UAS Traffic Management 

Conflict Management Model 

FAA-NASA UTM Research Transition Team: Sense and Avoid Working Group 

NASA Co-Lead: Marcus Johnson 

FAA Co-Lead: Jarrett Larrow 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1. Introduction 3 

2. Scope of Document 4 

3. UTM Scenarios and Use Cases 4 

4. Operational Assumptions 6 

4.1 Airspace Environment 6 

4.2 Airspace Cooperative Surveillance 7 

4.3 Meteorological and Topographical Conditions 8 

4.4 UAS Operations 8 

5. UTM Architecture 9 

6. Risks Associated with UAS Operations 10 

7. Conflict Management Model 12 

7.1 Strategic Separation 14 

7.1.1 Flight Awareness Service 14 

7.1.2 Strategic Deconfliction Service 15 

7.1.3 Flight Notification Service 17 

7.1.4 Operation Planning and Operation Planning Service 18 

7.2 Tactical Separation 21 

7.2.1 Conformance Monitoring Service 21 

7.2.2 Conflict Advisory and Alert Service 24 

7.2.3 Dynamic Rerouting Service 26 

7.2.4 Surveillance Service 28 

7.2.5 Geographic Flight Containment 29 

7.2.6 Visibility and Audibility Enhancements 33 

7.2.7 Location Broadcast / Vehicle-to-Vehicle Communication 34 

7.2.8 Ground Surveillance 35 

7.2.9 Detect and Avoid 35 

7.2.10 Collision and Obstacle Avoidance 40 

Appendix A: Off Nominal Conditions 43 

R01: Excursion from Operation Volume 44 

R02: Incursion of Intruding Aircraft into the Operation Volume 47 

R03: Loss of Control 50 

R04: Loss or Degradation of Command, Control, and Communication 52 

R05: Loss or Degradation of UAS Services 54 

R06: Loss or Degradation of Navigation 55 

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1. Introduction 

Integration of Unmanned Aircraft System (UAS) operations into the NAS will present a variety of 

issues and challenges. Both NASA and FAA have activities and initiatives underway to identify 

and respond to a range of challenges and ensure the safety and integrity of the NAS. NASA’s 

Research and Development approach includes supporting the integration of UAS into the NAS in 

the near-term while pioneering the more extensive transformative changes that increasingly 

autonomous aviation systems will bring over the mid- to far-term. FAA’s focus includes both these 

R&D aspects, as well as operational implementation and potential impacts to current NAS 

processes, procedures, and systems. Joint, structured plans and teaming, within the construct of 

the Research Transition Team (RTT), can provide the necessary cross-organizational construct 

to successfully transfer new operational concepts and technologies for commercialization by 

industry, or adoption by the FAA and other federal agencies to help them achieve their missions. 

The objective of the Sense and Avoid Subgroup is to explore operator solutions to ensure that 

unmanned aircraft do not collide with other aircraft (unmanned [UA] or manned). In conjunction 

with Communication and Navigation (C&N) Subgroup, SAA will analyze the effectiveness of 

operational coordination through sharing of intent information in combination and in contrast to 

active avoidance. Also, for each use case identified by the Concepts & Use Cases Working Group 

(CWG) consistent with the phase of operation, SAA will analyze trade-space between sensing 

and detection capability of UA versus the UA’s capability to maneuver and evaluate technology 

options for sharing positioning information in use cases. SAA will also identify potential 

considerations for radio frequency and network capacity, interoperability, density of operations, 

priority of positioning information on technology, reliability, etc. and explore industry wide solutions 

sets for near-term and longer-term operations. 

NASA is spearheading the validation and research of UTM concept elements with its partners 

using combinations of simulations and field trials. The tests are aligned with NASA’s spiral 

development and evaluation schedule of Technical Capability Levels (TCL) that demonstrate and 

evaluate increasingly complex operations. Figure 1 UTM Research Technical Capability Levels 

summarizes these capabilities for UTM. 

Each new TCL extends the capabilities of the previous level. The number of services provided 

and types of UAS operations supported increase. As a set, the successive iterations support a 

large range of UAS from remotely piloted vehicles to command directed UAS and fully 

autonomous UAS. The UTM RTT, recognizing the diversity of operating environments, 

technological areas, and activities, has been broken into four subgroups focused on: (1) Concepts 

and Use Cases; (2) Data Exchange and Information Architecture; (3) Sense and Avoid (SAA); 

and (4) Communications & Navigation. While the research reflected in this document is primarily 

applicable to SAA, it also reflects the work of the Concepts and Use subgroup and integrates the 

other sub teams’ findings. 

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Capability 1 Capability 3 

● Airspace volume use notification ● Beyond visual line-of-sight 

● Over unpopulated land or water ● Over moderately populated land 

● Minimal general aviation traffic in area ● Some interaction with manned aircraft 

● Contingencies handled by UAS pilot ● Tracking, vehicle-to-vehicle, internet 

● Enable agriculture, firefighting, infrastructure connected 

monitoring ● Public safety, limited package delivery 

Capability 4 

● Beyond visual line-of-sight 

● Urban environments, higher density 

● Autonomous vehicle-to-vehicle, internet 

connected 

● Large-scale contingency mitigation 

● News gathering, deliveries, personal use 

Capability 2 

● Beyond visual line-of-sight 

● Tracking and low-density operations 

● Sparsely populated areas 

● Procedures and “rules of the road” 

● Longer range applications 

Figure 1: UTM Research Technical Capability Level. 

2. Scope of Document 

This document describes UTM services and concepts that support the FAA UTM use cases. The 

general conflict management model values the use of redundant mitigation technologies that 

operate over different time horizons to reach a target level of safety for the operation. Separation 

provision contributes to the safety of the overall separation and each participant (USS, UAS, Other 

airspace users) is responsible for ensuring separation is maintained between aircraft. The intent 

of this document is to capture a strategy for combining separation provisions into a conflict 

management strategy that supports safe small UAS operations in the airspace. 

3. UTM Scenarios and Use Cases 

The UTM Use Cases represents the collaborative research efforts between the FAA and NASA 

as joint members of the Unmanned Aircraft System Traffic Management (UTM) Research 

Transition Team (RTT). The packages comprise of 1) Terms and Definitions, 2) Foundational 

Principles, 3) Concept Narratives, 4) Use Cases, 5) Operational Views, and 6) Roles and 

Responsibilities of actors interacting within what is encompassed by the Technical Capability 

Level UTM operating environments. The following should not be considered established policy or 

construed as regulatory in nature. What is presented is meant to communicate the current, agreed 

upon understanding between the FAA and NASA on features of UTM as exemplified through use 

cases and concept narratives for the purposes of supporting joint NASA/Industry Demonstrations, 

UTM Pilot Program, and Industry standards development. 

The concepts and use case working group from the FAA-NASA UTM Research Transition Team 

(RTT) developed a set of use cases to formulate general conceptual elements and support the 

derivation of systems engineering products by the UTM RTT working groups. The Use Cases 

cover a range of predominantly nominal operations, as well as off-nominal scenarios, and the 

main conceptual elements and interactions within them in a UTM environment. Each use case 

details a set of possible sequences and/or interactions between the system and its users that 

occur to achieve the operational goals defined for the environment being explored. Such cases 

enable analyses to identify, clarify, and organize system requirements - including Operation Views 

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(OVs), Information Flows and Data Exchange Diagrams, and Roles and Responsibility Allocation 

Tables. 

Use case scenarios do not prescribe specific solutions for how an operation should achieve a 

required operational goal (e.g., means by which an unmanned aircraft stays within the prescribed 

boundaries of the operation’s associated airspace volume) but rather identify operational 

requirements. This allows the UTM RTT working groups to develop and ultimately specify the 

appropriate supporting performance requirements for each TCL. Table 1 details the use cases 

that form the basis for the conflict mitigation model described in this document. 

Table 1: Summary of UAS Traffic Management Use Cases 

TCL1-1 Two VLOS Operations with Voluntary Use of UTM for Coordination 

TCL2-1 One BVLOS Operation, One VLOS Operation with Voluntary UTM Participation for 

Coordination 

TCL2-2 Two BVLOS Operations near an Airport in Uncontrolled Airspace 

TCL2-3 Priority Operation – Emergency Medical Aircraft in Uncontrolled Airspace 

TCL2-4 BVLOS Operation Conformance Violation from Uncontrolled Airspace into Class D 

Airspace 

TCL3-1 One-Way BVLOS Flight, Separate Landing/Take-Off Locations 

TCL3-2 Negotiation versus Prioritization between Operators Due to Dynamic 

Restriction (Off-Nominal) 

TCL3-3 UAS Interaction with Manned Aircraft in Low-Altitude Uncontrolled Airspace 

TCL3-4 BVLOS Operation Lost-Link Event 

TCL3-5 High Density UTM Operations in Uncontrolled Airspace 

TCL3-6 Last-Mile Rural Deliveries in Uncontrolled Airspace under the Mode C Veil 

TCL3-7 UTM Priority Considerations in Uncontrolled Airspace 

TCL3-8 UAS Operator Loss of Performance Capabilities in Uncontrolled Airspace 

TCL4-1 BVLOS UTM Operation within UAS Facility Maps 

TCL4-2 Historical UTM Information Queries by Authorized Entities 

TCL4-3 UAS Urgency / Distress Condition with Alternate Landing and UTM 

TCL4-4 UAS Volume Reservation in Controlled Airspace 

TCL4-5 Report to FAA due to UAS Flight Incident 

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Foundational principles generated from the use cases that guide the scope of the concepts 

described in this document are as follows: 

● UTM is a separate, but complementary set of services to the Air Traffic Management 

(ATM) system, based primarily on the sharing of information on airspace constraints and 

flight intent. 

● Participation in UTM is required for beyond visual line of sight (BVLOS) UAS operations 

not participating in ATM. 

● UTM services are available in uncontrolled/Class G airspace and in designated areas in 

controlled airspace – initially under 400 ft above ground level (AGL). 

● With UTM, Operators are responsible for the coordination, execution, and management 

of operations, with rules of the road established by FAA. (FAA interacts with UTM only for 

information/data exchange purposes, as required.) 

● UTM requires increasing levels of engagement/interaction with services as the complexity 

of the operations increases. 

● UAS Operators are responsible for ensuring compliance with all FAA regulations. (UAS 

operators can use services (e.g., authentication, weather, communications, aircraft 

tracking, flight planning, and navigation) from third parties, but UAS operators are 

responsible for meeting the regulatory requirements.) 

● UAS are required to meet the performance and equipage requirements established for the 

type of operation and associated airspace volume/route they are undertaking - including 

the ability to contain operations within a specified airspace volume or remain clear of a 

specified volume either through geo-fencing or operational control. 

● FAA has on-demand access to information regarding UTM operations, including flight 

status, aircraft location, and intent information. 

● Other airspace users - manned aircraft operators and UAS VLOS operators – have access 

to information through the UTM system regarding the conduct of UTM operations. 

● FAA may require certain data to be logged / archived by Operators should the FAA and 

other federal entities request that information (e.g., safety, security, or post-hoc analysis 

of events of interest). 

● All UAS operators and/or UAS service suppliers, under UTM construct are responsible for 

tracking their own aircraft and sharing data with other users as required. (FAA does not 

provide track and locate services; however, FAA maintains their authority to manage 

airspace.) 

4. Operational Assumptions 

4.1 Airspace Environment 

Small UAS are defined as unmanned aircraft that are 55 lbs. or less. Small UAS operations will 

be primarily conducted in Class G airspace and authorized areas in Class B,C,D, and E as defined 

in 14 CFR §71 and depicted in Figure 2. 

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Figure 2: Airspace Classes 

Currently, commercial VLOS operations (Part 107) can operate in uncontrolled airspace or in 

controlled airspace within the boundaries of FAA-published UAS Facility Maps without requiring 

direct coordination with air traffic control. The definition provided by the FAA for these maps is 

as follows: 

UAS Facility Maps show the maximum altitudes around airports where the FAA may 

authorize part 107 UAS operations without additional safety analysis. The maps should 

be used to inform requests for part 107 airspace authorizations and waivers in controlled 

airspace. 

Operations in controlled airspace are required to provide notification to air traffic, however when 

the operation is conducted under the maximum altitude of the facility map the Low Altitude 

Authorization and Notification Capability (LAANC) can facilitate automated authorizations without 

requiring direct coordination between the Part 107 operator and air traffic controllers. The facility 

maps and LAANC for Part 107 operations provide insight into potential mechanisms to allow 

BVLOS operations in controlled airspace in the future under a UTM ecosystem. 

4.2 Airspace Cooperative Surveillance 

In remote and rural environments, it is not anticipated that surveillance of manned aircraft will be 

available for most areas of operation within Class G. However, in accordance with 14 CFR 

§91.215, within the Mode-C veil, manned aircraft will provide position reports from the surface to 

10,000 ft MSL within 30 nautical miles of the primary airport within Class B airspace. The FAA 

AIM states in Section 4-1-20(a)(3) that for airborne operations in Class G airspace, the 

transponder should be operating unless otherwise requested by ATC. Furthermore, per §91.225, 

ADS-B Out equipment is required after January 1, 2020 in and above Class B and C airspace, 

and within 30 NM of the large airports listed in appendix D of Part 91. UAS operations in 

authorized areas may make use of cooperative surveillance information. 

