Why a properly authorised and digitally coordinated flight may still be exposed to an aircraft that never appears on the operator’s screen writes Manuel Ignacio Pérez Pan
There is a reassuring moment during the preparation of a beyond visual line of sight (BVLOS) flight when everything appears to be in place. The operational volume has been defined, the airspace has been reviewed, the required authorisations have been obtained and the relevant notifications have been issued. The planned flight may be visible within a UAS traffic management (UTM)/ U-space or flight-management environment, alongside the cooperative traffic information available to the operator.
It is easy, at that point, to feel that the airspace conflict has been managed.
Operationally, however, what has been achieved is more specific. The probability of an encounter has been reduced through planning, coordination and the exchange of available information. That is valuable, but it is not the same as having the means to detect and resolve every conflict that may still develop after take-off.
This distinction sits at the centre of the air-risk model contained in the European Union Aviation Safety Agency (EASA) EASA Easy Access Rules for Unmanned Aircraft Systems. Strategic mitigations act before the flight by reducing encounter rates or limiting the period during which the UAS is exposed to other traffic. Tactical mitigations are applied after take-off to address the residual collision risk that remains.
The terminology must be handled carefully. EASA explicitly warns that the SORA concept of “tactical mitigation” should not be confused with the formal provision of tactical separation services described in ICAO’s air traffic management framework. The title of this article is therefore not intended to suggest that every BVLOS operation requires an air traffic separation service. It draws attention to a more fundamental point: pre-flight deconfliction cannot, on its own, resolve an airborne conflict in real time.
In practical BVLOS operations, especially those conducted at very low level or along extended infrastructure corridors, the difference is far from academic. A flight may be correctly authorised and strategically coordinated while remaining exposed to an aircraft that is absent from the information available to the remote crew.
The strategic layer may have worked exactly as intended. The tactical problem can still remain.
What strategic deconfliction can achieve
Strategic deconfliction is an essential part of scalable BVLOS operations. Without the exchange of flight intent and a reliable method of identifying incompatible planned operations, it would be difficult to accommodate increasing numbers of UAS within the same low-level airspace.
Depending on the regulatory environment and the services available, the strategic layer may include flight authorisation, airspace constraints, geographical or temporal restrictions, shared flight intent, dynamic restriction information and coordination with air traffic or U-space services.
The FAA describes UTM as a collaborative ecosystem for managing low-altitude UAS operations. It can support planning, authorisation, surveillance and conflict-management functions, particularly for BVLOS operations. The FAA also describes UTM as separate from, but complementary to, air traffic services.
The distinction is even clearer in the ICAO UTM guidance. ICAO envisages civil aviation authorities and air navigation service providers making airspace constraints and flight-intent information available to UAS operators, directly or through UTM service providers. Within that concept, the UAS operator remains responsible for managing the operation safely inside those constraints without necessarily receiving positive air traffic control services from the ANSP.
This does not reduce the value of UTM. It defines where responsibility lies and prevents a digital coordination service from being credited with a level of separation assurance it may not have been designed or approved to provide.
Under the current European SORA framework, strategic mitigations can include restrictions on time, route, altitude or geographical area. They may also use common airspace structures and rules, including U-space, where the applicable conditions are met. Their purpose is to reduce the probability of an encounter or the time of exposure before the aircraft becomes airborne.
Probability reduction is not the same as conflict resolution.
A flight authorisation confirms that an intended flight satisfies the applicable conditions within a particular system and airspace. A notification makes information available to other users through the relevant channel. Flight-intent exchange can identify conflicts between operations participating in that exchange. None of these facts, by itself, establishes that every aircraft capable of entering the operational volume will be detected and managed tactically.
This is not a design failure. It is a boundary between functions.
U-space can narrow the gap, but only within defined conditions
The European U-space framework shows how the strategic and tactical layers can begin to interact more closely. Under the Easy Access Rules for U-space, activation of a UAS flight authorisation can depend on whether the planned flight conflicts with higher-priority UAS operations, e-conspicuous manned aircraft or detected non-cooperative traffic.
The same regulatory material provides for a U-space service provider to alert the operator and, where appropriate, update or withdraw an active flight authorisation when new airspace restrictions or traffic information create a conflict. That information may come from air traffic services or, where available, a non-cooperative drone-detection system.
This is more than static pre-flight planning. Nevertheless, its effectiveness still depends on the traffic information available, the service coverage, the participation requirements, the means of detection and the action expected from the operator. EASA’s guidance also makes clear that ending an active flight remains an operator action; it is not expected to be performed automatically by the U-space service provider.
The important question is therefore not whether U-space or UTM can support tactical functions. In some implementations, they clearly can. The question is exactly which function is being provided, against which traffic, with what performance, and who remains responsible for acting on the information.
Without those answers, the word “deconflicted” may be carrying more operational meaning than the underlying service can support.
