Excellent question. There are several reasons why a flight might not appear on Flightradar24 or similar flight tracking services. The core principle is that Flightradar24 primarily relies on data from the ADS-B (Automatic Dependent Surveillance–Broadcast) system, and any break in that chain of data will result in the flight being invisible or only partially tracked.
Here are the main reasons, categorized:
1. Technical & Regulatory Limitations of ADS-B
- ADS-B Out Not Equipped or Active: Aircraft are required to have an ADS-B transponder in most controlled airspace, but this is not a global universal requirement. Many older aircraft, military planes, small private aircraft, and aircraft in certain regions may not be equipped or may have it switched off.
- Out of Ground Station Coverage: Flightradar24’s network of over 40,000 ADS-B receivers is vast, but there are still gaps, particularly over oceans, remote deserts (Sahara, Outback), and polar regions. In these areas, flights can disappear until they come within range of another receiver.
- Satellite-Based Tracking is Limited: While Flightradar24 does supplement with some satellite data (from Aireon and others), this is not available for all flights globally. Their primary, free-to-view service is ground-station based.
2. Intentional Blocking or Filtering
- Military & Government Flights: Most military aircraft (Air Force One, fighter jets, surveillance planes) do not broadcast ADS-B publicly for operational security, or they use a masked/encrypted mode. They may appear only as a generic “BLOCKED” tag or not at all.