The resurgence of mid-air collision fatalities in a compressed three-week window has reignited long-standing debate within the aviation community about the structural limitations of see-and-avoid as a primary collision avoidance strategy. The incidents highlighted in this discussion share a critical common denominator: neither aircraft involved was equipped with ADS-B Out, the FAA-mandated technology that broadcasts GPS-derived position data to both ground infrastructure and other equipped aircraft. While the FAA's January 2020 ADS-B Out mandate applies to operations in Class A, B, and C airspace, as well as Class E airspace above 10,000 feet MSL and within 30 nautical miles of Class B primary airports, vast swaths of uncontrolled and lower-altitude airspace remain entirely outside that requirement — and it is precisely in those environments where light aircraft, training operations, and recreational flying are most concentrated.
The author's observation about the gap between FlightRadar24's traffic picture and actual airspace occupancy reflects a systemic surveillance blind spot that professionals building traffic awareness tools encounter immediately. Mode S transponders, which are far more common in the legacy fleet than ADS-B Out units, provide a secondary surveillance radar return and an ICAO 24-bit address, but they do not autonomously broadcast GPS position. Their tracking depends entirely on ground radar interrogation, meaning aircraft operating outside radar coverage — in mountainous terrain, low altitudes, or remote airspace — are effectively invisible to other pilots using electronic situational awareness tools. Multilateration (MLAT), used by aggregators like FlightRadar24, can approximate position by triangulating Mode S replies across a network of receiver stations, but its accuracy degrades with sparse receiver density and is architecturally dependent on ground infrastructure that has no mandate for universal coverage.
FLARM, a system widely adopted among European glider and light aircraft communities, presents its own interoperability problem. It uses a proprietary RF protocol that requires both aircraft to be FLARM-equipped to exchange traffic data, creating a closed ecosystem that offers no protection against the broader non-equipped fleet. ADS-L — a low-power, lightweight position broadcasting standard being advanced through EASA and international standardization bodies as a practical solution for ultralight, glider, and experimentally certificated aircraft — remains in early deployment stages and lacks the regulatory framework and equipage rates necessary to meaningfully reduce collision risk in the near term. For working pilots, this means the electronic traffic picture in Class G and lower Class E airspace is fundamentally incomplete regardless of avionics sophistication.
The operational implications for professional pilots extend beyond personal situational awareness. Part 91 operators flying reciprocating or turboprop aircraft below 18,000 feet in uncontrolled airspace routinely encounter traffic not depicted on ADS-B In displays, TCAS, or any onboard system. Flight training environments, skydiving operations, agricultural aircraft, and experimental builders represent large segments of the active fleet with no realistic near-term path to full ADS-B Out equipage. Helicopter EMS crews, pipeline patrol operators, and low-altitude survey pilots face this exposure on every flight. The absence of a universal surveillance mandate below certain altitude thresholds is not an oversight but a deliberate policy accommodation for aircraft categories where the cost and weight burden of certified ADS-B Out systems was deemed prohibitive — a tradeoff that continues to carry lethal consequences.
The broader trend reveals a collision avoidance ecosystem that is fragmented by design and deteriorating by attrition. The FAA's ADS-B mandate was intended to modernize the National Airspace System's surveillance backbone, but its carve-outs preserved legacy exposure in exactly the altitudes and airspace classes where collision geometry is most dangerous — low-speed, high-density, visually demanding environments with minimal separation assurance. Meaningful progress will require either a mandate extension to lower-altitude operations with affordable compliance pathways, accelerated deployment of ADS-L or equivalent low-power alternatives, or both. Until either occurs, see-and-avoid remains the last — and often only — layer of protection for millions of flight hours annually, operating in airspace that current surveillance architecture cannot reliably characterize.