Watching a flight crawl across a map on your phone feels effortless, but the technology behind it is a layered mix of decades-old radar ideas, a clever radio broadcast system, and now satellites in low Earth orbit. The Simple Flying Flight Tracker draws on all of it, and understanding the basics makes those smooth-looking flight paths a lot more interesting.
It starts with the old stuff. Primary radar — the spinning dishes most people picture — bounces radio waves off an aircraft's body to work out where it is. Useful, but it can't tell you what the plane is, how fast it's climbing, or where it's headed. Secondary surveillance radar added the transponder, a device on the aircraft that answers ground interrogations with its altitude and a four-digit squawk code. Modern Mode S transponders broadcast richer data on a dedicated 1,090 MHz frequency, including emergency codes like 7700 for a general emergency or 7600 for radio failure, picked up by receivers within roughly 200 nautical miles.
The real game-changer is ADS-B — Automatic Dependent Surveillance-Broadcast. Instead of waiting to be pinged, the aircraft works out its own position via GPS and broadcasts its latitude, longitude, altitude and speed about once per second, unencrypted, to any receiver in line of sight. A jet at cruising altitude can be heard over 250 nautical miles away. Networks like Simple Flying's harvest these bursts from thousands of ground receivers — a basic unit costs under $200 to build — and cross-check timestamps from multiple stations to filter out bad data.
Ground receivers have limits, though: signals travel in straight lines and can't bend around the Earth's curvature, so aircraft behind mountains or over oceans drop off the map. Trackers handle short gaps with dead reckoning, projecting the plane's path from its last known position, speed, heading and descent rate until contact resumes. The big fix for oceans is space-based ADS-B: companies like Aireon host receiver payloads on the Iridium NEXT satellite constellation, listening for the same broadcasts from orbit. Now a widebody crossing the North Atlantic stays visible in near-real time, a safety leap that has eased the old oceanic separation rules and means search-and-rescue teams get precise telemetry even if a crew squawks 7700 far from land.
There are growing pains. GPS jamming and spoofing are on the rise, so tracker platforms flag erratic or unusual data rather than taking every broadcast at face value. Regulators like the FAA and Eurocontrol have made ADS-B mandatory in controlled airspace, and AI-driven predictive models are on the way — anticipating turbulence, optimising routing and smoothing airport arrivals.
For travellers, this matters more than it might seem. Whether you're picking someone up at arrivals, tracking a delay, or just plane-spotting from the sofa, the accuracy of that moving icon rests on a global mesh of $200 DIY receivers and orbiting satellites. It's one of aviation's most underappreciated upgrades: a commercial flight now essentially never flies out of sight.