Manned aircraft may be equipped with a Mode A transponder, a Mode A/C transponder, or a 

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Mode S transponder with or without ADS-B Out (1090ES or UAT) in the Mode-C veil and in and 

around Class C airspace. Manned aircraft are likely to have no transponder or ADS-B Out system 

in Class G airspace outside the transponder (14 CFR §91.215) and ADS-B (14 CFR §91.225) 

mandated airspace. Even within transponder and ADS-B mandated airspace, aircraft may not be 

operating that equipment, either because the aircraft was not originally certified with an electrical 

system, or the aircraft is operating with an ATC authorized deviation (14 CFR §91.215(d), 

91.225(g)). At low altitudes, 500 ft AGL and below, it is likely that manned aircraft will be operating 

under Visual Flight Rules (VFR) and using a 1200 Mode A code in transponder and ADS-B 

mandated airspace. 

4.3 Meteorological and Topographical Conditions 

UAS operations are initially limited to visual meteorological conditions as specified using the visual 

minima in 14 CFR §91.155. Under Part 107, UAS shall operate during daylight or in twilight (30 

minutes before official sunrise to 30 minutes after official sunset, local time) with appropriate anticollision lighting. Night operations may be authorized if the UAS has enhancements that improve 

visibility or detection during nighttime hours. The UAS operator is expected to determine 

meteorological conditions, remaining in VMC, maintaining VFR visibility minimums, or maintain 

cloud separation minimums for the duration of the UAS operation. UAS operators are expected 

to monitor atmospheric conditions to ensure that operational limitations are not exceeded for their 

UAS with respect to wind, air density, precipitation, and temperature. 

UAS Operators are expected to check terrain clearance during flight planning and monitor 

proximity to the topography during the UAS operation. UAS ground control station equipment may 

be exposed to a variety of different environmental conditions. The GCS equipment may also be 

in weather protected and non-weather protected stationary, ground vehicle, maritime 

environments. GCS equipment may even be part of a mobile ground vehicle. UAS operators shall 

ensure that equipment for the ground control station will be qualified for the appropriate 

environment in which it is expected to operate. 

4.4 UAS Operations 

Operational limitations will be placed on the UAS due to airspace regulations, vehicle 

performance, and/or the technical capabilities of the UAS and USS separation mitigations. For 

operational limitations that are placed on the UAS, the pilot will have access to information and 

controls necessary to ensure operations are conducted within the limitations. The information may 

be from onboard sensors, ground sensors, cloud-based services, or databases. Included in such 

operational limitations would be the status and geographical extent of the command and control 

data link coverage. Operational limits are typically included in an Airplane Flight Manual, Service 

Operating Manuals, and/or Pilot’s Operating Handbook, but other documents may be also used 

for UAS. 

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More details pertaining to the relevant UAS operations considered in the scope of this document 

can be found in the UTM Concept of Operations v1.01

. 

5. UTM Architecture 

UTM is intended to support safe and efficient UAS operations in low-altitude airspace by providing 

information and services to UAS operators and other NAS stakeholders. The five core principles 

of UTM are: (1) only authenticated operations are allowed in the airspace, (2) UAS should avoid 

each other, (3) UAS should avoid manned aircraft, (4) UAS operators should have complete 

awareness of all constraints in the airspace, and (5) public safety UAS have priority within the 

airspace. These principles, as well as the concept's guiding tenet: flexibility where 

possible, and structure where necessary, provide a framework for the development of a UTM 

system that is different from the current ATM system that supports manned aviation. 

The UTM construct utilizes industry's ability to supply services where these services do not exist 

(e.g., uncontrolled airspace). In this construct, the FAA will maintain regulatory and operational 

authority for airspace and traffic operations. Through UTM, FAA will provide directives, 

constraints, and authorizations or restrictions. The FAA will institute operational constraints at any 

time, and the FAA will have on-demand access to airspace operators and situation awareness of 

airspace operations continuously through UTM. 

Figure 3: UAS Traffic Management System Architecture. 

In the UTM architecture, the Flight Information Management System (FIMS) is operated by the 

FAA. It interfaces with the other NAS systems and provides directives and constraints to the UAS 

1 Federal Aviation Administration. “UAS Traffic Management Concept of Operations v1.0”, March 

2018. https://utm.arc.nasa.gov/docs/2018-UTM-ConOps-v1.0.pdf 

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operations via the UAS Service Supplier (USS) Network. The USS could be operated by the UAS 

operators, other commercial, or government entities. The operators use the USS to organize and 

coordinate their operations and meet all constraints and directives from the FIMS system. The 

FIMS system has access to all operations and is informed about any deviations that could have 

an impact on the NAS. 

More details pertaining to the services provided within the UTM ecosystem can be found in the 

UTM Concept of Operations v2.02

. 

6. Risks Associated with UAS Operations 

The conflict management approach to UTM focuses on addressing hazards associated with UAS 

operations. For the purposes of this document, risk will be defined as the combination of frequency 

of an occurrence (often expressed as a probability), and the associated level of severity of the 

occurrence. The consequence of an occurrence will be defined as a harm. The primary categories 

of harm for the UTM conflict management approach are: 

● Fatal injuries to third parties on the ground 

● Fatal injuries to third parties in the air 

● Damage to critical infrastructure 

There are other risks and harms associated with an operation that need due consideration when 

presenting a compelling safety argument to the ANSP, however that is outside the scope of this 

document. UTM considers a performance and risk-based approach to addressing the harms 

associated with a given operation, thus context of the operation environment and the subsequent 

air and ground risk define the risk environment and the conflict management model classifies the 

technology barriers available to a UAS Operator as a means to address the harms and the 

subsequent risk associated with the proposed operation environment. To this end the UAS 

Operator would: define a concept of operations for the missions aligned with their business cases, 

a proposed Area of Operation, identify the harms and develop a safety case utilizing technology, 

procedures, and the operational environment to provide barriers to address the associated risk. 

This culmination of information would be reviewed by the ANSP who would issue a Performance 

Authorization which represents a contract with the UAS Operator allowing for UAS operations in 

accordance with the Concept of Operations within the Approved Area of Operation subject to any 

ANSP prescribed Operation Conditions and Limitations. Therefore, within the Approved Area of 

Operations and subject to any relevant Operation Conditions and Limitations the UAS Operator 

would be able plan missions and conduct operations. The Approved Area of Operations would 

only represent the maximum extent of airspace requested from the UAS Operator that allows for 

an acceptable level of air and ground risk given the safety barriers specified by the UAS Operator. 

Therefore, operations over highly populated areas or within highly trafficked airspace would not 

be within the Approved Area of Operation unless a UAS Operator demonstrated suitable safety 

mitigations to address the risk in those areas. 

2 Federal Aviation Administration. “UAS Traffic Management Concept of Operations v2.0”, March 2020. 

https://www.faa.gov/uas/research_development/traffic_management/media/UTM_ConOps_v2.pdf 

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Figure 4: Airborne and ground risk posed to a UAS Operation. 

The UAS Operator missions would involve submitting a Flight Geography to a USS and working 

with a USS to develop an Operation Volume which defines the intent of the UAS Operator. The 

location of Operation Volumes would consider any air or ground risk spatial or temporal buffering 

to ensure compliance with the performance authorization. The USS would support deconfliction 

of Operation Volumes with other UAS Operators and providing mitigations to support separation 

from manned aviation. The UAS Operator would attempt to accomplish their mission while 

remaining within the Flight Geography and employing tactical mitigations and contingency 

procedures to maintain containment within the Flight Geography and avoid incursions of other 

aircraft within their flight geography. Excursions from the Flight Geography initiate emergency 

procedures as potential risk of airborne collisions with other aircraft and injury to persons or 

property on the ground increases. Areas with adjacent Non-Approved airspace (e.g. Class B 

Airspace) may constitute for an elevation of the emergency procedures to include services from 

the air traffic management system as risk to has increased of airborne collisions with aircraft under 

the services provided by air traffic control. Both the air and ground risk hazards must be identified 

and addressed by the UAS Operator in the development of the safety case and monitored during 

operations to ensure safety for all users of the airspace. 

The primary harm that the conflict mitigation model is addressing is fatal injuries to 3rd parties 

due to an airborne collision. This harm is typically a result of airborne conflicts between aircraft 

with human occupants and unmanned aircraft, however as density of operations increase there 

is the risk that the number of UA to UA conflict avoidance maneuvers will increase and thus will 

increase the possible risk of airborne collisions with passenger carrying aircraft due to loss 

predictable UA flight profiles. Airborne conflicts between non-passenger carrying unmanned small 

UAS pose minimal imminent harm of fatal injuries to 3rd parties in the air. The frequency of 

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occurrence of fatal injuries to 3rd parties in the air is often a function of the density of aircraft, both 

manned and unmanned, in the airspace. 

The secondary harm that the conflict mitigation model is addressing is fatal injuries to 3rd parties 

or property on the ground due to collision. This harm is especially relevant for operations over 

people and operation in, around populated areas, and operation near structures. This harm can 

be a result of direct contact between a part of a UA and a person or structure on the ground or 

can be a result of collateral damage due to an airborne collision. 

It should be noted that some contributing factors, such as atmospheric conditions, communication 

performance, and navigation performance can limit or degrade the effectiveness of the mitigations 

used to address the air and ground risks and therefore considerations should be made as to the 

applicability and limits of the technologies employed for separation in the environment in which 

they will operate. 

7. Conflict Management Model 

USS services follow a conflict mitigation approach like ICAO Doc 9854, “Global Air Traffic 

Management Operational Concept,” in which separation mitigations are divided into strategic 

conflict management and tactical conflict management (e.g. separation provision, collision 

avoidance). Conflict management is applied on three layers, comprising: a) Strategic Conflict 

Management, b) Separation Provision, and c) Collision Avoidance. 

● Strategic Conflict Management aims to reduce the need to apply the Separation 

Provision layer and strategic actions will normally occur prior to departure. 

● Separation Provision is the tactical process of keeping aircraft away from hazards by an 

appropriate separation criterion. 

● Collision Avoidance must activate when the separation provision layer has been 

compromised. 

The UTM Conflict Management model considers a risk-based approach which requires the UAS 

Operator to only employ mitigations that are appropriate for the risk in the environment in which 

they are operating their UAS. The model considers strategic and tactical separation mitigations 

from both the UAS Service Supplier and/or Supplemental Data Service Supplier and the UAS 

Operator and UAS capabilities. A UAS Operator may be able to take advantage from mitigations 

currently present by manned aviation in the airspace if those mitigations are deemed to be 

applicable and acceptable by the FAA (e.g. See and Avoid). This document will focus on the 

contributions that a USS/SDSP and a UAS Operator/UAS contribute to preventing airborne 

collisions. 

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Figure 5: UTM Conflict Management Model. 

The UTM Conflict Management Model considers functions that can only be provided by a USS 

given data exchange requirements of the USS Network and shared responsibilities across UAS 

Operators, function that can be accomplished by an SDPS or a USS to support a UAS Operator 

and functions that are solely provided by the UAS Operator and UAS. Strategic separation 

mitigation occurs prior to departure of the UA, whereas tactical separation mitigations are 

employed once the UA is aloft. It is acknowledged that there may exist a limit to the horizon of 

effectiveness of a USS or SDSP mitigation and therefore it is assumed that collision avoidance 

functions are functionally allocated to UAS capabilities. The limits of the time horizon solely 

depend on the performance of the service and communication means in which the service is 

delivered. Furthermore, even if a high performing and rapid USS/SDSP service is possible the 

potential for degraded lost communication render the need for both strategic and tactical 

separation mitigations being employed by a UAS Operator, unless the risk to the environment low 

enough to warrant the relaxation of this requirement. Due to the size, weight, power, and cost 

limitations of small UAS the UTM Conflict Management model encourages a balance of 

redundancy of mitigations technologies with reliability of individual technologies. A UAS Operator 

may opt to subscribe to a USS service to help accommodate for performance limitations with 

onboard capabilities. For example, a UAS Operator may utilize a Conflict Advisory and Alerting 

Service with a larger coverage area to supplement their onboard detect and avoid system that 

has a limited field of view and range to meet the required performance necessary for safe 

separation in the airspace. The UTM Conflict Management model identifies services and 

technologies that address airspace hazards, airborne hazards, and ground hazards and the 

subsequent section will outline the functionality and use of these technologies to support 

avoidance of collisions with airborne and ground objects. 

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7.1 Strategic Separation 

7.1.1 Flight Awareness Service 

Flight awareness services provide a UAS operator contextual geographic information that aids an 

operator’s awareness of areas which pose airborne and ground hazards and limitations or 

constraints that would impact flight operations. The contextual geographic data, constraints, and 

information can be provided by other data service (e.g. mapping, constraint management); 

however the Flight Awareness service is required to synthesize the data prescribed from 

authoritative sources to provide the operator with an informed awareness of known hazards and 

limitations within a prescribed geographic area. The primary functions of the flight awareness 

service are to: 

● Provide information to a UAS operator regarding airspace and ground constraints to aid 

flight planning 

● Perform constraint management by checking the proposed operation intent against all 

known airspace and ground hazard and/or constraint. 

