How it works

From a transponder squitter to "look southwest, twenty degrees up."

Overflight identifies overhead aircraft by combining three things: live transponder data from a volunteer receiver network, a visibility model that knows what a human eye can plausibly see, and your position, including how high you're standing. This page walks through each.

Data

Where the aircraft come from

Nearly every airliner, and most other powered aircraft, continuously broadcasts its position, altitude, speed, and identity over ADS-B on 1090 MHz. Volunteers around the world run small receivers that pick these broadcasts up and pool them. Overflight queries one of these pools, the airplanes.live network, for the traffic around your coordinates every few seconds. No account, no API key on your device.

It misses what isn't broadcasting: aircraft without ADS-B (some general aviation, gliders before FLARM bridges, and military traffic with transponders dark) won't appear. What you see is what's being broadcast and received. In practice, near any populated area, that's nearly everything in the sky.

Visibility

Deciding what you can actually see

A flat "everything within 25 miles" circle is the easy answer and the wrong one. Whether you can see an aircraft depends on slant range along your sight line and on what the aircraft is. A 777 at cruise is visible from extraordinary distances; a Skyhawk in the pattern disappears a few miles out. Overflight holds a per-class table of clear-day visual horizons and tests every contact against it.

Your own elevation matters too. A jet at 15,000 feet is much more "overhead" from a Colorado ridge at 8,000 feet than from a beach. The model works from each aircraft's height above you, not above sea level, using your GPS altitude or, where that's missing, a terrain lookup from Open-Meteo.

The RANGE setting, with NEAR, NORMAL, and FAR positions, scales this whole model up or down rather than swapping the circle for a bigger circle.

Geometry

Which way to look

For the aircraft in focus, Overflight computes the look line from your position: compass bearing, straight-line distance, and elevation above the horizon. The scope can run north-up or heading-up; the card's numbers are the same either way, and the distance shown is the ground distance to that aircraft.

With VoiceOver running, the same line is spoken in ATC phraseology, bearings digit by digit: "Traffic bearing one one two, twelve miles, seventy-eight degrees high."

Routes

Naming the flight, not just the airframe

ADS-B gives identity (a hex code, usually a callsign) but not where a flight is going. Overflight resolves routes server-side, keyed on the aircraft's unique hex code through AeroDataBox — callsign-keyed lookups return stale schedule data too often near a hub, so adsbdb serves only as a fallback — and checks the result's geometry against where the aircraft actually is before showing it. A route that doesn't pass near the aircraft's position is treated as unknown rather than displayed wrong. Some owners ask the FAA to keep their routes private (the LADD program); Overflight honors that and shows “Route Withheld” instead. Lookups are cached, so the network sees each flight once, not once per user-poll.

Incoming

What it takes to turn the screen amber

Notable traffic, military and otherwise unusual airframes, is scored separately. The amber INBOUND takeover doesn't fire because something interesting is merely nearby. The aircraft has to be closing on your position across several consecutive position reports, on a steady track, with implausible position jumps filtered out. Then the carousel pauses and a countdown runs to overhead. Familiar visitors decay: an airframe that shows up day after day gradually loses its claim on the screen.

Scope

A flight tracker for one question

Overflight is a flight tracker in the narrowest sense: one question, asked from one spot. What is that, and where do I look? There's no world map, flight history, or airport boards. If you want the atlas instead of the instrument, that's a different product, and a good one; see the Overflight vs Flightradar24 comparison.