Two aircraft. Same vertical slice of airspace. A 100-knot speed differential between them. The geometry was always the problem — the regulation just hadn't caught up. **The January 2025 collision near Reagan National exposed a structural gap in how US airspace was governed, not merely how it was flown.** A CRJ-700 on final approach and a US Army UH-60 Black Hawk on a training flight occupied the same constrained corridor above the Potomac River. Both were operating legally. Neither was where the rules said they couldn't be. Radar separation isn't a proximity alarm. It's a guaranteed minimum buffer — enforced by controllers, not pilots — that ensures aircraft never share the same geometric space within defined parameters. **That guarantee historically applied to IFR fixed-wing traffic.** Helicopters operating VFR near major airports were largely governed by see-and-avoid: the principle that pilots visually acquire conflicting traffic and maneuver accordingly. **See-and-avoid assumes reaction time. Closure rates above 200 knots don't offer it.** Helicopters earned their carve-out from separation rules for legitimate reasons. They operate at lower speeds, variable altitudes, and with maneuvering flexibility that makes them genuinely different from jets. Integrating them into rigid IFR separation frameworks wasn't practical. So they existed in the gaps — legally, routinely, and without guaranteed buffers from the fast-movers sharing their airspace. Reagan National compounds every variable. Over 300 daily operations funnel through one of the most laterally constrained approach corridors in US aviation. The Potomac valley limits options. Altitude windows compress. The margin for geometric conflict was always thin. The FAA's new radar separation mandate for helicopters in congested airspace doesn't rewrite the physics. **It acknowledges, formally, that the previous framework required humans to solve a geometry problem faster than humans can solve it.** The airspace was legal. The closure rate was not survivable. Those two facts coexisted for years before Washington made them impossible to ignore.