see-and-avoid at two hundred knots

Problem statement

The U.S. air traffic control system relies heavily on the "see-and-avoid" concept and visual separation in terminal airspace — despite known human perceptual limitations that make visual detection of conflicting traffic unreliable at high closure rates, in low visibility, and in congested airspace. ADS-B Out (transponder broadcast) has been mandated since 2020, but ADS-B In (the cockpit display component that lets pilots see nearby traffic) has not been required despite NTSB recommendations dating to 2008. The January 2025 Reagan National midair collision — killing 67 — validated these failures with catastrophic consequence.

Why this matters

The DCA midair killed 67 people — the deadliest U.S. aviation disaster in over two decades. NTSB investigators documented 15,214 close-proximity events between commercial airplanes and helicopters at DCA (within one nautical mile laterally and 400 feet vertically) from October 2021 through December 2024 — a period spanning 944,179 commercial operations — indicating enormous pre-existing risk. Visual separation is used routinely at hundreds of airports nationwide, and terminal airspace operations affect every commercial airport in the country.

What’s been tried and why it hasn’t worked

TCAS (Traffic Collision Avoidance System) provides resolution advisories for equipped aircraft but is designed for en-route encounters, not terminal-area operations at low altitude. ADS-B Out broadcasts aircraft position, but the complementary ADS-B In — which would display nearby traffic on cockpit displays — remains unmandated nearly two decades after the NTSB first recommended it in 2008. In the DCA collision, the Black Hawk was equipped with ADS-B Out but the NTSB reported it was not transmitting on the accident flight — and the airliner carried no ADS-B In display on which its crew could have seen the helicopter. Air traffic control relies on radar and controller judgment to separate traffic, supplemented by visual separation during VFR conditions. The DCA investigation found that the air traffic system relied heavily on visual separation to keep traffic flowing, without adequately accounting for the limitations of the see-and-avoid concept. No automated conflict detection system exists specifically for helicopter/fixed-wing interactions in terminal airspace. The NTSB issued 50 safety recommendations from this single investigation — 33 of them directed to the FAA and eight to the U.S. Army.

What would unlock progress

An ADS-B In mandate would give pilots direct awareness of nearby traffic — a fundamental capability gap today. Automated conflict detection algorithms designed specifically for terminal airspace (with mixed helicopter and fixed-wing traffic at low altitude and high closure rates) could supplement controller judgment. Systematic analysis of near-miss data — 15,214 close-proximity events were logged at DCA from October 2021 through December 2024, yet the risk was not acted on — could drive proactive airspace redesign rather than waiting for the next catastrophe.

Entry points for student teams

A team could prototype a terminal airspace conflict detection algorithm using publicly available ADS-B data (e.g., from OpenSky Network or ADS-B Exchange) to model helicopter/fixed-wing encounter geometries near busy airports. Another approach: design a near-miss trend analysis pipeline that ingests FAA ASRS or mandatory occurrence data and surfaces emerging collision-risk hotspots. Skills in geospatial data analysis, signal processing, or human factors would be most relevant.