Thermals
Thermals in an IGC file: how to spot them after the flight
September 09, 2026
To look for a thermal in an IGC file, examine sustained altitude gain alongside the track shape. Circles and drift are clues to interpret: the track records the pilot’s movement, not the air mass directly.
What footprint does a thermal leave in the trace?
To look for a thermal in an IGC file, examine sustained altitude gain alongside the track shape. Circles and drift are clues to interpret: the track records the pilot’s movement, not the air mass directly.
How does RSFly.app highlight them?
RSFly estimates climbing segments from flight data and displays gains and rates in the views available for the plan. Noise, gaps and recording interval can affect detection.
On the thermal map, climbs from flights shared by the community become a browsable layer: not a forecast, but the collective memory of where the air has already worked.
Does yesterday’s thermal count tomorrow too?
No — and whoever promises otherwise is selling smoke. A spot that worked yesterday is statistical information, not a forecast: conditions, season, wind and time of day change everything.
Use post-flight analysis to understand your own climbing behaviour and to learn which slopes work most often; the decision in the air remains yours, with the usual safety rules.
Apply it to your flight
Free includes the logbook, essential statistics and Standard 2.5D Replay. Plus adds cinematic 3D Replay, detailed analysis, comparisons and exports. The Plans page describes current availability and terms.
- Open the IGC file in the logbook and check its date, duration and track continuity.
- Choose a climb or transition and compare time, altitude and replay over the same interval.
- Record observations and compare flights in similar conditions, keeping data separate from interpretation.
In short
- To look for a thermal in an IGC file, examine sustained altitude gain alongside the track shape. Circles and drift are clues to interpret: the track records the pilot’s movement, not the air mass directly.
- RSFly estimates climbing segments from flight data and displays gains and rates in the views available for the plan. Noise, gaps and recording interval can affect detection.
- Past thermals are useful statistics, never a forecast: the decision in the air belongs to the pilot.