Invisible Aircraft in U.S. Airspace: Regulatory Gaps and Mid-Air Collision Risk for Part 121 Operators

Scheduled air carrier aircraft operate at large and small commercial airports across the U.S. National Airspace System. These turbine-powered aircraft fly at high speeds during departure and approach, yet many commercial airports are not covered by regulations requiring general aviation aircraft to transmit their positions, and some remain exempt from existing requirements. This regulatory gap forces airline pilots to rely on see-and-avoid methods that are impractical at turbine aircraft speeds. This study conducts a quantitative exploratory analysis of three data sources, using a PRISMA-style flow diagram, to examine the frequency of near mid-air collisions involving airline and general aviation aircraft and to identify high-risk airspace. The analysis highlights 212 small and non-hub airports with significant enplanements where the risk to commercial flight safety is most pronounced. These findings highlight a critical oversight in airspace regulation and demonstrate the need for targeted research, enhanced pilot training, and policy improvements to mitigate collision hazards.