A controller can flag nearby traffic, a pilot can scan the sky, an onboard receiver can display another aircraft’s position and a collision avoidance system can recommend an evasive maneuver. While each action contributes to the same objective, none guarantees safety alone. As drones, helicopters, commercial aircraft and emerging air taxis share more airspace, the challenge extends beyond detecting traffic. Aircraft need protection that accounts for their performance, operating environment and mission. For Tom Furey, CEO of Sagetech Avionics, the answer centers on layers. On a recent Dawn of Autonomy podcast, he provided a tutorial on how those technologies fit together, where existing protections fall short and how Sagetech approaches the gaps.
Aviation Safety Starts With Controllers and Flight Crews
Furey brings a personal understanding of aviation risk. As a Naval Flight Officer aboard the A-6 Intruder, including during the first Gulf War, he relied on identification technology to help protect against friendly fire. That experience connects directly to Sagetech’s work in transponders, military identification friend-or-foe (IFF) systems and collision avoidance.
In civilian airspace, controllers help separate traffic, while pilots retain responsibility for seeing and avoiding other aircraft when conditions permit. Those protections complement each other, but visibility, workload, communications problems and unexpected traffic can weaken them.
“Each of those layers could prevent a collision,” Furey said. But a pilot cannot see through terrain or clouds, and a controller may not provide a warning about every aircraft that presents a threat. That creates a role for onboard surveillance and, ultimately, systems that help crews decide what to do.
ADS-B Makes Aircraft Visible, but Visibility Is Not Avoidance
Furey uses Marco Polo, a familiar childhood game, to explain conventional transponders. An interrogator sends a signal, and an aircraft’s transponder replies with information about that aircraft.
Automatic Dependent Surveillance-Broadcast, or ADS-B, changes the exchange. Instead of waiting for an interrogation, an aircraft broadcasts information about itself. Furey compares that persistent announcement to the refrain from Horton Hears a Who: “We are here, we are here, we are here.”
The distinction between ADS-B Out and ADS-B In matters. Out broadcasts information. In receives information that can support an onboard traffic picture. Sagetech incorporates ADS-B receivers into its MX transponder series, Furey explained.
Yet a traffic display still leaves someone responsible for interpreting the picture. Collision avoidance goes further. As Furey put it, the system “not only presents to the pilot, or in the case of a drone, the operator on the ground, a picture of the traffic around them,” but also “tells them what to do about it.” That additional layer helps reduce the mental work of assessing a developing encounter while managing the aircraft.
ACAS X vs. TCAS: From Traffic Alerts to Tailored Guidance
The Traffic Alert and Collision Avoidance System, or TCAS, established an important safety foundation. TCAS I provides traffic advisories. TCAS II adds resolution advisories that direct vertical responses to collision threats. Compatible systems can coordinate those responses so two aircraft do not choose conflicting maneuvers.
The newer Airborne Collision Avoidance System X family, commonly called ACAS X, extends that approach across different aircraft and operations. It consists of an entire family of systems that recognize that a helicopter, airliner and small drone cannot necessarily respond to a threat in the same way:
- ACAS Xa addresses conventional transport aircraft.
- ACAS Xo supports specific operations involving intentional proximity, including closely spaced parallel approaches.
- ACAS Xr addresses rotorcraft and vertical takeoff and landing aircraft.
- ACAS Xu and ACAS sXu address different unmanned aircraft applications.
Furey described ACAS X as predictive, using aircraft tracking information and probabilistic models to assess how an encounter may develop. He emphasized that probabilistic reasoning does not mean unpredictable onboard behavior. “If the same exact situation happens twice, the same exact response will be called for,” he said.
Guidance also depends on the variant. Furey highlighted horizontal and blended maneuver options in applicable ACAS X implementations, such as “descend, left.” These expand the available responses beyond the vertical guidance associated with TCAS II.
Hybrid Surveillance Helps Manage Crowded Radio Spectrum
More aircraft do not simply create more traffic conflicts. They also place demands on the radio frequencies that support surveillance. Furey explained that conventional transponder interrogations and replies use 1030 MHz and 1090 MHz. Repeated interrogations in busy airspace add communications traffic precisely where reliable surveillance matters most.
Hybrid surveillance combines ADS-B information with active surveillance. Rather than continually interrogating every aircraft, a system can use received broadcasts and selectively interrogate aircraft to validate tracks.
That validation serves an important purpose. Receiving a claimed ADS-B position does not, by itself, prove that an aircraft occupies that location. Furey described using radio-signal timing to help confirm the presence of the transmitting aircraft. The approach can reduce interrogation demand while maintaining surveillance integrity.
For Sagetech, integration also matters. Furey described a combined interrogator-transponder architecture that brings surveillance functions and collision avoidance capabilities together in a compact package.
