained, the transponder types in Mode S transponders explained.

Gliders and many light aircraft also transmit FLARM. Some services evaluate this, but only over a short range. More on this in Receiving FLARM and OGN.

Cause 5: military and state flights

Military traffic is a special case in which several causes come together:

• Transponder off or restricted: On missions and during exercises, many military aircraft transmit no data or only limited data. What does not transmit is on no map.
• No ADS-B: Many military aircraft transmit Mode S without a position. They only become visible where MLAT works.
• Exemptions for state aircraft: The European ADS-B mandate contains special rules for state aircraft.
• Filtering: Commercial services hide individual military and government flights on request.

On unfiltered maps such as ADS-B Exchange or the community trackers adsb.fi and adsb.lol you therefore see considerably more transports, tankers and reconnaissance aircraft, for example a Boeing E-3 Sentry in the exercise area or an Airbus A400M on a ferry flight. How to search specifically for such flights is described in Tracking military aircraft online. For government aircraft such as those of the Flugbereitschaft BMVg (the German Federal Ministry of Defense’s air transport wing), the guide Spotting government aircraft is worth reading.

Other reasons you should know

Besides the big five, there are a few smaller effects that regularly confuse spotters:

• Delayed data sources: In the US, Flightradar24 fills gaps with FAA data that is delayed by about five minutes and partly contains no registration. The aircraft is then already above you while the map still shows it far out.
• Wrong or missing flight identification: If the crew did not enter the callsign correctly, you will not find the flight by flight number, but you will by registration. The difference is explained in Callsign and flight number.
• Filters in the app: Depending on the settings, many apps hide ground traffic, gliders, certain altitudes or data sources. A look at the filter settings solves many a puzzle. Operation is shown in the Flightradar24 guide.
• New or re-registered aircraft: If the address is missing from the service’s database, the aircraft appears without registration and type or is not found when searching.

How to find the cause at the spot

With a few steps you narrow down why an aircraft is missing.

The follow-up is described in Matching sightings with ADS-B logs. Anyone with permanent gaps at their home airport can close them themselves: with a receiver of your own, as described in Building your own ADS-B receiver, you improve coverage for everyone – or you take a small receiver along to the spot, see Mobile ADS-B reception at the spot.

What to keep in mind

• The map is a hint, not a guarantee. An empty sky on the display does not mean nothing is coming – especially with rarities.
• Filtered does not mean secret. An aircraft that is missing on one service is not automatically “forbidden” to photograph. The usual rules from Is plane spotting allowed? apply.
• MLAT positions jump. Calculated tracks are somewhat less accurate and arrive slightly delayed. For the question of whether an aircraft is about to arrive, they are good enough.
• Emergency squawks are not a destination for an outing. If an aircraft stands out with a code from Squawk 7500, 7600 and 7700, keep rescue routes clear.

Conclusion

When an aircraft is missing on Flightradar, there is almost never a secret behind it, but a gap in the chain of transmitting, receiving and displaying. Commercial services filter deliberately, for example through LADD. PIA makes US aircraft anonymous without hiding them. Most often, though, coverage is simply missing, above all close to the ground. Small aircraft and military aircraft often transmit no position and are visible only by MLAT or not at all. Anyone with a second service and an unfiltered map ready usually finds the cause quickly – and the registration on the fuselage is only there at the fence anyway.