Two aircraft on the same instrument approach to a mountain aerodrome in heavy fog. The cloud base sits below the surrounding ridge tops; the runway is invisible until short final.

Aircraft A carries a TerraNexus DGGS reference. The published approach is encoded as an indexed zoneSet the aircraft tests against continuously — a primary navigation reference, not a fallback. The reference is certified, immutable, and unspoofable: membership is integer arithmetic against published structure, with no external signal to deny, jam or distort.

Aircraft B flies the conventional architecture. GNSS feeds the INS, which dead-reckons forward; modern INS drift is 0.6–2 nm/hour. When GNSS is degraded — by multipath off ridge walls, by jamming, or by spoofing — the INS has no external check. In a 3,000 m valley, 1 nm of lateral drift is fatal.

Press PLAY. Watch B's believed versus actual position. The pilot of B has no way to detect the drift; the pilot of A has continuous directional guidance independent of GNSS, weather and visibility.