Low-Altitude Collision Avoidance and the DCA Lesson
Low-altitude flight exposes a difficult boundary for collision protection. Aircraft operate close to terrain, structures and other traffic, while avoidance systems must avoid issuing inappropriate guidance.
Furey connected that challenge to the January 29, 2025, collision between a regional airliner and an Army Black Hawk near Ronald Reagan Washington National Airport. The accident underscores the importance of distinguishing a traffic warning from an actionable resolution advisory.
The NTSB’s airplane-systems presentation states that the airliner’s crew received a TCAS traffic advisory about 20 seconds before impact. TCAS did not generate a resolution advisory at that altitude. The system had switched off during the landing sequence, and the helicopter’s lack of ADS-B Out made it invisible.
Furey discussed simulations exploring how rotorcraft collision avoidance could change such an encounter. He presented those results as evidence of potential protection, not proof that a particular installation would have prevented the accident.
Simulations Show the Potential of Rotorcraft Collision Avoidance
Specifically, Furey pointed to simulation work he attributed to MIT that examined how different avionics configurations might have changed the DCA encounter. According to his account, researchers modeled the aircraft and flight profiles across 15 equipment scenarios, comparing combinations of TCAS, ADS-B and rotorcraft collision avoidance.
Thirteen scenarios did not include ACAS aboard the helicopter. Furey said seven of those produced near-midair collisions, while he characterized all 13 as too close for comfort. The two scenarios that included ACAS aboard the helicopter produced substantially greater separation, with horizontal miss distances of approximately 1,800 and 2,300 feet. Those figures describe the simulated aircraft’s horizontal separation, not their vertical clearance.
The important distinction involved receiving, not just broadcasting. Even without transmitting its own ADS-B position, the helicopter could have received the airliner’s ADS-B broadcasts and used that information to generate resolution advisories, Furey explained. In those modeled encounters, onboard collision avoidance supplied something beyond a traffic picture: guidance on how to respond.
For a helicopter crew navigating at low altitude through a busy urban environment, that additional help could matter. Furey described pilots managing terrain clearance, visual navigation and surrounding lights while trying to identify other traffic. An audible warning paired with a clear maneuver recommendation could help crews recognize and respond to a threat amid those competing demands.
Still, Furey stopped short of claiming that the technology would have prevented the actual accident. He presented the simulations as evidence of potential protection, not a guarantee of a real-world outcome. “Nobody can say whether it would have or not,” he said, “but it certainly adds a very, very important layer of safety.”
Reducing nuisance alerts also matters. Repeated warnings that crews perceive as unnecessary can erode attention and trust. Furey said improved surveillance and threat prediction help ACAS reduce those alerts, particularly around terminal areas.
Vehicle-to-Vehicle Communication for Firefighting and Formation Flight
Some missions require aircraft to remain close together. Firefighting, formation flying and aerial refueling create a different problem from an unexpected encounter between unrelated aircraft. “ACAS can’t do everything,” Furey explained.
Sagetech and Israeli partner Ciconia are developing a coordination and collision avoidance system, or C&CAS, to address intentional close-proximity operations. Furey described support through a BIRD Foundation homeland security grant and demonstrations involving firefighting and military users.
The approach combines Sagetech’s hardware and surveillance expertise with Ciconia’s coordination logic. A dedicated vehicle-to-vehicle link exchanges information among participating aircraft with lower latency than the ADS-B-based exchange Furey described. That faster exchange becomes especially important when aircraft operate close together.
The system distinguishes normal coordinated flight from a developing hazard. Furey said its alerting approach can direct an uncrewed aircraft’s autopilot to move away before escalating to broader separation guidance. ADS-B remains relevant for detecting outside traffic that does not participate in the local network.
Standards Turn Collision Avoidance Technology Into Deployable Safety
Technical capability alone does not deliver operational protection. Developers also need performance standards, certification and suitable communications infrastructure.
Furey expects ACAS Xr minimum operational performance standards to complete review near year-end. He described those standards as a basis for certification, not as certification itself, and identified additional Sagetech integration and certification work ahead.
Dedicated spectrum for vehicle-to-vehicle communications remains another challenge. Furey described ongoing work with partners and standards committees, while treating future protected spectrum as an objective rather than an established outcome.
Those dependencies reinforce the central lesson: safer autonomy requires connected protections, not a single replacement for pilots, controllers or existing surveillance.
Safer Skies Depend on Layers That Work Together
For Furey, a former aviator himself, the goal is not to make pilots or controllers less essential. It is to give them another chance to catch a threat before an encounter becomes an accident. For Sagetech, that means matching the protection to the mission, from collision avoidance in shared airspace to tighter coordination over a wildfire. “We believe in all of those layers,” Furey said.
As more aircraft share the sky, the measure of progress will not be how much technology they carry, but how well those layers work together when crews need them most.