reference· 2 min read

OpenAir airspace format

The OpenAir airspace format we-fly reads and writes — records, coordinate and altitude grammar, dialect compatibility, and an interactive spec you can test in the browser.

What this is

OpenAir is the plain-text, line-oriented format for describing airspace as points, circles and arcs. we-fly reads OpenAir in a few places — the post-flight airspace check accepts a user-supplied OpenAir file to supplement the built-in openAIP data, and the XC planner renders airspace overlays. If you produce or consume airspace files for we-fly, this is the reference.

Interactive specification

We maintain a self-contained, interactive spec you can read and test right in the browser:

→ OpenAir format — interactive specification

It includes a live line inspector (paste OpenAir, see every record decoded), a filterable record explorer, and a coordinate converter — no upload, nothing leaves the page.

The format in one screen

Line-oriented. One record per line: a 1–2 letter prefix, a space, then arguments. An airspace block starts at an AC record and runs until the next AC or end of file.
Coordinates are latitude longitude with hemisphere letters, WGS84 — both DMS (53:47:06N 008:21:41E) and decimal-minute (39:36.8N 119:46.1W) notations.
Altitudes are in feet: FL145, 1000ft AMSL, GND, UNL.
Geometry: DP polygon points, DC circle, DA/DB arcs around a V X= centre.

Group	Records
Metadata	`AC` class · `AN` name · `AH` ceiling · `AL` floor · `AT` label
Extended (v2.1)	`AY` type · `AF` frequency · `AG` station · `AI` id · `AA` activation · `AX` transponder
Geometry	`DP` · `DC` · `DA` · `DB` · `DY`
Variables	`V X=` centre · `V D=` direction · `V W=` width

Dialects & compatibility

Two dialects coexist: v1 (original / Winpilot) and v2 / v2.1 (extended / Naviter — the maintained standard). v2.1 is additive over v1: a well-behaved v1 reader parses a v2.1 file's geometry and core fields and skips records it doesn't recognise. The one catch — the extended dialect can move the airspace type from AC to AY, so a v1-only reader that ignores AY loses that classification. Keep AC self-sufficient when you need broad compatibility.

Sources

The interactive spec reconciles the Naviter / SeeYou spec, the openAIP OpenAIR parser (our reference implementation), and the original Winpilot definition.