● Provide an advisory to the UAS operator when the proposed operation intent is impacted 

by a known hazard and/or constraint. 

The use of the Flight Awareness Service is not limited to strategic mitigations, as it can be levied 

by tactical mitigations, however the data, information, and limitations are intended to have longer 

update cycles and therefore are often considered “static” data when used by other services. While 

the Flight Awareness Service is expected to encapsulate authoritative airspace and ground 

constraint data from known FAA sources, advanced capabilities allow for utilizing authoritative 

data from local, regional, and state sources to provide localized information that identified relevant 

hazards for UAS operations conducting missions in a geographic region. The Flight Awareness 

Service is a function that is seen as critical to supporting UAS operations and aligns with the UTM 

tenet that a UAS operators should have complete awareness of constraints in the airspace. While 

there can be many types of airspace and ground constraints, some of the common ones are 

identified in Table 2. 

Table 2: Example Constraints used by Flight Awareness Service. 

Airspace Constraints Ground Constraints 

Dynamic Constraints (e.g. UAS Volume 

Reservation) 

Private Property 

Controlled Airspace and Special Use Airspace Public Gatherings 

National Parks Restricted Areas (e.g. National Monument) 

Local Municipality Restrictions Sensitive Areas (e.g. Prison) 

National Security Restrictions (e.g. Power Plant) Obstacle / Terrain Hazards 

Right of Way Airways (e.g. Power Transmission 

Facilities) 

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7.1.2 Strategic Deconfliction Service 

Figure 6: Depiction of segmented four-dimensional Operation Volumes. 

The deconfliction of intended operation intent (e.g. Operation Volumes) between UAS that are 

subscribed to a UAS Service Supplier (USS) is a core function of UTM that supports the tenet 

that UAS should avoid each other. The underlying deconfliction service is strategic in nature and 

is facilitated by an UAS operator submitting their intended operation volumes to the Strategic 

Deconfliction Service. The Strategic Deconfliction Service compares the proposed intended 

operation volumes with other UAS operator’s operation volumes to identify spatiotemporal 

conflicts. This comparison occurs across all operations within a geographic area that have been 

declared on the USS network. The Strategic Deconfliction Service will notify all UAS operator 

impacted by the spatiotemporal and support the operators in attempting to resolve the conflict. If 

no conflicts are present, the Strategic Deconfliction Service notifies the operator that their 

operational intent is conflict-free, and the operator can proceed with the operation. 

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Figure 7: Strategic deconfliction process flow diagram. 

If a strategic conflict does occur with the planned operation, the Strategic Deconfliction Service 

will notify the operator who is proposing the intended operation and the operator can: 

(1) obtain information pertaining to the nature of the conflict, revise and re-submit a conflictfree operation, OR 

(2) initiate an automated negotiation to the UAS operator(s) in conflict, through the USS 

network, and de-conflict the operations, OR 

(3) proceed with the intended operation, given other tactical separation mitigations are in 

place for their operation. All Operators in conflict would be notified that the conflict exists 

and that tactical mitigations must be used to resolve any realized conflicts between 

identified operations. 

A Strategic Deconfliction Service operates under the following principles: 

● A UAS operation supported by a USS should be free of 4-D intersection (spatial and 

temporal) with all other known UAS Operations prior to departure. 

● A prioritization scheme for operations is needed within strategic deconfliction to 

support various types of operations within an airspace. 

● Negotiation schemes should be part of a strategic deconfliction service to support 

automated mediation between conflicting UAS operations. 

● A strategic deconfliction service shall allow for overlapping operation volumes, given 

that other conflict mitigations are in place. 

The objective of the strategic deconfliction service is to minimize the likelihood of planned airborne 

conflicts between UAS operations. 

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Table 3: Recommended Parameters for an Operational Volume to Support Strategic Deconfliction. 

Field Units Description Example 

ordinal Integer This integer represents the ordering of the operation 

volume within the set of operation volumes. Need not be 

consecutive integers. 

1,2,3 

volume_type string This string represents whether an operation volume is a 

trajectory-based operation (TBOV) or an area-based 

operation (ABOV). 

TBOV, ABOV 

near_structure Boolean This Boolean represents whether the operation volume is 

within 400 feet of a structure 

false 

effective_time_begin String 

($datetime) 

Earliest time the operation will use the operation volume. 

Uses the ISO 8601 format conforming to pattern: YYYYMM-DDThh:mm:ss.sssZ. Seconds may have up to 

millisecond accuracy (three positions after decimal). The ‘Z’ 

implies UTC times and is the only time zone accepted. 

2015-08-

20T14:11:56.118Z 

effective_time_end String 

($datetime) 

Latest time the operation will done with the operation 

volume. It must be greater than effective_time_begin. Uses 

the ISO 8601 format conforming to pattern: YYYY-MMDDThh:mm:ss.sssZ. Seconds may have up to millisecond 

accuracy (i.e., three positions after decimal). The ‘Z’ implies 

UTC times and is the only time zone accepted. 

2015-08-

20T15:11:56.118Z 

actual_time_end String 

($datetime) 

Time that the operational volume was freed for use by other 

operations. Should be populated and stored by the USS. 

Uses the ISO 8601 format conforming to pattern: YYYYMM-DDThh:mm:ss.sssZ. Seconds may have up to 

millisecond accuracy (i.e., three positions after decimal). 

The ‘Z’ implies UTC times and is the only time zone 

accepted. 

2015-08-

20T14:31:56.118Z 

min_altitude_wgs84_ft number($ 

double) 

The minimum altitude for this operation in this operation 

volume. In WGS84 reference system using feet as units. 

max_altitude_wgs84_ft Number 

($double) 

The maximum altitude for this operation in this operation 

volume. In WGS84 reference system using feet as units. 

operation_geography string The type of Geometry. In this case, must be ‘Polygon’ per 

GeoJSON spec. Note that the “coordinates” member is 

validated to be an array of size one. 

beyond_visual_line_of_sight Boolean Describes whether the operation volume is beyond the 

visual line of sight of the RPIC. 

7.1.3 Flight Notification Service 

Flight Notification Service is intended to disseminating information regarding UAS operations in 

each geographic area to other airspace users, non-UAS stakeholders, local, state, and tribal 

governments, and the general public. This service is a strategic mitigation and promotes 

transparency within the UTM system. The medium in which information might reach the end users 

will vary on the use of the information. For instance, an application on a cellular device or tablet 

that provides UTM airspace operations information might be suitable for some users, like general 

aviation pilots, but not for others. Examples of mediums for distributing flight notifications: (1) 

mobile application, (2) webpage, (3) voice broadcast communication, (4) written notice, and/or (5) 

public forum announcement. Typical information that will be shared may vary depending on the 

audience but will likely include the elements for a given geographic area: 

● Density of operations 

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● Expected duration at given density levels 

● Expected maximum UAS operating altitudes 

● Approximate launch/recovery locations 

Advance capabilities may include cockpit displays for manned aircraft which would include 

additional information, like UAS positions, and network-based remote identification for law 

enforcement. Most functions of this service are meant to provide other non-UTM stakeholders 

transparency of UAS operations to raise awareness and ensure that they are active participants 

in contributing to the safety of the national airspace (e.g. incorporate UAS flight notifications into 

preflight procedures for manned aviation). Future capabilities may incorporate a standardized 

density criterion that requires the Flight Notification Service to issue notice of areas where 

manned aircraft must demonstrate vigilance or should consider avoiding due to an elevated air 

risk. In these circumstances the Flight Notification Service would be responsible for monitoring 

density of operations in each area and providing notice by established by the established means 

for manned aviation (e.g. Recommended Minimum Operating Altitude, Notice to Airmen, 

Temporary Flight Restriction, etc.) 

7.1.4 Operation Planning and Operation Planning Service 

Operation planning is a critical safety function supporting UAS flight operations. The objective of 

operation planning is for an UAS operator to define a region of operation, e.g. Operation Volume, 

that meets the needs of their mission while complying with the constraints and limitations of their 

approval to safely operate. The operation plan is developed prior to the operation and indicates 

the volume of airspace within which the operation is expected to occur, the times and locations of 

the key events associated with the operation, including launch, recovery, and any other 

information deemed important (e.g., segmentation of the operation trajectory by time). The 

operation plan as proposed may be impacted by other planned operations (e.g., overlapping 

airspace volumes) or other constraints (e.g., airspace restrictions), therefore the Operator should 

assess all appropriate information affecting the planned operation and make amendments to the 

plan as applicable. The Operator gathers airspace constraints provided by a competent authority 

and any localized airspace restrictions that could affect the proposed flight. 

Operation planning serves as a critical safety function for the UAS operation and can make use 

of strategic mitigation to mitigate air and ground risk, such as: 

● Restricting boundary of Area of Operation to geographic regions with acceptable air 

and ground risk. 

● Restricting time in which operations are conducted to periods in which result in an 

acceptable air and ground risk. 

● Restricting behavior of operation to ensure interoperability with other aircraft, 

compliance with airspace constraints and avoidance of ground obstacles. 

● Restricting exposure or duration of an operation to reduce the likelihood of the air risk 

and ground risk for the Area of Operation 

For low altitude airspace small UAS flight operations, a UAS operator must consider the air risk 

and ground risks associated with their mission. The operation planning safety function is crucial 

to ensuring the safety of the airspace and should consider at least the following factors: 

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● Mission Success and Vehicle Performance 

○ Achievable flight path Trajectory 

○ Minimum required endurance and maximum vehicle range 

○ Command, control, and communication coverage range and quality of service 

○ UAS performance and flight behavior (e.g., turn radius, launch/recovery procedures, 

etc.) 

○ UAS navigation error 

○ Contingency management procedures 

○ UAS Services coverage areas and quality of service. 

● Environmental Conditions 

○ Atmospheric conditions (e.g., direction and magnitude of wind) 

○ Terrain and ground hazards (e.g., Man-made Structures, Foliage) 

● Airspace Conditions and Flight Rules 

○ Airspace structure and flight rules 

○ Approved Area of Operation (e.g. Performance Authorization) 

○ Operation conditions and limitations (e.g. night flights) 

The operation planning safety function can be challenging to address as the environment 

increases in complexity. The awareness of air and ground hazards and a means to validate that 

the safety mitigations are effective at addressing relevant hazards pose an undesirable burden 

on UAS Operators who wish to conduct operations in complex environments. UTM services offer 

an opportunity to assist an UAS Operator in meeting the operation planning safety function for 

complex operation (e.g. BVLOS) and/or operations in a complex environment. A service providing 

operation planning, denoted as Operation Planning Service, supports the UAS operator in 

developing and modifying operation plans to: 

● Avoid overflight of areas of unacceptable ground risk 

● Avoid flight into areas with flight restrictions 

● Avoid flight into areas with unacceptable air risk 

● De-conflict with other UAS operations 

The Operation Planning Service could provide information, advisories, and guidance to UAS 

Operators prior-to, during, and after the planning process of a UAS flight operation. 

To use the Operation Planning Service, UAS operator submits a set of user-defined fourdimensional volumes or trajectories consisting of geographic information and time, that represents 

the physical location of the planned operation. UTM supports more efficient use of the airspace 

by allowing for multiple 4D volumes that are overlapping in time and space to be submitted and 

form a chain of volumes that will be used for a single operation. This chain or set of user-defined 

4D volumes or trajectories that contain the intended flight path of UAS are called a Flight 

Geography. The Operation Planning Service compares the Flight Geography with known hazards 

and constraints in and around the proposed Flight Geography and outputs notification of 

conflicting hazards. 

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Figure 8: Depiction of 4 dimensional segmented Flight Geographies. 

The creation of a Flight Geography can be defined by the UAS Operator, however as the 

complexity of the operation and environment increase UAS Operator may use Operation Planning 

Service to support flight planning. The basic function of the Operation Planning Service is to 

evaluate the suitability of the Flight Geography by: (1) identifying known air and ground hazards 

during the pre-flight phase of an operation, and (2) ensuring that the Flight Geography is properly 

defined (or converted from a trajectory) such to use as a means to communicate intent within 

UTM. More advanced features of the Operation Planning Service may include evaluating the 

fitness of the UAS to fly within the Flight Geography, the automatic refinement of a Flight 

Geography given known hazards, quantification of risk associated with spatial or temporal aspects 

of the Flight Geography, and scheduling and sequencing of operations into a fixed location (e.g. 

Part 135 parcel delivery). These advanced features may require additionally input from the UAS 

Operator regarding the performance of the aircraft, communication and navigation performance, 

contingency management actions, launch/recovery behavior, etc. The service may also other 

utilize supplemental data to provide the appropriate context to evaluate the Flight Geography (e.g. 

atmospheric information). A Operation Planning Service supports UAS operators by considering 

factors required for safe and efficient missions and operates under the following assumptions: 

● All phases of flight of the UAS operation must be contained within a 4D volume of the 

Flight Geography 

● Each 4D volume of the Flight Geography must have a start and end time 

● Contingency locations must be identified for each volume in a Flight Geography (e.g. 

alternate landing location, lost link waypoint, etc.) 

