ADS-B · coverage and limits
A missing track is not an empty sky
An ADS-B map represents messages received by a network, decoded and then published. It is neither exhaustive radar nor a register of every mission in progress.
- Published
- Revised
From aircraft to screen
The signal must clear terrain, reach a receiver, pass through the aggregator and arrive in time for the snapshot. Failure at any one stage removes the point.
Short answer
An aircraft can be missing because its signal reaches no receiver, especially at low level behind terrain; because its equipment or message does not provide a usable ADS-B position; because the network filters, delays or loses data; or because the map follows only a defined catalog. Absence on screen cannot establish absence in the real world.
Key points
Radio follows line of sight
At low altitude, a ridge or terrain curvature can stop reception only a few miles away.
Mode S is not always a position
A transponder may be detected without broadcasting every field needed for a geographic point.
The site shows what it received
Fire Maps preserves provenance and never fills a gap with an invented position.
Coverage depends on radio geometry
Ground-received ADS-B transmissions travel mainly by line of sight. The higher an aircraft is, the wider its radio horizon. A helicopter in a valley or an airtanker descending behind a ridge can disappear from a network while continuing to fly.
Receiver density varies by region. A city or plain may be heard extremely well; mountains, a remote coast or a sparsely equipped region may have lasting gaps.
Not every signal contains the same information
ADS-B means the aircraft broadcasts data including a position calculated onboard. Mode S more broadly identifies a transponder mode: some messages identify an address without directly supplying a complete usable position.
Equipment, configuration, local requirements, failure and operational decisions can change what is transmitted. A civil map must not assume missing fields.
Data can be lost between the antenna and the map
A receiver timestamps and forwards messages; an aggregator deduplicates them; an API builds a snapshot; the site caches it. An outage, delay or filtering policy at any stage can create a missing segment.
Fire Maps archives positions that were actually received. A line between two points does not prove the exact path between them, and no algorithm turns radio silence into a measurement.
How to read a track gap honestly
Check the last point time, altitude, terrain, stated coverage and whether the track resumes. A gap as an aircraft descends behind a ridge is compatible with lost reception; it is not proof of a mission.
For safety decisions or official information, use the responsible authorities and operational services. A public map is an observation aid, not an air-traffic separation system.
Common questions
- Does disappearance mean the pilot switched off the transponder?
- No. That is one possibility among many and cannot be inferred from a gap alone. Terrain, altitude, receivers, network transport and filtering are common explanations.
- Is the straight line between two points the real path?
- No. It connects two observations. The longer the interval, the less it describes what happened between them; turns, orbits and altitude changes may be missing.
- Can a Mode-S address be derived from a registration?
- It must never be guessed. A wrong address can silently attach a sheet to the wrong aircraft. Fire Maps catalogs only cross-checked matches.
Primary sources consulted
Revised · July 29, 2026