TCAS Archives - Leeham News and Analysis

Leeham News and Analysis has accumulated a substantial body of work under its TCAS archive, spanning a decade of coverage that traces the evolution of airborne collision avoidance from foundational transponder technology through ADS-B integration and into the emerging complexity of eVTOL traffic management. The archive's oldest entry, Bjorn Fehrm's 2016 examination of transponders as "the kingpin of safe air navigation," established the conceptual baseline: the entire architecture of aircraft separation, from Mode C altitude encoding to TCAS resolution advisories, depends on the integrity and ubiquity of transponder infrastructure. That framing has proven durable as subsequent entries built upon it through 2018's two-part treatment of ADS-B's role in augmenting TCAS, explaining how the 978 MHz UAT channel in the United States expanded bandwidth for traffic services and how ADS-B Out broadcasts fundamentally change the quality of surveillance data available to both ground systems and other aircraft.

The 2018 navigation series is particularly instructive for instrument-rated pilots operating under Part 91 or Part 135, as it directly addressed the transition from interrogation-based surveillance — where TCAS actively queries nearby transponders and relies on reply timing for range — to the cooperative, GPS-derived position broadcasts of ADS-B. That distinction matters operationally: ADS-B-equipped aircraft provide neighboring traffic systems with precise geodetic position, track, and velocity data rather than the slant-range approximations of legacy TCAS. The result is faster threat resolution geometry and reduced nuisance RA rates in high-density terminal environments, a benefit that crews operating into KORD, KLAX, or KEWR on busy bank times have a practical stake in understanding.

The 2022 eVTOL piece surfaces the collision avoidance problem's next layer of difficulty. Outside controlled airspace — where most initial eVTOL corridors and drone operations are being conceived — the existing TCAS and ADS-B regulatory framework does not cleanly apply. Rulemaking on how these aircraft avoid one another, manned aircraft, and unmanned systems remained unsettled as of that writing, and the FAA's Urban Air Mobility and BVLOS drone rules have continued to develop incrementally since. For corporate flight departments operating turbine aircraft into vertiport-adjacent airports or secondary fields that may host eVTOL operations, the absence of a finalized separation standard represents a genuine operational risk management gap, one that chief pilots and dispatch should be tracking alongside airspace NOTAM activity.

The most recent entry in the archive — Vincent Bianco's June 2026 "Part 4: The Pattern That Compounds" — introduces a more systemic and critical lens. The framing of "a generational institution responding to its own documented failures with technology" suggests an examination of whether the commercial aviation manufacturing sector, likely Boeing in the post-MAX and 737-900 quality-control context, has defaulted to technical solutions where cultural and procedural accountability would be more appropriate. That argument, if sustained across Bianco's series, carries weight for operators who rely on manufacturer service documentation and airworthiness directives as their primary safety signal: if the underlying failure patterns are being papered over by avionics overlays rather than corrected at the process level, the collision avoidance or surveillance system sitting in the nose of a new delivery may be solving for the wrong problem.

Taken together, the Leeham TCAS archive illustrates a trajectory that professional flight crews and aviation safety professionals should recognize: collision avoidance has migrated from a self-contained radio frequency problem to an ecosystem-level challenge involving GPS integrity, uncrewed vehicle proliferation, airspace architecture, and now manufacturing culture. Pilots flying TCAS II Version 7.1-equipped aircraft today benefit from decades of iterative improvement, but the next decade's airspace — denser, more heterogeneous, and populated by aircraft types TCAS was never designed to interrogate — will demand fluency with the policy debates these archives document, not just the cockpit procedures they ultimately produce.