● Contingency locations should be contained within their respective flight volume of a Flight 

Geography, unless in-time Flight Geography modification is supported during flight. 

● An Operation Planning Service must promote efficient and safe use of the airspace during 

flight planning 

Table 4: Parameters Required for Flight Geography. 

Field Units Description Example 

ordinal Integer This integer represents the ordering of the flight 

geography within the set of operation volumes. 

Need not be consecutive integers. 

1,2,3 

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volume_type string This string represents whether an operation 

volume is a trajectory-based operation or an 

area-based operation. 

TBOV,ABOV 

gufi String Globally unique flight identification number 4ce9f71-97e1-414e85a9-118f919aa920" 

effective_time_begin String ($date-time) Earliest time the operation will use the operation 

volume. Uses the ISO 8601 format conforming to 

pattern: YYYY-MM-DDThh:mm:ss.sssZ. 

Seconds may have up to millisecond accuracy 

(three positions after decimal). The ‘Z’ implies 

UTC times and is the only timezone accepted. 

2015-08-

20T14:11:56.118Z 

effective_time_end String ($date-time) Latest time the operation will done with the 

operation volume. It must be greater than 

effective_time_begin. Uses the ISO 8601 format 

conforming to pattern: YYYY-MMDDThh:mm:ss.sssZ. Seconds may have up to 

millisecond accuracy (three positions after 

decimal). The ‘Z’ implies UTC times and is the 

only timezone accepted. 

2015-08-

20T15:11:56.118Z 

actual_time_end String ($date-time) Time that the operational volume was freed for 

use by other operations. Should be populated 

and stored by the USS. Uses the ISO 8601 

format conforming to pattern: YYYY-MMDDThh:mm:ss.sssZ. Seconds may have up to 

millisecond accuracy (three positions after 

decimal). The ‘Z’ implies UTC times and is the 

only time zone accepted. 

2015-08-

20T14:31:56.118Z 

min_altitude_wgs84_ft number($double) The minimum altitude for this operation in this 

operation volume. In WGS84 reference system 

using feet as units. 

max_altitude_wgs84_ft Number ($double) The maximum altitude for this operation in this 

operation volume. In WGS84 reference system 

using feet as units. 

operation_geography string The type of Geometry. In this case, must be 

‘Polygon’ per GeoJSON spec. Note that the 

“coordinates” member is validated to be an array 

of size one. 

7.2 Tactical Separation 

7.2.1 Conformance Monitoring Service 

UTM Services can support UAS operations by providing a UAS operator with enhanced situation 

awareness, safety mitigations, contingency support, and compliance with the requirements 

stipulated under an authorization to operate. On such means of supporting compliance to 

operational requirements is to support an operator’s ability to conform to their Operation Volume 

and provide notifications when they are not in conformance. The objective of the Conformance 

Monitoring Service is to monitor the state of an operation to ensure that a UAS Operator is aware 

of potential deviations from the intended operation intent (e.g. Operation Volume). 

The Operator’s prescribed Flight Geography can be considered a declaration of operation intent 

that they are agreeing to contain their aircraft within. By adding spatiotemporal buffers to the Flight 

Geography, an Operation Volume is defined which can be shared with other airspace users within 

USS network. The intention of conformance monitoring is to (1) notify a UAS operator that they 

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have started to deviate from the declared intent and (2) notify other airspace users when that 

deviation poses a credible hazard to their operations. The operator notification provides the 

opportunity to inject corrective action prior to a prolonged deviation that could impact other 

airspace users. Furthermore, the conformance monitoring serves as a notification and 

communication means to support an Operator’s mitigations to ensure containment of their 

operations to their Authorized Area of Operation. 

During flight planning, the UAS operator develops and shares a Flight Geography with the 

Conformance Monitoring Service. Two additional buffers are imposed on the Flight Geography, a 

Conformance Volume and Operation Volume, to ensure proper separation between UAS 

Operator’s intent is prescribed that accounts for variations in navigation performance, vehicle 

performance, and containment mitigation performance of the UA. The buffers also may consider 

a minimum reaction time necessary to avoid a conflict from other airspace users in the event of a 

Flight Geography breach. The Operation Volume represents a declaration of operational intent 

within the USS Network and is used to notify other airspace users of potential hazards due to the 

proposed operation. Conformance monitoring is a means to support a UAS operator in adhering 

to their Operational Volume by providing notifications and alerts when an operator has deviated 

from this intent. 

Figure 9: Conformance Monitoring Service alerts and notifications. 

During flight planning a UAS Operator submits a Flight Geography to their USS and their USS 

supports the development of an Operation Volume. The Operation Volume is considered a 

declaration of intent that is shared with the USS network for strategic deconfliction and situation 

awareness and serves as an agreement between the USS and UAS Operator as to the extent of 

geographic area that is intended for operation by the UA. The Conformance Monitoring service is 

a means for a USS to support a UAS operator in containing their operation the prescribed 

Operation Volume by providing alerts when an operator has: (1) breached their Flight Geography, 

(2) breached their Conformance Volume, (3) breached their Operation Volume, and (4) persisted 

outside their Flight Geography for an unacceptable duration of time. The Conformance Monitoring 

Service is considered foundational to supporting community-based traffic management as it 

supports tracking, and notification of non-compliant behavior. A Conformance Monitoring Service 

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may eventually be a feature of a broader compliance monitoring function that supports a UAS 

Operator in ensuring that their operation is following the terms of their Performance Authorization. 

This future capability may include monitoring the state of required services, equipage, or operation 

limitations and other regulatory requirements. A Conformance Monitoring Service operates under 

the following principles: 

● UAS Operators shall provide real-time telemetry and state information to a USS, to enable 

the Conformance Monitoring Service to track the UAS 

● A USS provider shall track a subscribed UAS and issue alerts to the UAS Operator when 

conformance to Flight Geography has been lost. 

● A USS must define a Conformance Volume for each Operation Volume of an operation. 

● A Conformance Volume must be contained in all four dimensions within its associated 

Operation Volume. 

● When conformance with operation intent has been lost, the USS shall change the state of 

the operation from “ACTIVE” to “NON-CONFORMING” 

● When compliance with operation intent has been regained, the USS shall change the state 

of the operation from “NON-CONFORMING” to “ACTIVE” 

● If there is a severe deviation from operation intent or the state of the operation remains 

“NON-CONFORMING” for a sufficient duration of time, the USS shall elevate severity of 

the infraction by changing the state of the operation from “NON-CONFORMING” to 

“ROGUE” 

● Operations that enter a “ROGUE” state are considered in breach of the operation intent 

and therefore cannot return to an “ACTIVE” state, rather they must abort their mission. 

NOTE: UAS Operators are encouraged to conduct thorough flight planning, to ensure 

sufficient buffers based on the capability of their UAS and the current and forecasted 

environmental conditions, and utilize additional services (e.g. dynamic re-routing) to 

ensure that they are maintaining compliance to their intended plans, or modifying their 

plans given changing airspace or vehicle conditions to ensure consistency of UAS 

performance during the operation 

● A USS shall announce operation state changes to the UAS Operator who caused the state 

change, other subscribed UAS Operators that are in the local proximity, and the USS 

Network to disseminate the announcement to other UAS Operators conducting missions 

in the local proximity. 

There is an interplay between the Strategic Deconfliction Service and the Conformance 

Monitoring Service which highlights the trade-off between the efficiency and safety of the 

airspace. The Strategic Deconfliction Service encourages UAS Operators to plan operation 

volumes as efficiently as possible to minimize pre-departure conflicts. This typically results in 

planning operations in underutilized airspace or reducing the spatial and/or temporal exposure of 

the operation volumes in the airspace. In contrast, the conformance monitoring service 

encourages UAS Operators to create operation volumes that are sufficiently sized to account for 

the performance of their aircraft and to be cognizant of changing conditions during the operation 

that may require more (or less) spatial and/or temporal exposure of the operation volumes to 

ensure mission success (e.g. atmospheric conditions). UAS Operators should consider “ROGUE” 

operations as an undesired operational state and are encouraged to ensure that the occurrence 

of a “ROGUE” operation is extremely rare. The combination of flight planning, Strategic 

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Deconfliction Service and the Conformance Monitoring Service are foundational to communitybased traffic management and support a UAS operator in designing, de-conflicting, and 

monitoring Operation Volumes to reduce the likelihood of mid-air collisions and containing 

missions within Authorized Areas of Operations. 

7.2.2 Conflict Advisory and Alert Service 

Conflict Advisory and Alert Service supports a UAS operator by providing real-time or near realtime data regarding the proximity to potential conflicting aircraft. The main functions of the Conflict 

Advisory Service are to provide a UAS Operator (or Remote Pilot in Command) informative, 

suggestive, or directive guidance with regards to aircraft that could pose a hazard to their 

operations. This service relies on surveillance data sources to provide awareness of hazards in 

the airspace. In contrast to other separation services (e.g. strategic deconfliction) the conflict 

advisory and alert service is intended to support the resolution of tactical air-to-air conflicts with 

other aircraft, as opposed to deconfliction with UAS operation intent or airspace constraints. The 

Conflict Advisory and Alert Service can utilize surveillance information from the following sources 

(when available): 

● Aircraft position and operation information within USS Network due to non-conformance 

to Flight Geography 

● Aircraft position and operation information within USS Network due overlapping 

Operational Volumes 

● Self-reporting aircraft position from other UAS operators via UAS Reports (UREP) 

● Primary returns from networked surveillance sources (e.g. tactical ground-based radar, 

EO/IR sensor) 

● Secondary returns from networked transponder-based surveillance sources (e.g. 

secondary surveillance radar, ADS-B). 

The Conflict Advisory and Alert Service is considered a tactical mitigation and can be provided by 

a service supplier to support an operator, however, still requires an operator to be engaged in the 

decision to resolve the identified conflicts. 

Figure 10: Functional diagram depicting the Conflict Advisory and Alerting Service. 

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The service is decomposed into four functional elements: (1) Conflict Detection, (2) Conflict 

Tracking, (3) Threat Declaration, and (4) Conflict Guidance. Conflict detection is the primary 

interface for the conflict advisory and alert service to collect surveillance data from different 

sources. This function would establish the integrity, uncertainty, surveillance volume, and 

relevance of aircraft or operation information provided from each surveillance source. The conflict 

detection function would also be responsible for the discovery of surveillance services, quality of 

surveillance service monitoring, and management of performance limitations of surveillance 

sources. The conflict tracking function is aimed at using the relevant surveillance information to 

perform data association and correlation to establish how multiple position reports (from different 

sources and/or over a time series) are coalesced to a single track to present to an Operator. 

Furthermore, the conflict tracking function will determine when tracks are established, stale, lost, 

and/or need to be removed. The conflict tracking function will also assign a track identification 

which may be synonymous with a UAS identification, if known or can be correlated. The conflict 

tracking function will also project a state estimate over a time horizon to establish intent of a 

vehicle if that information is not known or reliable. The threat declaration logic retains and 

manages separation criteria and right of way rules that are applicable to conflicts given the type 

of conflict and the rules or limitations of the airspace. These separation criteria and/or right of way 

rules are then used to evaluate and determine the credibility of an intruding aircraft to pose a 

threat to the ownship UAS. Furthermore, intruding aircraft that are established as credible hazards 

or threats are then prioritized amongst other credible airborne hazards within the airspace. The 

prioritization of the threats also establishes the severity of the threat and whether a threat is 

communicated as a traffic advisory or conflict alert. The severity of a threat aircraft can change 

with the progression of the conflict. In such cases, the threats are declared in order of priority to 

the conflict guidance function. Guidance is provided to the UAS Operator in three different forms 

based on the level of automation available in the service: informative, suggestive, or directive. 

The types of guidance provided are generally distinguished as follows: 

● Informative Guidance will typically provide the necessary information to produce air traffic 

on a map and basic information regarding the state of an aircraft (airspeed, vertical rate, 

call sign, etc.). It provides no explicit maneuver guidance to a UAS Operator. 

● Suggestive Guidance will typically provide additional information to informative guidance 

by indicating of a range of possible maneuvers to avoid a conflict. The UAS Operator 

makes the determination of what action to take based on the options presented and their 

judgement of the nature of the conflict. 

● Directive Guidance will provide a pilot a specific maneuver to resolve a conflict. The UAS 

Operator makes the determination of what action to take based on the maneuver 

presented and their judgement of the conflict. 

An underlying assumption of the Conflict Advisory and Alert Service is that there exists a traffic 

display that depicts the conflict guidance and there exists a human to perform the function of 

determining the resulting maneuver command. The suggestive and directive guidance are 

beneficial in aiding a UAS Operator to more quickly identify and resolve credible threats and 

potentially reduces their workload. Several modes of operation could be considered for a UAS 

Operator’s interaction with their UAS while using this service: 

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● Pilot-in-the-Loop: Pilot views situation awareness display, is provided informative or 

suggestive guidance regarding threat aircraft and serves the function of determining and 

commanding the conflict resolution maneuver 

● Pilot-on-the-Loop (Manage by Consent): Pilot views situation awareness display, is 

provided directive guidance regarding maneuvering against threat aircraft and serves the 

function to command the resolution maneuver 

● Pilot-on-the-Loop (Manage by Exception): Pilot views situation awareness display, is 

provided directive guidance regarding a planned automated maneuver command against 

a threat aircraft and serves the function to negate the execution of the resolution 

maneuver, if inappropriate. 

