What is an IGC file and how do you open it?

The .igc file your flight instrument or phone app records is the single official record of your flight. It is what goes to XContest, to a competition, to the club league — and what Variograph analyses.

What is IGC?

A plain-text flight-log format defined by the FAI (World Air Sports Federation). Open it in a text editor and it reads line by line. The first letter of each line is the record type:

• A — manufacturer and serial number of the logger
• H — headers: date, pilot name, glider, GPS/pressure sensor
• B — position fix: time (UTC), latitude, longitude, validity, barometric altitude, GPS altitude
• G — the file's digital signature (proof it was not tampered with)

At one fix per second, an hour of flying is about 3,600 B lines. The whole analysis comes out of them.

Why two altitudes?

A B-record carries barometric (pressure sensor) and GPS altitude. They fail differently — barometric drifts with QNH, GPS vertical error jumps. Competitions and records usually reference barometric; GPS-only logs (some phone apps) are flagged as such. Variograph's data-quality report shows separately whether a pressure channel exists.

Where do I get one?

• XCTrack: flight list → flight → share/export → IGC
• Flymaster / Skytraxx / Naviter: connect over USB and copy from the IGC folder, or download with the maker's app
• FlySkyHy and other iOS apps: flight → share → IGC
• XContest: "download IGC" on your own flight page

How do I open it?

A text editor reads it but gives it no meaning. For analysis, upload it to a flight-analysis tool. In Variograph, drag and drop on the home page; when signed in, the flight is saved to your dashboard with thermals, glides, net vario, the wind profile and 3D replay ready.

IGC vs GPX

GPX is a general-purpose GPS track format — running watches produce it too. It has no barometric altitude, device identity or signature, so it is not accepted for competitions and leagues, and some metrics stay empty in analysis. Variograph accepts both; prefer IGC for full analysis.

What is the signature for?

The G-record proves the file was not modified after recording. Editing the header by hand (the pilot name, say) breaks it. Variograph shows signature status in four classes; details: IGC signature and G-record verification.