The question
What plane is that flying over my house?
The position data is public and free to query. Here is the API, and what it costs to turn it into an answer.
Why this is awkward
The question feels like it should have a one-tap answer, and nearly does: the big flight trackers will tell you, and their free tiers genuinely work. What they also carry is advertising, and the parts people find most interesting — what type of aircraft it is, where it came from — tend to sit behind a subscription.
The frustrating part is that none of the underlying data belongs to anyone. Aircraft broadcast their own position continuously over ADS-B, in the clear, and volunteers with cheap receivers feed it into open networks. It is about as public as data gets.
So it is worth knowing you can ask those networks directly, for nothing.
Doing it yourself
The OpenSky Network publishes a free REST API over exactly this data. Give it a bounding box around where you are standing and it returns every aircraft currently inside it, with position, altitude, heading and callsign. No key is needed for anonymous access, though the rate limits are tighter without an account.
A box of roughly a tenth of a degree either side of you is about eleven kilometres north to south, which is a sensible patch of sky to ask about:
curl "https://opensky-network.org/api/states/all\
?lamin=51.45&lomin=-0.20\
&lamax=51.65&lomax=0.00"
# Each entry in the states array is flat:
# [0] icao24 hex address, the aircraft's id
# [1] callsign e.g. "BAW117 "
# [5] longitude
# [6] latitude
# [7] baro_altitude metres
# [10] true_track degrees clockwise from northWhat that costs you
- It answers with an identity, not with an aircraft. `icao24` is a hex address and the callsign is an airline code — turning either into "an A320, going to Madrid" needs a separate registration database you have to find, download and keep current.
- It gives you a list, and you asked about the sky. Converting a latitude, longitude and altitude into "behind you, about thirty degrees up" is spherical trigonometry, and getting the bearing right relative to the way you are facing needs the compass as well.
- Anonymous requests are rate limited, and the limits are low enough that anything polling regularly will hit them.
- Coverage is volunteer-fed, so it is excellent over cities and patchy over countryside and water — and the API does not distinguish "nothing there" from "nobody is listening there", which are very different answers.
- There is no glanceable version. A curl in a terminal is not what you want while standing in the garden pointing at something.
Or the app that does it
Plain and Simple Planes asks the same volunteer networks and does the arithmetic you would otherwise be writing. It sorts by what is nearly overhead, and tells you which way to look and how far up.
There are three ways of seeing the same sky, and a real map only if you want one. Filters say what they are hiding rather than quietly dropping things, and where a flight is going is shown when that answer is honest and labelled as half an answer when it is only half. The reference data ships with the app, and the widget admits it is not live.
What leaves your phone is a coordinate rounded to about a kilometre, and nothing else. No account, no name, no device or advertising identifier, no analytics, no tracking, and nothing to buy. It goes straight to the volunteer network that answers the question, not through any server of mine — there isn't one. Nobody stores it, including me.