The pilot-off-the-loop, or automated command and execution mode of operation is possible given 

an automated dynamic rerouting function (either as a service or UAS capability). This mode of 

operation would remove the pilot’s ability to intervene in conflict resolution and would be subject 

to the guidelines, regulations, and limitations imposed by the FAA. 

7.2.3 Dynamic Rerouting Service 

Dynamic Rerouting Service supports a UAS operator by providing modifications to intended 

operation volumes and directive guidance to change flight path to minimize the likelihood of 

airborne conflicts and maximize the likelihood of conforming to airspace restrictions and 

maintaining mission objectives. The Dynamic Rerouting Service is a tactical service that is an 

extension of pre-departure strategic deconfliction by supporting an Operator with conflicting intent, 

performing automated prioritization and negotiations when intent is in conflict. Dynamic Rerouting 

Service requires a higher level of automation, over that of strategic deconfliction, given that the 

service it is a tactical service employed while the UA is aloft. Furthermore, this service supports 

an UAS operator to recover from excursions from their Operation Volume by providing 

preventative Operation Volume and flight path modifications that capture the unintended behavior 

and support the UAS operator in returning to the mission. The Dynamic Rerouting Service will 

more readily account for predicted excursions due to atmospheric conditions (e.g. winds) or preplanned contingency actions (e.g. loss of command and control link). In addition to support flight 

path and operation intent modifications the Dynamic Rerouting Service can also support air-to-air 

conflict resolution (if surveillance is available) by leveraging the Conflict Advisory and Alert 

Service features to provide a conflict resolution flight path maneuvers and operation volume 

modification. 

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Figure 11: Functional diagram depicting the Dynamic Rerouting Service. 

The Dynamic Rerouting Service denotes a higher level of automation that is reliant on several 

other functional services to support the automation. Conflict Advisory and Alert Services and 

Surveillance Services provides the information and possibly maneuver recommendations against 

intruder aircraft, whereas Strategic Deconfliction Services and Flight Awareness Services provide 

information, intersection detection, and negotiation support against resolving conflicts with other 

UAS Operation Volumes and airspace constraints. Conformance Monitoring Services provide 

UAS state information for context on when other UAS are out of conformance and boundaries of 

the UAS ownship for consideration in conflict resolution. Ownship position, state, intent, remaining 

endurance, aircraft performance, onboard geofence boundaries, and other state and operation 

information are needed from a UAS Operator to support the Dynamic Rerouting Services. 

Additionally, the Dynamic Rerouting service relies on a UAS Operator and/or the Strategic 

Deconfliction service to announce the operation plan modification to the USS Network. While the 

Dynamic Rerouting Service is intended to be a higher level of automation, UAS Operator 

interaction can still be supported in a variety of different ways, such as: 

● RPIC submits request to the Dynamic Rerouting Service for a conflict-free path given 

revised mission parameters, while UAS is aloft 

● Maneuver guidance presented to RPIC due to identified airborne hazard (e.g. intruder 

aircraft) or ANSP directive (e.g. Dynamic Restriction) and RPIC approves maneuver (e.g. 

manage by consent) or doesn't intervene (e.g. manage by exception) 

Additional services may be included to interface with the Dynamic Rerouting service, (such as 

Communication Services, Weather Services, Dynamic Risk Reduction Services, etc.) to further 

provide context to the selection of a conflict resolution or recovery maneuver. The Dynamic 

Rerouting Service is assumed to operate under the following principles: 

● A UAS operation modification supported by a USS should be free of 4-D intersection 

(spatial and temporal) with all other known UAS Operations when vehicle is aloft. 

● The strategic deconfliction prioritization scheme for operations is for dynamic rerouting to 

support various types of operations within an airspace. 

● A dynamic rerouting service shall minimize airborne conflicts and seek to reduce 

intersections of 4D operation volumes 

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● A dynamic rerouting service shall provide operation plan modifications to the USS 

consistent with and in the event of pre-programmed contingency actions taken by the UAS 

● A dynamic rerouting service should serve mission objectives 

● A dynamic rerouting service shall allow for overlapping operation volumes, given that other 

separation mitigations are in place. 

The Dynamic Rerouting Service can reduce the performance burden on a detect and avoid 

capability by networked-based surveillance infrastructure to extend the time horizon of conflict 

detection and resolution. In addition, the Dynamic Rerouting Service provides contextual 

airspace, operations, and constraint information in the maneuver selection process that takes into 

consideration the airspace environment (e.g. air traffic, airspace constraints, ground constraints, 

weather, etc.). While many of the dynamic re-route features could be developed as automation 

onboard the UA the contextual airspace environment information is readily dynamic and often not 

available onboard the UAS. The Dynamic Rerouting Service offers a means to offload the 

requirement of onboard automation from having to account for the airspace environment in 

complex environments. A Dynamic Rerouting Service does not remove the need for onboard 

tactical separation mitigations (e.g. DAA) but rather reduces the likelihood of needing to utilize 

such a capability in operations. 

7.2.4 Surveillance Service 

The Surveillance Services consist of set of strategic and tactical services that can support air risk 

assessment for safety case development, support pre-departure flight planning with airspace heat 

maps based on common traffic patterns, and support tactical flight operations by providing realtime tracking information of air traffic for a given geographic area. Surveillance services consist 

of two primary means of collecting information regarding airborne hazards: terrestrial surveillance, 

and airborne surveillance. Surveillance technologies typically will either depend on transponder 

technology (cooperative) or will be independent of transponders or additional equipment onboard 

an aircraft (non-cooperative). Data for the Surveillance Service can be provided from a single 

sensor, a network of sensors, or sensors fused from different sources. 

Table 5: Examples of surveillance technologies. 

Non-cooperative Cooperative 

Airborne Airborne Radar on UAS, 

UAS Reports (UREP)3 

, 

EO/IR Sensors 

Vehicle-to-Vehicle 

Communication, ADS-B 

(air-to-air), Remote ID 

Terrestrial Primary Ground Radar, 

EO/IR Sensors, 

RF Sensors 

Secondary Ground Radar 

3 Rios, Joseph L, Irene S. Smith, David R. Smith, UAS Reports (UREPs): Enabling Exchange of Observation 

Data Between UAS Operations. NASA Technical Memorandum. NASA/TM-2017-219462. February 2017. 

http://hdl.handle.net/2060/20170003878 

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The Surveillance Service serves to support UAS operators throughout different phases of 

operation. 

Safety development using a Surveillance Service can provide UAS Operators with historical 

airspace density maps, common aircraft routes and traffic patterns, and quantify air risk due to 

existing airspace users for a given geographic area. This historical data can offer insight into 

seasonal, monthly, weekly, and hourly trends in use of the airspace, and help a UAS Operator 

identify when periods of the day are typically underutilized. This capability allows UAS operators 

awareness of the existing likelihood of potential airborne conflict while conducting operation in a 

given geographic area. Thus, empowering UAS operators to determine appropriate strategic and 

tactical mitigations that are consistent with the level of air risk for that airspace. This data can also 

aide the regulator in establishing the target level of safety for a given airspace. 

Flight Planning using a Surveillance Service can provide an UAS Operator awareness of areas 

within locations in the airspace that would yield a higher likelihood of air traffic and develop 

Operation Volumes that consider the airspace structure, common routes of the airspace, and 

common times of day when the airspace is underutilized. Advanced features of this service could 

offer pre-departure risk profiles of the airspace given trend analysis from historical data, allowing 

and operator to use risk-based Go/No Go criteria to determine if the pre-departure risk is low 

enough to support a successful mission. This Surveillance Service supporting flight planning can 

aid a UAS operator in compliance with their Performance Authorization. 

Real-time Detection using a Surveillance Service is a capability that allows for a UAS Operator 

to gain a more complete awareness of the airspace they are using to conduct UAS operations. 

The real-time aspect of the service supports other services, like Conflict Advisory and Alert 

Service and Dynamic Rerouting, to provide support in conflict detection and resolution. This 

service in conjunction with an Authentication and Authorization service can also support the 

identification of aircraft that are non-participants of UTM. 

7.2.5 Geographic Flight Containment 

When a UAS Operator conducts flight planning they design an operation which has an acceptable 

air and ground risk and they may employ supporting services and capabilities help contain the 

UA to that operation plan. Geographic flight containment is a capability that supports a UAS 

Operator by (1) providing alerts to the Operator of a potential of deviation from a geographic area 

and (2) by providing an onboard forcing function to prevent a UA from blundering outside of a 

geographic area. Geographic flight containment is a location-based service and a subset of 

capabilities associated with geographic virtual fencing (also denoted as geo-fencing). Geographic 

flight containment is characterized in two ways: 

● Static Geographic Flight Containment is onboard and ground-based containment 

mitigations that are based on geographic volume(s) that are static for the entirety of the 

UAS operation. An Authorized Area of Operation specified in the Performance 

Authorization is an example of a static geographic volume in which a containment 

mitigation could be applied. The Static Geographic Flight Containment mitigation can be 

viewed as a failsafe to ensure that a UA halts forward progression from the defined 

geographic containment boundary and the UA returns to an acceptable location within the 

geographic boundary. The static geographic flight containment mitigation will likely require 

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a higher level of reliability if the geographic boundary lies adjacent to areas of elevated air 

or ground risk. 

● Dynamic Geographic Flight Containment is onboard and ground-based containment 

mitigations that are based on geographic volume(s) that can change during an UAS 

operation. The Flight Geography is an example of a geographic volume that can change 

during a flight in which a containment mitigation could be applied. The Dynamic 

Geographic Flight Containment mitigation can be considered a means to support 

containment of a UA to its announced intent which would reduce the likelihood of a nonconforming operation. 

It should be noted that a complementary capability of geographic flight containment is a boundary 

enforcing a geographic flight restriction. A geographic flight containment mitigation will confine a 

UA into a geographic area, whereas a geographic flight restriction mitigation will restrict entry of 

a UA from a geographic area. These capabilities may have similarities in functionally but are 

fundamentally attempting to achieve different objectives. 

The geographic flight containment mitigation should define a preventative and recovery threshold 

in which to apply the mitigations that are wholly constrained within or equivalent to the desired 

volume of containment. For the dynamic geographic containment, the preventative and recovery 

thresholds would be contained within the Flight Geography. These thresholds define actions to 

be taken if the UA blunders beyond the threshold. If a UA crosses the preventative threshold, 

● The geographic flight containment mitigation MUST issue a declaration to the UAS 

Operator that action is necessary to avoid an excursion from the volume of containment 

(e.g. Flight Geography). 

● The geographic flight containment mitigation MUST initiate a course correction procedure 

to maintain the UA position within the volume of containment. This initiation can be 

facilitated by an informative, suggestive, or direct alert to a UAS Operator, or an automated 

response by onboard capabilities on the UA. 

● The preventative threshold SHOULD consider atmospheric conditions, UA characteristics 

(e.g. speed, heading, climb rate, etc.), and navigation error in its definition and can be 

spatial and/or temporally defined. 

● The preventative threshold MUST be no larger than the recovery threshold. 

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Figure 12: Relationship between Flight Containment Capability and Conformance Monitoring Services. 

Simple implementations of a preventative threshold may be statically defined a priori launch of 

the UA, whereas more advanced capabilities may incorporate dynamically changing preventative 

thresholds. While a preventative threshold represents the initiation of a corrective maneuver to 

prevent the UA from breaching the volume of containment (e.g. flight geography), a recovery 

threshold represents the point at which the aircraft can no longer prevent an excursion from the 

containment volume. At this threshold, contingency action is necessary to arrest UA forward 

progression outside the containment volume and a recovery maneuver is required to return the 

UA inside the containment volume. If a UA crosses the recovery threshold, 

● The geographic flight containment mitigation MUST issue a declaration to the UAS 

Operator that a contingency action is occurring to recover the UA due to an excursion from 

the volume of containment (e.g. Flight Geography). 

● The geographic flight containment mitigation MUST initiate a corrective action to arrest 

forward progression of the UA position outside the volume of containment and return the 

UA to with the volume of containment. This initiation is likely an automated response by 

onboard capabilities on the UA. 

● The recovery threshold SHOULD consider atmospheric conditions, UA characteristics 

(e.g. speed, heading, climb rate, etc.), and navigation error in its definition and can be 

spatially and/or temporally defined. 

● The corrective threshold MUST be no larger than the respective volume of containment 

(e.g. Flight Geography). 

The geographic flight containment mitigations can implement functionality onboard the UA and 

on the ground systems of the UAS, however due to the loss of command and control link events 

an onboard mitigation is a required capability of any geographic flight containment system. 

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Common mitigation strategies currently used by geographic flight containment systems to date 

include heading changes, climb or descend to an altitude, hover in place, navigate to a fixed 

location, and deploying a parachute. Geographic flight containment mitigations are expected to 

operate under the following principles: 

● Navigation Data Integrity, Availability, and Accuracy Monitoring is necessary to 

ensure the validity, timeliness, accuracy, and security of the data used to determine that 

flight containment action is necessary. 

