The Federal Aviation Administration’s (FAA) placement of a helicopter route in close proximity to a runway approach path; their failure to regularly review and evaluate helicopter routes and available data, and their failure to act on recommendations to mitigate the risk of a midair collision near Ronald Reagan Washington National Airport (DCA); as well as the air traffic system’s overreliance on visual separation in order to promote efficient traffic flow without consideration for the limitations of the see-and-avoid concept. Also causal was the lack of effective pilot-applied visual separation by the helicopter crew, which resulted in a midair collision. Additional causal factors were the tower team’s loss of situation awareness and degraded performance due to the high workload of the combined helicopter and local control positions and the absence of a risk assessment process to identify and mitigate real-time operational risk factors, which resulted in misprioritization of duties, inadequate traffic advisories, and the lack of safety alerts to both flight crews. Also causal was the Army’s failure to ensure pilots were aware of the effects of error tolerances on barometric altimeters in their helicopters, which resulted in the crew flying above the maximum published helicopter route altitude. Contributing factors include: · the limitations of the traffic awareness and collision alerting systems on both aircraft, which precluded effective alerting of the impending collision to the flight crews; · an unsustainable airport arrival rate, increasing traffic volume with a changing fleet mix, and airline scheduling practices at DCA, which regularly strained the DCA air traffic control tower workforce and degraded safety over time; · the Army’s lack of a fully implemented safety management system, which should have identified and addressed hazards associated with altitude exceedances on the Washington, DC, helicopter routes; · the FAA’s failure across multiple organizations to implement previous NTSB recommendations, including Automatic Dependent Surveillance–Broadcast In, and to follow and fully integrate its established safety management system, which should have led to several organizational and operational changes based on previously identified risks that were known to management; and · the absence of effective data sharing and analysis among the FAA, aircraft operators, and other relevant organizations.