The aircraft outside the digital picture
The most difficult aircraft for a BVLOS crew to manage is not always the closest one. It is the one that has not yet entered the crew’s operational picture.
The term “non-cooperative” also needs to be used carefully. It should not automatically be interpreted as “illegal”, “hostile” or “irresponsible”. In a surveillance context, it may simply refer to an aircraft that is not providing usable information to the systems supporting the UAS operation. The aircraft may be operating lawfully but without compatible electronic conspicuity. It may be visible to one surveillance source and absent from another. There may also be unknown or unauthorised traffic, but that is only one part of the problem.
The FAA makes the limitation particularly clear in its Aeronautical Information Publication guidance on ADS-B traffic awareness. Pilots are advised that, in some airspace, not every aircraft will be equipped with ADS-B Out or a transponder, and those aircraft will not be visible on an ADS-B In display.
Although that guidance is written for piloted aviation, the underlying limitation is directly relevant to remote operations: a cooperative traffic picture is only as complete as the participating aircraft, surveillance infrastructure and data chain supporting it.
A traffic display should therefore be interpreted as a representation of available surveillance data, not as proof that no other aircraft is present. Each displayed track originates from a source with its own coverage, update rate, latency, integrity and failure modes. A clear screen may indicate clear airspace, but it may also reflect the boundary of what the system can currently see.
That difference needs to be understood by crews, instructors, safety managers and those designing operational procedures. Otherwise, a tool intended to improve situational awareness can unintentionally create an assumption of completeness.
Traffic awareness is not automatically DAA
The appearance of an aircraft symbol on a display does not, by itself, constitute a complete detect-and-avoid capability.
The FAA’s description of the ADS-B Traffic Advisory System provides a useful comparison. ATAS combines ADS-B tracking data with conflict-prediction algorithms and can alert a pilot to potential traffic. However, the FAA expressly distinguishes this capability from TCAS II: ATAS does not issue resolution advisories or provide manoeuvring guidance.
This illustrates the difference between knowing that traffic exists and having a validated system for resolving the conflict.
For BVLOS operations assessed under SORA, tactical mitigation is treated as a complete feedback loop. The current EASA material identifies five functions: detect, decide, command, execute and feedback. Together, they describe the path from initial traffic detection to confirmation that the response has had the intended effect.
Every element matters.
A sensor must first detect the aircraft with adequate range and continuity. The information must then be interpreted to determine whether the track represents a relevant conflict. A decision must be made, either by the remote pilot, automation or a defined combination of both. The avoidance command must reach the UAS through the C2 link. The aircraft must have sufficient performance, navigation integrity, energy and manoeuvring space to execute it. Finally, the system needs feedback confirming whether the conflict has been resolved.
A weakness anywhere in that chain can undermine the tactical mitigation.
Detection range, considered in isolation, is therefore an incomplete performance measure. Operational effectiveness can also be affected by track accuracy, update rate, latency, false or nuisance alerts, interface design, decision thresholds, communication delays and the flight performance of the UAS.
The standards community similarly treats DAA as a system rather than a single sensor or display. EUROCAE ED-271A establishes system-level performance standards for DAA against conflicting traffic for RPAS operating under IFR in airspace Classes A to G. Its scope is not identical to every low-level BVLOS operation, but its system-level approach reinforces an important principle: DAA performance depends on the combined behaviour of multiple components and functions.
NASA’s DAIDALUS reference implementation, developed in connection with RTCA DO-365, provides another concrete example. Its core functions include detection logic, alerting logic and manoeuvre-guidance logic, including guidance for recovering well clear. Again, the distinction is visible: surveillance information is an input to conflict management, not the entire solution.
The human remains part of the architecture
Even a technically capable system can leave important operational questions unanswered.
If the remote pilot is expected to make the final decision, the interface must present the information early and clearly enough to support that decision while the crew is carrying out the rest of the mission. The pilot may already be monitoring aircraft status, navigation performance, C2 quality, payload activity, weather, energy reserves and operational boundaries.
The issue is not simply workload in the general sense. It is whether the human role has been explicitly designed.
Who acknowledges the traffic alert? Who decides that manoeuvring is necessary? Are the criteria defined in advance, or is the crew expected to improvise? Does the system provide guidance, or only traffic information? What happens if the pilot waits for visual confirmation that can never be obtained in BVLOS conditions? Can the UAS perform the commanded manoeuvre without leaving its authorised or safe operational volume?
Research conducted by the FAA into minimum information requirements for UAS DAA traffic displays examined pilots responding to unexpected traffic encounters during a simulated firefighting mission. The study considered display information, suggested manoeuvres, alert location and the loss of an aural alert. It is a reminder that DAA performance cannot be separated from the conditions under which a remote pilot receives, understands and acts on information.