● Airspace Displays are required to maintain an UAS Operator’s situation awareness to 

their UA proximity to geo-fence boundaries and actions taken as a result of excursions. 

● Conformance Monitoring is a necessary capability for detecting crossing preventative 

and recovery thresholds and excursions from the volume of containment. 

● UAS Operator alerts are required to maintain a UAS Operators situation awareness and 

should be factored into the definition of the preventative and recovery thresholds if UAS 

Operator response is expected. 

● Corrective Action is expected when breaching a threshold and latency and command 

and control data link should be considered in the threshold definitions if UAS Operator 

response is required. 

● Reliability and Security should be factored into the development of geographic flight 

containment mitigations such that design considerations are made to improve the 

resilience (to factors like interference), reduces the dependencies on external 

infrastructure or internal systems of the UAS and consider threat planes associated with 

security threats to the threshold definitions, monitoring, or corrective maneuver initiation. 

Considerations like independence of the navigation source from the UA autopilot are an 

example of possible resilience being added to the capability. 

Table 6: Recommended Parameters for Flight Containment Capability. 

Variable Name Type Description 

geoFenceAvailable_nonDim INTEGER 0: Non-Available, 1: Available 

geoFenceEnable_nonDim INTEGER 0: Disable, 1: Enable 

geoFenceStartTime INTEGER Time at which geofence is enabled in Coordinated Universal Time 

(UTC). Use ISO 8601 format conforming to pattern: YYYY-MMDDThh:mm:ss.sssZ. Seconds must have up to millisecond accuracy 

(three positions after decimal). The ‘Z’ implies UTC time and is the 

only time zone accepted. 

geoFenceEndTime INTEGER Time at which geographic fence is disabled in Coordinated Universal 

Time (UTC). Use ISO 8601 format conforming to pattern: YYYY-MMDDThh:mm:ss.sssZ. Seconds must have up to millisecond accuracy 

(three positions after decimal). The ‘Z’ implies UTC time and is the 

only time zone accepted. 

geoFenceType_nonDim INTEGER 0: Circular- Point and Radius, 1: Polygon 

geoFenceMinAltitude_ft FLOAT Minimum defined altitude of geographic fence (ft) 

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geoFenceMaxAltitude_ft FLOAT Maximum defined altitude of geographic fence (ft) 

geoFenceCircularPointLat_deg FLOAT Latitude of circular origin point of geographic fence (deg) 

geoFenceCircularPointLon_deg FLOAT Longitude of circular origin point of geographic fence (deg) 

geoFenceCircularRadius_ft FLOAT Radius of circular geographic fence (ft) 

geoFenceDynamicPolygonPoint_deg STRING Specify dynamic location of polygon vertices in the following format: 

”[Lat_1,Lon_1],[Lat_2,Lon_2],....[Lat_n,Lon_n]" (include quotation 

marks). 

This is a time dependent variable (UTC time stamped), specify 

“geoFenceDynamicPolygonPoint_deg” as many times as the polygon 

shape changes during the flight (e.g. for a fixed polygon geofence it’ll 

have the same values of Lat_n, Lon_n all along the flight). 

Report at least seven decimal degrees. (deg) 

7.2.6 Visibility and Audibility Enhancements 

Visibility and audibility enhancements address the risks associated with airborne conflicts and 

injury or death to persons on the ground. These typical represent passive mitigations that rely on 

other parties to initiate resolution of a conflict and is considered a good practice to aid the see 

and avoid mitigation of manned aircraft and persons on the ground. There are two main 

mitigations that have been identified to support increasing the situation awareness and acuity of 

others in the proximity of a UA: anti-collision lighting, and audible broadcast alerting. Future work 

is needed in defining standards around active mitigations, such as tactical and audible alerts, to 

raise situation awareness of the UAS Operator, while using supporting conflict management 

services or capabilities. 

Anti-Collision Lighting. Under Part 107 regulations you can fly during daylight hours (30 minutes 

before official sunrise to 30 minutes after official sunset, local time) or twilight with the appropriate 

anti-collision lighting (107.29). Furthermore, an operator can seek a waiver under Part 107 to 

operate the UA at night, under reduced visibility, or beyond visual line of sight, which would also 

warrant the use of the appropriate anti-collision lighting. Under Part 107, the performance of the 

anti-collision lighting must be such that the light is visible for three statute miles or more. Anticollision lighting is aviation red or aviation white and either blinking or strobing, as opposed to UA 

navigation lights that are often a solid red, green, and/or white. While not required during daylight 

hours, anti-collision lighting may be used to increase the likelihood of a manned aircraft or other 

remote pilots to see and avoid the UA. Further industry standards may consider establishing 

lighting patterns to provide a visual means to alert other airspace users of an off-nominal or 

emergency UA condition. 

Audible Broadcast Alerting. While not required under existing Part 107 regulation, the need for 

BVLOS operations to employ an automated safe landing capability is warranted when operations 

occur over or near populated areas, and/or over a gathering of people. An automated safe landing 

capability considers two primary factors to reduce the risk to people on the ground: (1) avoiding 

people and/or property during landing (e.g. obstacle avoidance), (2) raise situation awareness of 

persons in landing area to allow for time to vacate. The latter factor can be facilitated in a strategic 

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means by pre-designating a secure landing location, or tactical means by visual (e.g. lighting) or 

audible (e.g. speakers) mitigations. Audible broadcast alerting can be implemented as a failsafe 

to provide an alert to persons at risk due to the descent or landing of the UA. Performance of the 

audible broadcast is dependent on the navigation precision, altitude, rate of descent, proximity 

and expected mobility of the persons at risk. 

7.2.7 Location Broadcast / Vehicle-to-Vehicle Communication 

Location broadcast is typically related to UAS remote identification; however, the presence of the 

capability may also enable situation awareness of UAS traffic to other users of the airspace. The 

suitability to support separation using a location broadcast is dependent on the performance of 

the broadcast, security, reliability, and availability of the broadcast, and UA equipage 

requirements. There may be two means to receive location information: (1) transponder-based 

broadcast or network-based broadcast and/or (2) vehicle-to-vehicle communication. To support 

conflict management the broadcast will need to provide information necessary to derive the 

following data: 

• Current UA position prescribed in Latitude, Longitude and Altitude 

• Current UA flight course 

• Current UA ground speed 

• Current UA health and state (e.g. failure-mode, emergency) 

• UA unique identifier to correlate UA with operational information 

Additionally, including information such as UA intent in the position broadcast would improve the 

performance of conflict resolution. The performance, reliability, security, and availability of the 

position information will determine the suitability for use as a conflict mitigator. Low performance 

and reliability position broadcast information (e.g. Remote ID) may only serve as situation 

awareness information, whereas position broadcast information with higher reliability and 

performance (e.g. vehicle-to-vehicle communication) may serve to support detect and avoid or 

collision avoidance conflict resolution mitigations. Standards development is ongoing in 

supporting Remote Identification position sharing that is specific to a transponder-based 

broadcast and a network-based broadcast. The remote ID transponder-based broadcast can 

support air-to-air position sharing with other aircraft that operate in geographic areas or at 

altitudes that are not readily supported by a network. Limitations in transmit power and allowable 

RF frequencies may limit the range of this air-to-air broadcast to a proximity near the UA. Networkbased remote ID broadcast focuses on leveraging network infrastructure to support position 

sharing and therefore both the UA and the other airspace users are required to participate in the 

network to benefit from the information. Network-based remote ID broadcast may extend the 

range in which positions can be shared, but at the cost of limiting the availability of the information 

to areas in which have network coverage. 

Vehicle-to-vehicle (V2V) communication is a bi-directional means of sharing information between 

two aircraft in proximity of each other. V2V may service many different purposes beyond what is 

necessary for safety in the UTM conflict management model (e.g. remote identification), however 

for the purposes of this document V2V will focus on communicating: (1) position information to 

support situation awareness, (2) aircraft state information to support collision avoidance, and (3) 

operation information to support contingency management. Future uses of V2V may support 

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communication between the vehicle and infrastructure to support obstacle avoidance or vertiport 

operations, and/or sequencing and spacing between UA during higher density proximity 

operations (e.g. corridors). 

7.2.8 Ground Surveillance 

To support safe separation from other aircraft UAS Operators may employ a ground surveillance 

capability. Ground surveillance can be accomplished by visual means (e.g. visual observer), or 

digital means (e.g. ground-based radar, camera system, radio frequency tracking) and requires 

communication with the remote sensor that is accomplishing the surveillance. Ground 

surveillance capabilities can be defined as a sensor that detects non-cooperative or cooperative 

traffic. Where cooperative traffic are those in which data sharing exists between the aircraft and 

the surveillance sensor (e.g. local ADS-B receiver) and non-cooperative traffic are aircraft in which 

no data sharing technologies are present. The ground surveillance capability is managed and 

operated by the UAS Operator and is distinctly different from a networked surveillance service 

which can be offered by a service supplier. Ground surveillance accomplishes the detection and 

tracking of airborne objects and can also support a UAS operator in the evaluation, prioritization, 

and threat declaration of airborne traffic that poses a threat to the UAS operation. Ground 

surveillance can contribute to the overall detect and avoid solution of a UAS Operator to meet 

their regulator requirement (e.g. 14 CFR § 91.113). Effective surveillance capabilities should 

provide the following minimum information to the operator about nearby traffic in potential conflict: 

course, ground speed, altitude, position (latitude/longitude). 

7.2.9 Detect and Avoid 

The UTM service-based architecture supports UAS Operators in ensuring safe separation from 

other aircraft by offering services that raise situation awareness, provide alerting, and/or provide 

directive guidance and commands to resolve conflicts. While the services can offer a UAS 

Operator valuable safety benefit in remaining separated from other aircraft and obstacles, the 

services alone do not preclude the need for a tactical detect and avoid (DAA) capability. Service 

providers can: (1) supersede certain required DAA or UAS Operator functionality, (2) supplement 

existing DAA functionality to enhance performance (or reduce performance requirements on the 

UAS equipment) and (3) provide contextual data to UAS DAA equipment that exogenous to its 

sensor suite. In this regard UTM services are complementary to UAS DAA capabilities and can 

be beneficial to UAS Operators to comply with regulatory and safety requirements using low size, 

weight, power, and cost vehicles. 

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Figure 13: Example of separation strategy including USS Services and UAS capabilities. 

The interplay between UAS Services and UAS capabilities in resolving airborne conflicts can be 

depicted along a conflict timeline. Figure 13 depicts an example of different services and 

capabilities supporting a UAS Operator in ensuring safe separation. Notably, each service and 

capability has slightly different objectives corresponding to their function and their applicability on 

the conflict timeline. For instance, at larger time to collision a Conflict Advisory and Alert Service 

may be informing to the UAS Operator of conflicts with the objective to resolve the conflict with 

minimal deviation from the current flight path, whereas a detect and avoid capability would be 

trying to keep the UA at a miss distance larger than a prescribed separation criterion, and a 

collision avoidance system has the objective to avoid a near mid-air collision to a different 

separation criterion. UTM Services may factor in more contextual information about the airspace, 

such as no-fly zones, to aid in compliance with regulatory requirements, whereas a collision 

avoidance capability may focus only on means to create as much distance as possible between 

aircraft to avoid a collision, regardless of the airspace context. The conflict timeline in Figure 13 

is notional and the effective time horizon of each mitigation may vary based performance. 

Furthermore, the time horizon of each mitigation may overlap and the initiation of the mitigation 

may vary based on the what hazard is in conflict with the UA (e.g. timeline may vary if it is a 

manned aircraft vs. a static obstacle). In the UTM conflict mitigation model concept of detect and 

avoid capability can be decomposed into to safety functions: Detect, Track, Evaluate, Prioritize, 

Declare, Determine Action, Command, Execute, and Communicate. The Return-to-Course 

function is typically viewed as a navigation function rather than a conflict mitigation safety function, 

however for the context of this document it is assumed that it is applicable within the UTM Conflict 

Management model. Several safety functions can be accomplished using UTM services (e.g. 

surveillance, conflict advisory and alert, dynamic re-routing) as a mitigation and/or UAS 

capabilities as a mitigation (e.g. detect and avoid system). Typically, the safety function of detect 

and avoid can be partitioned into a self-separation function and collision avoidance function, 

however for the purposes of this document self-separation will be denoted as a detect and avoid 

(DAA) capability and collision avoidance (and obstacle avoidance) will be considered a separate 

function and will be addressed in subsequent sections. It is noteworthy that detect and avoid and 

collision avoidance share similar sub-functions and could also share similar services, sensors, 

and/or capabilities. The subsequent discussion will focus on UAS detect and avoid capabilities. 

