Practical guide
How to analyze an XC flight from an IGC file
The IGC file your vario saves at the end of the day is not just a track to file away: it is the full record of the flight. Here is what it contains and how to read it after a cross-country.
What an IGC file contains
An IGC is a text file standardized by the FAI. The part that matters is the B-records: one per GPS fix, typically every 1 to 2 seconds.
Each B-record carries five key pieces of data: UTC time of the fix, latitude, longitude, barometric altitude (from the pressure sensor) and GNSS altitude (from GPS). Barometric altitude is the one that matters for the vertical, because it is continuous and free of GPS noise.
- Time: typical 1-2 s cadence, dense enough to reconstruct every turn in a thermal.
- Lat / Lon: the ground track, from which distance and glides are computed.
- Barometric altitude: the basis for vario, gains and climb rate.
- Header (H records): pilot, wing, date, time zone and instrument type.
The six things to read after an XC flight
A distance flight is not judged by kilometres alone. After every XC it pays to look at six numbers, because they tell you where you gained and where you lost time.
- Distance and route: free distance or triangle, and how far your line deviated from optimal.
- Glides (glide ratio): the ratio between distance covered and altitude lost on transitions. This is the metric that rewards clean lines.
- Climbs (climb rate): the average climb rate in each thermal, in m/s. Badly centred thermals show up immediately here.
- Altitude: maximum altitude, average cloud base and total gain summed over the climbs.
- Time climbing vs gliding: the share of the flight spent climbing tells you how efficient your moving was.
- Weak points: the stretches where you lost altitude without advancing, usually transitions started too low.
How RSFly reads your IGC
RSFly takes the raw B-records and derives the 3D replay on real terrain, automatic thermal detection and performance metrics, without you ever opening a spreadsheet.
The replay colours the track by altitude and shows thermal columns where the climb rate was highest, so you can read at a glance where the flight worked and where it did not.
In short
- The value of an IGC is in the B-records: time, position and barometric altitude, every 1-2 seconds.
- After an XC look at distance, glides, climbs, altitude, time in thermals and the weak stretches.
- Barometric altitude, not GPS altitude, is the basis for reading the vertical.