My Validation Layer Was Correctly Deleting 16% of My Good Data

Originally published at ai.bedvibe.studio . I built a real-time tracker in Rust — about two thousand lines — that reads a live ADS-B feed, keeps a Kalman-filtered track per aircraft, and screens every pair for closest approach against separation minima. Roughly 150 aircraft, a full cycle in under a millisecond. It ran clean. Tests passed, the picture looked right, the numbers were plausible. It was refusing about one measurement in nine , and the only reason I ever found out is that the rejections went to a counter instead of a log line. The gate has a sub-second tolerance for clock error The tracker runs an innovation gate: when a position arrives, the filter predicts where the aircraft should be, and if the measurement is too far from that prediction it is rejected as physically impossible rather than believed. Once a track converges the innovation standard deviation settles around 36 m, so a five-sigma gate sits at roughly 180 m. An airliner at 250 m/s covers 180 m in 0.7 seconds . So the gate's entire tolerance for a wrong timestamp is under one second. Any pipeline that mis-times its measurements by more than that will have them rejected — correctly, and invisibly. The feed reports its own staleness. The pipeline dropped it. Every ADS-B record carries a field saying how old that position already was when the response was generated. In the original build it was parsed into the contact struct and never read again — the only other place that field appeared in the entire codebase was as 0.0 in test fixtures. Every measurement was therefore stamped with the tracker's own cycle clock, as though it had been observed at the instant it landed. This is the common case, not an exotic one. A field that is decoded and then unused looks identical to a field that is decoded and used , right up until you go looking for its second reference. Here is what that field actually contains, sampled across two consecutive polls of the live feed: reported age of position median 0.31 s p