For UAS operations the US national airspace often provides few guarantees as to the nature of 

the potential airborne conflicts that could be experienced during a UAS operation. Existing 

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requirements imposed on certain airspaces might increase the likelihood of more uniform 

equipage however there are exceptions to existing requirements and extenuating circumstances 

also can occur within these airspaces which motivates the need for a UAS detect and avoid 

capability when operating beyond visual line of sight. In lower risk environments UTM services 

may be sufficient to comply with see and avoid requirements for a UAS operating BVLOS, 

however in moderate to high risk environments it is generally understood that a collision 

avoidance system is required in conjunction with a UTM separation services and/or UAS DAA 

capability that meets the appropriate performance requirements. A DAA capability should be fit 

for purpose, only imposing requirements that are consistent with risk posed by the operation within 

the respective operational environment, and address airborne hazards existing from cooperative 

(e.g. transponder equipped) and non-cooperative traffic. A DAA capability must consist of the 

following elements: 

● Sensors to detect non-cooperative airborne traffic (e.g. manned and unmanned) 

● Sensors to detect cooperative airborne traffic (e.g. manned and unmanned) 

● A tracking system that includes track initialization, data correlation, and track 

management, and incorporates multi-sensor information in the data correlation. 

● Threat detection, prioritization, and alerting logic based on quantifiable separation 

standards 

● An airspace informative display that provides contextual airspace and environmental 

information, traffic information, and advisory, alerts, and notifications of airborne hazards. 

(note alerting may vary based on the mode of operation: pilot-in-the-loop, pilot-on-theloop, pilot-off-the-loop) 

For DAA capabilities with higher level automation, suggestive and/or directive conflict resolution 

commands may be included as part of the airspace display capabilities or automated response 

may notify the remote pilot after an automated conflict resolution maneuver has been commanded 

or executed. When determining a course of action, a conflict resolution algorithm should consider: 

the threat aircraft, proximal traffic, airspace constraints, vehicle performance, environmental 

conditions, geographic containment, right-of-way rules, and separation standards. 

Table 7: Example surveillance sensors for a DAA capability. 

Sensors 

Non-cooperative Cooperative 

Airborne Radar 

Ground-based Radar 

Acoustics 

Sonar 

Electro-optical 

Infrared 

Laser Systems / LIDAR 

Motion Detection / Cameras 

Mode A/C/S Transponder 

ADS-B In 

Vehicle-to-Vehicle Communication 

(e.g. DSRC, C-V2X) 

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Table 7 provides example sensor technologies that have been proposed to address both the noncooperative and cooperative airborne hazards. For small UAS there are practical considerations 

with respect to the size, weight, power, and cost of equipping with the necessary sensors to avoid 

airborne hazards and therefore UAS operators should consider supplementing UAS DAA 

capabilities with UTM separation services to meet any relevant regulatory safety requirements 

with regards to a conflict management strategy. 

Since different sensors, algorithms, and modes of operation may be suitable to meet the needs 

of a DAA solution given the environment and conditions in which an operation is conducted it is 

useful to abstract key measures that could be used in evaluating the effectiveness of a DAA 

solution. The measures noted in Table 8 and Table 9 can be used to form the basis of a 

performance standard around different types of technologies that contribute to a DAA solution. 

Table 8: Measures of performance for DAA solutions. 

Measure of Performance Description 

Detection 

Detection Range The effective ranges that objects can be detected. This is often a mapping of 

detection range as a function of radar cross section. 

Detection Range Accuracy The position error associated with the detections. 

Field of Regard - Azimuth The horizontal angle describing the total area that can be captured by a movable 

sensor. 

Field of Regard - Elevation The horizontal vertical describing the total area that can be captured by a movable 

sensor. 

Azimuth Accuracy The error associated with the azimuth measure of the field of regard. 

Elevation Accuracy The error associated with the elevation measure of the field of regard. 

Time-to-Track The time it takes to establish a track of an object. This often requires multiple 

successive position report. 

Probability of Detection The likelihood that an object will be detected within the field of regard. Often derived 

as a ratio of detected targets to the sum of all radar returns. This probability will 

change given the range from the sensor and geometry of the encounter. 

Update Rate The rate at which a sensor will provide updates as to the position and time of 

detection of the objects within the field of regard. 

Transmission Delay Transmission time delay associated with transmitting data packet information from a 

source to a destination 

Packet Loss Ratio Packet Delivery/Reception Ratio: ratio of data-packets-sent to data-packets-received 

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Threat Tracking and Alert 

Target Track Capacity The number of objects that can be simultaneously tracked 

Probability of Lost Tracks The probability of a track losing consistent position returns and becoming stale 

False Alarm Rate An erroneous object detection decision caused by noise or other interfering signals 

exceeding the detection threshold 

Frequency of Strengthening Alerts Frequency of alert commanding increased maneuver magnitude 

Frequency of Weakening Alerts Frequency of alert commanding decreasing maneuver magnitude 

Frequency of Reversal Alerts Frequency of alert commanding reversal of maneuver direction 

Frequency of Yo-Yo Alerts Frequency of multiple subsequent reversal alerts for a given conflict 

Look ahead Time Temporal parameter used to predict the anticipated actions of aircraft over a time 

horizon 

Expected UAS Response Time The expected time associated with a UA completing a resolution maneuver 

Expected Climb/Descent Rate The rate of climb and descent expected of a UAS performing a vertical resolution 

maneuver 

Expected Turn Rate The rate of course change expected of a UA performing a horizontal resolution 

maneuver 

Expected Time to Hover The time required for a UA to halt forward motion and hover 

Conflict Determination and Resolution 

Conflict Duration Total time from first conflict alert to clear of conflict. 

Horizontal Miss Distance at 

Closest Point of Approach 

The horizontal distance at the point in which the UA and object reached the closest 

possible distance 

Vertical Miss Distance at Closest 

Point of Approach 

The vertical distance at the point in which the UA and object reached the closest 

possible distance 

Total Horizontal Path Deviation The summation of all horizontal relative distances between the current UA position 

and the desired path over the course of the route. 

Total Vertical Path Deviation The summation of all vertical relative distances between the current UA position and 

the desired path over the course of the route. 

Maximum Horizontal Path 

Deviation 

The maximum horizontal distance between the current UA position and the desired 

path over the course of the route. 

Maximum Vertical Path Deviation The maximum vertical distance between the current UA position and the desired path 

over the course of the route. 

Probability of Induced Conflicts The likelihood of a conflict resolution maneuver creating a secondary conflict with 

other objects 

Probability of Near Mid-air 

Collisions 

The likelihood of an object having a near mid-air collision with the UA, given that two 

aircraft are at a relative state. 

Probability of Loss of Separation The likelihood of an object coming within a proximity of the UA, defined by a 

prespecified spatial and/or temporal criteria. 

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In order to determine the effectiveness of a task and objectives for a DAA solution the measures 

of performance in Table 8 establishes quantitative means to assess the value attribute of the DAA 

solution. However, a DAA solution independent of context is not practical to determine whether 

the solution is effective, therefore Table 9 describes measures of suitability, which are measures 

of the DAA solution that demonstrate its ability to be supported in the operational environment. 

Measures of suitability are often more qualitative in nature than quantitative. As many of the 

conflict resolution tasks are dependent on the airspace in which a UA is operating Table 9 

provides some example measures which are common to all environments but does not detail 

measures that may be specific within the context of a specific airspace or operational 

environment. 

Table 9: Measures of suitability for DAA solutions. 

Measure of Suitability Description 

Detection 

Mean time to failure The predicted elapsed time between inherent failures of a DAA solution during nominal operation 

Availability The probability that a system in operational at a given point in time under a set of environmental 

conditions. Availability is dependent on the reliability and maintainability of the system 

Susceptibility to 

Weather 

The ability of the DAA solution being available, and/or reliable under a given environmental 

condition 

Threat Tracking and Alert 

Separation Criteria Spatial and/or temporal definition of required minimum separation between the UA and other 

objects 

Alert Criteria Spatial and/or temporal definition of required minimum separation in which a UA is alerted that 

action is needed to be taken to avoid a potential collision 

Clear of Conflict 

Criteria 

Spatial and/or temporal definition of the release of alert due to a hazardous object 

Saliency of Display 

Information 

The degree to which the information is relevant at the point in time in which it is accessed 

Usability of Display 

Information 

The degree to which the information was interpretable and understandable and met the purpose 

for which it was required 

Usefulness of Display 

Information 

The degree to which the information served the purpose that it was desired to fulfill 

Reliability/Accuracy of 

Display Information 

The degree to which information is available when required and is correct at the point in time at 

which it was reported and is error free 

Appropriateness/Safety 

of Maneuver 

Degree to which a maneuver is suitable & fitting to the problem/ situation and has a desired level 

of safety. 

7.2.10 Collision and Obstacle Avoidance 

Collision Avoidance is a UAS capability where the UAS takes appropriate action to prevent a 

midair collision with an airborne hazard. Typically for manned aircraft the separation volume called 

a near-midair collision (NMAC) is used to establish the minimum conflict avoidance separation 

distance to be maintained between aircraft. A NMAC is defined as an incident associated with 

the operation of an aircraft in which a possibility of collision occurs as a result of proximity of less 

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than 500 feet to another aircraft, or could be more qualitatively reported by a pilot or flight crew 

member as a collision hazard existing between two or more aircraft. Quantification of the NMAC 

has been used in collision avoidance systems, such as the traffic collision avoidance system 

(TCAS) and is defined as when two aircraft come within 100 feet vertically and 500 feet 

horizontally. For UAS conflicts with manned aircraft it is generally accepted that the NMAC is an 

appropriate measure for a collision avoidance capability. However, for UA conflicts with other UA 

it is not unanimously agreed amongst the community that an NMAC is an appropriate measure to 

use as a collision avoidance separation criterion as the NMAC is inherently tied to the loss of life 

from a midair collision (MAC) which is not a direct consequence of a UA to UA collision. For a 

collision avoidance capability, action is expected to be initiated within a relatively short time 

horizon before closest point of approach and is considered the capability that is engaged when 

all other modes of separation have failed. Given the size, weight, power, and cost limitations of 

small UAS it may be necessary that collision avoidance systems leverage similar detection 

technologies as employed by a detect and avoid system, however the objectives of collision 

avoidance are inherently different than that of detect and avoid. As collision avoidance is final 

mitigation to resolve conflicts with airborne hazards its main objective is to maximize the distance 

between the UA and the airborne hazard within the minimal amount of time. Considering this 

objective, performance requirements for sensors should be at high levels of integrity and 

assurance (i.e. robustness) to ensure the effectiveness of the collision avoidance mitigation within 

the detection volume. Future considerations for refined NMAC definitions for conflicts between 

UA should be based on navigation performance to encourage efficient use of the airspace. UA 

navigation performance requirements and subsequent UA to UA NMAC definitions can be 

specified based on likelihood (e.g. density of UA operations) and consequence (e.g. population 

density) of a collision between unmanned aircraft for a given airspace. 

Obstacle Avoidance is a UAS capability that is used to take appropriate action to prevent a 

collision with a static or a “low and slow” dynamic obstacle that is in proximity of the UA. Often 

obstacle avoidance would be used in the take-off and landing phases of flight or during unplanned 

emergency landings and initiate when the vehicle is near the surface of the earth. While described 

as an independent system in this document, the obstacle avoidance capability may share similar 

enabling technologies and sensors as the collision avoidance system to accomplish separation 

from obstacles. However, there is clear distinguishing differences between collision avoidance 

requirements and actions and those of an obstacle avoidance system. Closure rate between the 

hazard and the UA may be the most significant difference, where collision avoidance is designed 

to mitigate airborne hazards moving at higher velocities and obstacle avoidance addresses static 

obstacles and dynamic obstacles moving at slower velocities. Moreover, the actions produced by 

the systems may also yield different results. It may be more advantageous to descend during 

collision avoidance conflict whereas climbing or hovering may be a more appropriate response in 

obstacle avoidance hazards. The main objective of an obstacle avoidance system is to maintain 

a minimum distance between the UA and a terrestrial obstacle. Often this objective is achieved 

by halting forward motion towards the static obstacle and requires high robust sensor 

performance at very close proximity around the UA. Many challenges are posed on the 

interoperability between collision avoidance and obstacle avoidance systems if sensors are 

shared between the given technologies. DAA and collision avoidance systems must account for 

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higher closure rates and require greater sensor range, whereas obstacle avoidance systems must 

perform in highly cluttered environments requiring short sensor range with high update rates. 

Table 10: High-Level Requirements for Collision Avoidance and Obstacle Avoidance Capabilities. 

High Level Requirement Requirement Justification 

A collision avoidance capability must be 

required for BVLOS operations. 

This requirement addresses the residual risk of 

collision hazard in the event of a loss of link event. 

A collision avoidance capability should use a 

minimum separation distance based on 

required navigation performance of an 

airspace. 

This requirement promotes the safe and efficient 

use of airspace. 

A collision avoidance capability must be an 

onboard automated capability. 

This requirement addresses the residual risk of 

collision hazard in the event of a loss of link event. 

A collision avoidance capability must maximize 

the distance between the UA and another 

aircraft within a minimal amount of time. 

This requirement addresses the hazard associated 

with operating an aircraft so close as to create a 

collision hazard (e.g. Part 91.111, Part 107.37). 

An obstacle avoidance capability must be 

required for Operations over People. 

This requirement addresses the residual risk to 

persons or property due to an unplanned or 

emergency landing. 

An obstacle avoidance capability should use a 

minimum separation distance based on 

required navigation performance. 

This requirement promotes the efficient use of 

airspace and the consideration of safety with 

respect to persons and property on the ground. 

An obstacle avoidance capability should use 

different minimum separation distance 

requirements for static and dynamic obstacles. 

