ADS-B Flight Tracking on iPhone: What It Is and How to Use It
If you've ever used a flight tracking app and wondered how it knows where every plane is in real-time, the answer is ADS-B. This technology underpins all consumer aircraft tracking — and understanding it helps you get more out of every app you use.
What Is ADS-B?
ADS-B stands for Automatic Dependent Surveillance-Broadcast. It's a surveillance technology used in aviation where aircraft continuously broadcast their position and status data, which can be received by ground stations and other aircraft.
There are two components:
- ADS-B Out — the aircraft transmits its GPS position, altitude, speed, heading, and a unique identifier (the ICAO hex code) automatically, without any input from the crew
- ADS-B In — some aircraft (and ground stations) receive ADS-B transmissions from nearby aircraft, giving a traffic picture without needing radar
ADS-B operates on 1090 MHz (the Mode S extended squitter format) used by commercial aviation worldwide, and 978 MHz (UAT, used primarily in the US for general aviation below 18,000 feet).
Why ADS-B Is Better Than Radar
Traditional radar determines aircraft position by sending out radio pulses and measuring the reflected signal. It's reliable but has limitations:
- It requires expensive ground infrastructure
- It has blind spots, especially in mountainous or remote areas
- It only gives position, not aircraft identity (without secondary radar)
- Updates are relatively slow — typically every 4–12 seconds
ADS-B, by contrast:
- Updates every 0.5–1 second
- Is self-reported — no radar infrastructure needed
- Includes aircraft identity, type, and precise GPS altitude automatically
- Has global coverage when combined with satellite-based ADS-B receivers
This is why consumer flight tracking apps are able to show live, accurate aircraft positions — they're aggregating ADS-B data from thousands of volunteer-operated ground receivers.
How ADS-B Tracking Works in Apps
Networks like adsb.lol (which powers What Plane?) aggregate data from a distributed network of ground-based ADS-B receivers. When you open a tracking app on your iPhone:
- The app reads your GPS location
- It queries the ADS-B network for aircraft transmitting within a set radius of your position
- The returned data includes position, altitude, speed, heading, flight number, and aircraft type
- The app enriches this with additional data — airline logos, aircraft model images, route information — from supplementary databases
The result is a near real-time picture of the sky above you.
Coverage Limitations
ADS-B ground receivers need line of sight to aircraft transponders. This means:
- High-altitude cruise flights are almost always covered — the elevation angle means a single receiver can hear aircraft hundreds of miles away
- Low-altitude aircraft may disappear from coverage in areas with poor receiver density — rural areas, mountainous terrain
- Oceanic flights are tracked via satellite-based ADS-B receivers (Aireon's network, integrated into services like Flightradar24's premium data)
- Military aircraft generally do not broadcast ADS-B on public frequencies, or broadcast limited data
- Some private jets are filtered from public displays at the owner's request
For the UK and most of Europe, ADS-B coverage is excellent at all altitudes, including final approach and ground movement at major airports.
ADS-B on iPhone: What Plane?
What Plane? is a native iPhone app that uses ADS-B data from adsb.lol to give you instant access to what's overhead. What sets it apart from other ADS-B apps:
Home Screen Widget
The widget shows the nearest aircraft passively — airline, type, altitude, speed, distance, and a compass ring bearing that shows the aircraft's direction relative to you. You don't need to open the app; the answer is on your home screen.
Zero Clutter
Most ADS-B apps present data as a radar-style map with dozens of flight icons, which is great for getting a global picture but poor for quickly identifying the one plane you can hear above you. What Plane? prioritises the nearest aircraft and presents it cleanly.
Rich Aircraft Data
Each aircraft entry shows:
- ICAO aircraft type code and full name
- Airline livery rendered on an accurate 3D-style model
- Origin and destination
- Live altitude, ground speed, and distance
- Bearing indicator
Full Nearby Traffic
Browse all aircraft within 30 nautical miles, sorted by distance. Useful at busy times when multiple aircraft are stacked on approach.
What Is ICAO Hex Code?
Every ADS-B-equipped aircraft has a unique 24-bit ICAO address, shown in hexadecimal (e.g. 400934). This is permanently assigned to the aircraft's transponder — unlike flight numbers, which change with every route. Enthusiasts use these codes to identify and track specific aircraft over time, building records of where a particular airframe has been.
Getting Started
Ready to explore ADS-B on your iPhone? Download What Plane? and allow location access. Within seconds, you'll see the nearest aircraft with full ADS-B data — all without needing to understand a single line of transponder code.
Free on the App Store. No ads, no subscription.
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Ready to identify planes instantly? Download What Plane? on the App Store →