A text file with a reputation.
Open an IGC file and it almost explains itself. H-records at the top name the pilot, the glider and the recorder. C-records hold the declared task. Then thousands of B-records — one per fix, typically every second — each a single line: time, latitude, longitude, a validity flag, and two altitudes. At the bottom, a block of seeming gibberish called the G-record. The gibberish is the whole legal system.
The format was standardized by the IGC — the International Gliding Commission of the FAI — in the 1990s, precisely so that a badge flown in Slovenia, an online-contest flight from Australia and a world record from Texas could all be read, checked and trusted by the same software forever. Plain text was not a limitation. It was the point: a format with no owner and no expiry date.
The signature that turns data into evidence.
When the flight ends, the recorder computes a cryptographic digest of everything it has written and signs it with a private key that never leaves the sealed device. That signature becomes the G-record. Validation software recomputes the digest from the file and checks it against the signature: edit a single fix — round an altitude up, trim an inconvenient engine run, splice two flights — and the check fails, loudly.
The trust chain is physical as much as mathematical. The key is protected by the recorder's sealed case and tamper detection; open the box and the device wipes its identity rather than surrender it. This is why an IGC file from an approved recorder is accepted as evidence for a world record, while the same trace from a phone app — honest as it probably is — signs nothing and proves nothing. The file is cheap to copy and impossible to quietly change, which is exactly the combination officialdom needs.
Approval has levels.
Not every logger may witness every claim. The IGC grants approval per recorder model, in tiers: the highest level is required for world and continental records; a broad middle tier covers all badges and diplomas up to and including the 1000 km diploma; and a lighter class of position recorders serves silver and gold badges and the online contests. The differences are not marketing — higher tiers demand stricter environmental testing, sealed pressure sensors and stronger tamper protection.
The practical consequence fits in one sentence: know what your recorder is approved for before the season starts, because the day you accidentally fly your diamond distance is the wrong day to read the approval documents.
The microphone that watches the engine.
A motor glider's file must prove a negative: that the engine did not run between the start and the finish. The recorder's answer is the ENL — engine noise level — a microphone inside the recorder whose sampled loudness is appended to every single B-record. An engine start is unmistakable: the value leaps from ambient double digits to near the maximum and stays there. Newer devices add MOP, a means-of-propulsion sensor wired to the powerplant itself, for aircraft whose motors are too quiet for a microphone to convict.
Evaluation software plots the noise trace alongside the barogram, and a soaring performance with a silent, flat ENL is self-evidently engine-off. It is an elegantly adversarial design: the sensor lives with the pilot, records continuously, and cannot be argued with after the fact.
Two altitudes, one verdict.
Every fix carries both a pressure altitude — logged against 1013.25 hPa, never your QNH, so that no knob setting can flatter a claim — and a GPS altitude, as the altitudes article explains in full. Convention says height claims are judged on the pressure trace, calibrated: approved recorders accept a periodic barograph calibration, a bench run through a known pressure profile that documents the sensor's error curve. GNSS altitude, once the weaker witness, is now accepted under modern rules for some claims — but the two-altitude record means every flight carries its own cross-check, forever.
Declare, fly, download.
The ritual, start to finish: put the declaration — task, turnpoints, pilot, glider — into the recorder before takeoff, because the C-record timestamp proves intent and an undeclared task can earn distance points but never a badge leg flown "by accident". Fly. Then download with software that treats the file as evidence: byte-for-byte, validated locally, original preserved. Upload the copy to the online contest, send it to the official observer, share it freely — the G-record travels inside, and anyone, anywhere, can verify it independently.
A text file, a signature, and thirty years of shared convention. It is the rare piece of aviation infrastructure that works so well nobody notices it — until the day your best flight needs a witness, and it turns out one was aboard the whole time.
The IGC-approved recorder — declaration, ENL and the signed file in a box that outlives every battery on the panel.
Standalone vario with IGC logging — one instrument, flight data and the official trace.
The system logs on the bus — with an approved recorder as the evidentiary core of the panel.