On the tower display, every aircraft had a tag. A callsign, an altitude readout, a tracked position. Every aircraft except one. That gap — between what the radar could see and what the safety system could act on — sits at the centre of the NTSB's findings from LaGuardia. The surface warning system didn't fail because something broke. It failed because of a design boundary that has always been there. **ASDE-X is a correlation engine, not a radar.** The system fuses two distinct data streams: raw radar skin-paint returns, which bounce off any metal object on the surface, and transponder data — Mode C, Mode S, ADS-B — which provides identity, callsign, and verified position. The conflict-alert logic runs on the correlated output. When an aircraft's transponder isn't actively transmitting, the radar may still paint a return, but the alert algorithms have nothing to correlate it against. No transponder signal means no identity. No identity means no conflict warning. The NTSB confirmed this directly: at least one aircraft involved in the collision sequence lacked an active transponder signal at the critical moment. The system saw a blip. It could not generate an alert. This distinction matters beyond LaGuardia. **Every surface safety system built on transponder-correlated logic carries the same structural blind spot.** Skin-paint radar has existed for decades. The decision to gate conflict alerts behind transponder correlation was deliberate — it reduces false alarms and provides actionable data. The trade-off is that the system's protection ends precisely where transponder reliability ends. The NTSB listed the alert failure as one of several contributing factors. That framing is careful and accurate. But the architecture question it surfaces is not specific to one airport or one incident. The radar saw the aircraft. The safety system, by design, did not.