More data on the screen does not automatically create better situational awareness. It can improve the decision only if its meaning, limitations and required response are understood.
Avoiding false defence in depth
UTM and DAA should not be treated as competing approaches. Strategic deconfliction can prevent many conflicts from developing and reduce the number of encounters passed to the tactical layer. DAA and other tactical mitigations can then address the residual risk that planning was unable to remove.
The safety case becomes fragile when the same underlying capability is credited several times.
A single cooperative traffic feed might support planning, airspace awareness and tactical decision-making. If that feed is interrupted, degraded or incomplete, several barriers may disappear simultaneously. On paper, the operation may appear to have strategic deconfliction, real-time monitoring and tactical traffic awareness. In practice, all three claims may depend on the same source.
EASA’s SORA guidance specifically cautions operators and competent authorities to ensure that air-risk mitigations are not counted twice. That warning is particularly relevant where several services are displayed through one interface or depend on a common network, surveillance provider or data-processing chain.
True defence in depth requires more than naming several functions. It requires understanding their dependencies, independence and failure modes.
The questions an operator should be able to answer
Before a BVLOS flight, it is not enough to ask whether traffic information is available. The operator should know what that information represents.
Which aircraft are expected to be visible? Which legitimate users may not appear? Does surveillance coverage extend across the complete operational volume or only part of it? What are the update rate, latency and integrity assumptions? How is an emerging conflict identified? Does the system provide raw traffic, an alert or manoeuvring guidance? Who has authority to command the response? How long will the aircraft take to execute it? What happens if the C2 link or primary traffic feed is degraded? How will the crew verify that the conflict has been resolved?
The answers will vary according to the operation.
A short BVLOS flight inside validated ground-based surveillance coverage is different from a long linear inspection that relies principally on cooperative information. A predictable repetitive operation is different from an emergency-response mission in which routes, priorities and surrounding traffic can change rapidly. Terrain, aircraft performance, airspace structure, surveillance coverage, communications and crew workload all influence whether a proposed tactical mitigation is credible.
One question, however, should always remain visible:
What happens if the conflicting aircraft is not on the screen?
If the answer is limited to the fact that the flight was authorised, notified or strategically deconflicted, the residual airborne collision risk has not yet been fully addressed.
Closing the gap
Strategic deconfliction will be fundamental to the growth of BVLOS operations. It can organise demand, identify incompatible flight intentions, reduce encounter probability and create a shared operating picture among connected participants.
Its value should not lead the industry to assign it a function it has not been designed or approved to perform.
The remaining gap must be addressed through a proportionate combination of airspace structure, operational restrictions, coordination, cooperative surveillance, independent detection where required, clear decision logic, reliable command paths, executable avoidance manoeuvres and feedback confirming that the response has worked.
It also requires precision in the language used by operators, service providers and regulators. Authorised, notified, visible, monitored, deconflicted, separated and DAA-capable are not interchangeable terms. Each represents a different function and a different safety claim.
The future of UTM will depend not only on connecting more aircraft to a common digital environment, but also on understanding the operational significance of those that remain outside it.
Strategic deconfliction can reduce the likelihood of an encounter. It cannot, by itself, resolve the encounter that still occurs.
That is where tactical conflict mitigation has to take over.
(Image: AI-generated Shutterstock image)
Manuel Ignacio Pérez Pan is a UAS operations and unmanned aviation safety professional with more than 4,000 flight hours and operational experience across Europe and Latin America. His work covers BVLOS operations, critical infrastructure inspection, flight testing, system validation, operational risk management and professional UAS training. His postgraduate research in Aeronautical Sciences focused on the implementation of an unmanned traffic management system. He is the founder of BVLOS Safety Academy.
References
- European Union Aviation Safety Agency. Easy Access Rules for Unmanned Aircraft Systems, Revision from June 2026.
- European Union Aviation Safety Agency. Easy Access Rules for U-space.
- Federal Aviation Administration. Unmanned Aircraft System Traffic Management.
- Federal Aviation Administration. UTM Concept of Operations, Version 2.0.
- International Civil Aviation Organization. UTM Guidance: A Common Framework with Core Boundaries for Global Harmonization.
- Federal Aviation Administration. Aeronautical Information Publication, ENR 1.1: ADS-B limitations and traffic awareness.
- Federal Aviation Administration. ADS-B Traffic Advisory System.
- EUROCAE. ED-271A: Minimum Aviation System Performance Standards for Detect and Avoid Traffic for RPAS in Airspace Classes A–G under IFR.
- National Aeronautics and Space Administration. Detect and Avoid Alerting Logic for Unmanned Systems — DAIDALUS.
- Federal Aviation Administration. Minimum Information Requirements for a UAS Detect-and-Avoid Traffic Display under Full-Mission Conditions.
- International Civil Aviation Organization. Global Air Traffic Management Operational Concept, Doc 9854.