This requirement promotes the efficient use of 

airspace and the consideration of safety with 

respect to persons and property on the ground. 

An obstacle avoidance capability must be an 

onboard automated capability. 

This requirement addresses the residual risk of 

collision hazard in the event of a loss of link event. 

An obstacle avoidance capability should have 

an onboard audible alert. 

This requirement promotes indirect mitigations by 

non-participants on the ground by raising situation 

awareness. 

An obstacle avoidance capability shall halt 

forward motion of the UA towards the obstacle 

or re-direct the UA away from the obstacle. 

This requirement addresses the hazard associated 

with operating an aircraft in proximity of structures 

(e.g. Part 91.119, Part 107.351). 

Given that the locus of control for DAA, collision avoidance and obstacle avoidance may overlap, 

future research should consider the interoperability between these systems. Furthermore, given 

the highly dynamic nature of dynamic obstacles in urban environments (e.g. pedestrians at a 

crosswalk), additional research is needed to establish guidelines, best practices, and policies for 

automated safe landing. An automated safe landing capability will require interoperability with 

obstacle avoidance and risk monitoring capabilities. 

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Appendix A: Off Nominal Conditions 

During UAS flight operations there is the potential that a UAS may enter an off-nominal condition 

or encounter another aircraft that is in an off-nominal condition. Since small UAS will not carry 

passengers, the elevation of an off-nominal condition to the declaration of an emergency would 

only occur if there is a credible hazard posed to persons on another aircraft and/or persons on 

the ground. The potential for collision between UAS may also warrant hazard declarations when 

operations are occurring over people and could pose a probable likelihood of causing harm to 

persons on the ground. For the purposes of this document, the following off-nominal conditions 

shall be defined to capture the severity of the event: 

● Urgency - A condition in which aircraft performance has been compromised but can still 

safely land; contingency procedures may need to be enacted and stakeholders may need 

to be notified. 

● Distress - A condition in which aircraft performance has been severely compromised and 

safe landing is no longer certain; contingency procedures are enacted, and impacted 

stakeholders are provided notification and information relevant to maintaining safety of the 

NAS. 

There are many credible hazards, noted in Table 11, which need to be addressed to operate UAS 

safely in the NAS, however this appendix addresses a subset of these critical hazards from the 

lens of conflict management. 

Table 11: Critical hazards for UAS Operations. 

Identifier Hazard Risk Statement 

R01 Excursion from Operation Volume 

R02 Aircraft incursion on UAS Operation Volume 

R03 Loss of Control 

R04 Degradation or Loss of Command, Control, and Communication 

R05 Degraded or Loss of Services and Capabilities 

R06 Degraded or Loss of Navigation 

R07 Degraded or Loss of Surveillance 

R08 Adverse Environmental Conditions 

R09 Loss of Safe Landing Capability 

R010 Loss of Energy 

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R01: Excursion from Operation Volume 

An Operation Volume represents the intent of a UA operating in the airspace and therefore a UAS 

Operator would conduct flight planning to define a flight geography that avoids areas of 

unacceptable air and ground risk. The USS would support an operator by incorporating the 

appropriate spatial and temporal buffering to define the operational volume, and onboard and 

ground-based mitigations would help contain the UA to within the Operation Volume. However, if 

there are failures within this layered mitigation, they pose a potential threat to other aircraft 

operating in a local proximity and/or a potential threat to persons or property on the ground. Each 

off-nominal scenario is different, however often an excursion from an operation volume is caused 

by exogenous atmospheric factors (e.g. turbulence, wind gusts), human error, or a component 

failure on the UAS. 

Figure 14: Scenarios of unmanned aircraft departing flight path and blundering through different operational 

boundaries. 

While there are numerous possibilities of factors that can lead to an off-nominal condition the 

following procedures can serve as guidance for expected actions, reportable events, and data 

logging requirements. The following scenarios are related to excursion from the Flight Geography: 

(1) Momentary excursion and return to the Flight Geography 

(2) Prolonged exposure outside the Flight Geography 

(3) Large excursion that results in a breach of the Conformance Volume and timely return to 

the Flight Geography 

(4) Excursion outside of the Operation Volume 

UAS Operators should be conducting flight planning, incorporating onboard technologies that 

support safe use of the airspace, and designing Flight Geographies such that excursions from 

flight geographies are a rare occurrence. The space between the Flight Geography and the 

Conformance Volume serves as a buffer to allow for these occasional deviations, however it is 

expected that the UAS Operator is employing contingency actions to reduce the severity of the 

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deviations. Large deviations beyond the Conformance Volume, sustain time outside of the Flight 

Geography and/or excursions from the Operation Volume represent a deviation from the intent of 

the operation and are grounds for communication of an off-nominal condition to other 

stakeholders of the airspace. The roles and responsibilities of UAS, UAS Operator and USS are 

anticipated to change as the progression from a nominal state of the aircraft transitions into an 

urgency or distress condition. Table 12 details the roles and responsibilities delineation for the 

USS, UAS Operator, and UAS during deviations from an Operation Volume. These procedures 

assume the persistent command, control, and tracking of the aircraft are maintained during the 

excursion. Procedures associated with the loss of command, control, and communications with 

the UA are addressed elsewhere in this Appendix. 

Table 12: Roles and responsibilities during excursion from Operation Volume. 

USS UAS Operator UAS 

Within Flight 

Geography 

Responsible for monitoring UA 

conformance to Flight 

Geography 

Responsible for: 

• Defining Flight Geography 

and containing UA within 

Flight Geography 

• Ensuring UA Geographic 

Flight Containment 

mitigations are enabled (if 

applicable) 

Responsible for: 

• Enforcing Geographic Flight 

Containment Mitigations (if 

applicable) 

• Displaying Operation Volume to 

UAS Operator 

• Providing alerts and executing 

corrective action if preventative 

or recovery thresholds are 

crossed 

Excursion Responsible for: Responsible for commanding Responsible for executing corrective 

from Flight • Notifying UAS Operator of corrective maneuvering to return maneuvering to return UA to Flight 

Geography Flight Geography breach 

• Logging Event Data as 

Noncompliance Event 

UA to Flight Geography, and/or 

modifying the Flight Geography to 

maintain ACTIVE operation state 

Geography 

Breach of 

Conformance 

Volume 

Responsible for: 

• Notifying UAS Operator of 

Conformance Volume 

breach 

• Declaring NONCONFORMING operation 

to USS Network 

• Declaring an operation 

ROGUE to the UAS 

Operator and USS Network 

when the UA has multiple 

successive breaches of the 

Conformance Volume 

• Logging Event Data as Offnominal Event by soliciting 

an Off-nominal Report from 

the UAS Operator 

Responsible for: 

• Commanding corrective 

maneuvering to return UA to 

Flight Geography, and/or 

modifying the Flight 

Geography to maintain 

ACTIVE operation state 

• Completing an Off-nominal 

Report upon the completion 

of the operation 

Responsible for executing corrective 

maneuvering to return UA to Flight 

Geography 

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Prolonged 

exposure 

outside of 

Flight 

Geography 

Responsible for: 

• Notifying UAS Operator of 

Time-to-Violation prior to 

NON-CONFORMING 

operation declaration 

• Notifying UAS Operator of 

Time-to-Violation prior to 

ROGUE operation 

declaration 

• Declaring NONCONFORMING or ROGUE 

operation to USS Network, 

based on the duration of 

exposure outside the Flight 

Geography 

• Share position information 

of UA with USS Network 

• Logging Event Data as Offnominal Event by soliciting 

an Off-nominal Report from 

the UAS Operator 

Responsible for: 

• Commanding corrective 

maneuvering to return UA to 

Flight Geography, and/or 

modifying the Flight 

Geography to maintain 

ACTIVE operation state 

• Notifying USS if unable to 

provide corrective maneuver 

or UA is unable to execute 

corrective maneuver by 

declaring a state of 

URGENCY or DISTRESS 

and ABORTING the 

operation 

• Update vehicle-to-vehicle 

status message to reflect 

off-nominal condition (if 

applicable) 

• Completing an Off-nominal 

Report upon the completion 

of the operation 

Responsible for: 

• Executing corrective 

maneuvering to return UA to 

Flight Geography 

• Providing vehicle health status, 

command and control link status, 

and telemetry to the UAS 

Operator to determine whether 

execution of corrective 

maneuver is achievable. 

Return to 

Flight 

Geography 

Responsible for declaring the 

return of the UA to an ACTIVE 

operation to the UAS Operator 

and the USS Network 

Responsible for: 

• Verifying remaining UA flight 

path is contained within 

Flight Geography 

• Ensuring UA Geographic 

Flight Containment 

mitigations are re-enabled (if 

applicable) 

Responsible for: 

• Enforcing Geographic Flight 

Containment Mitigations (if 

applicable) 

• Displaying Operation Volume to 

Operator, and 

• Providing alerts and executing 

corrective action if preventative 

or recovery thresholds are 

crossed 

Excursion 

from 

Operation 

Volume 

Responsible for: 

• Notifying UAS Operator of 

Operation Volume breach 

• Declaring ROGUE 

operation to USS Network 

• Share position information 

of UA with USS Network 

• Logging Event Data as Offnominal Event by soliciting 

an Off-nominal Report from 

the UAS Operator 

• Declaring URGENCY or 

DISTRESS condition to 

FIMS (to disseminate to the 

relevant air traffic facilities) 

if UA poses a credible 

hazard to nearby manned 

aircraft operations 

• Providing any relevant data 

to FIMS 

• Increase USS service area 

to capture expected flight 

path (as applicable) 

Responsible for: 

• Initiating safe landing 

procedures to route UA to 

the nearest location suitable 

for a safe landing 

• Notify USS of intended flight 

path while ABORTING 

OPERATION, to ensure 

awareness of other 

operations impacted by the 

change 

• Update vehicle-to-vehicle 

status message to reflect 

off-nominal condition (if 

applicable) 

• Completing an Off-nominal 

Report upon the completion 

of the operation 

Responsible for: 

• Executing Safe Landing 

Procedure 

• displaying any revisions to 

Operation Volume to UAS 

Operator 

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The Log Event Data is a set of data that is requested from a UAS Operator and/or USS, recorded 

for time histories over the course of the event, and made available upon request by appropriate 

governmental agencies (e.g. FAA, NTSB). 

As part of the Performance Authorization process, a UAS Operator will get approval for an Area 

of Operation in which the measures to ensure safety of the operation have been deemed 

appropriate given the Operators safety mitigations. Based on the design of the Area of 

Operations, the air risk and/or ground risk outside of this Approved Area of Operations could 

potentially be unacceptably high given the safety mitigations employed by the UAS Operator. A 

breach of the approved Area of Operation may constitute communication between a USS and 

relevant air traffic facilities through FIMS when operations are conducted adjacent to controlled 

airspace if a credible hazard exists. 

R02: Incursion of Intruding Aircraft into the Operation Volume 

Operation Volumes are constructs that aid a UAS Operator in ensuring that their UA does not 

breach airspace with flight restriction and reduces the likelihood of airborne conflicts with other 

UA in the airspace. While operation volumes can be issued as notices of intent to operate to 

other aircraft in the airspace, via a notification service, they do not constitute as “reservations” or 

exclusive rights to airspace use over a duration of time. Therefore, a manned aircraft, who is not 

participating in UTM, is within their rights to use airspace that has been published to UTM as a 

UAS Operation Volume. This inherent fact underlines the need for clarity on right of way rules, 

such as those established under 14 CFR Part 91.113, 14 CFR Part 91.111, and 14 CFR Part 

107.37. While “well clear” definitions are currently in development (e.g. Science and Research 

Panel recommended well clear definition between sUAS and manned aircraft), it should be 

considered that the context of each airspace may warrant different application of separation 

requirements. Current discussions have explored the concept of UA to manned aircraft separation 

employing a dualistic separation by airspace structure (i.e. expected manned aircraft routes and 

traffic patterns) and separation by a “well clear” standard to reduce the burden on UAS Operators 

to deploy large size, weight, power, and cost equipment, and design complicated onboard 

automation capabilities to enter complex airspace that already benefits from air traffic control and 

airspace structure. This dualistic separation approach would be applied by UAS Operators 

defining an Operation Volume a sufficient separation from a known airspace structure and 

monitoring manned aircraft that fly within that structure. If manned aircraft are flying within the 

bounds of their airspace structure and the UA are contained within the bounds of their Operation 

Volume then safe separation has been achieved, even in the distance between the airspace 

structure and the Operation Volume is smaller than a “well clear” separation definition. If either 

the manned aircraft or the UA have deviated from their expected airspace structure/Operation 

Volume, then separation requirements are dictated by the “well clear” definition. This approach 

has inherent draw-backs in that it relies on the assumption that a characterization of where 

manned aircraft operate in a given airspace has been conducted to derive the expected airspace 

structures and the use of surveillance of manned aircraft that capture the status of aircraft within 

those structures is available. Service Suppliers that offer a surveillance service could satisfy these 

assumptions to provide the benefits of smaller separation requirements to the UAS Operator. In 

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the absence of this dualistic construct the more conservative “well clear” definition would apply 

for each operator to comply with and diligence is required by the UAS Operator to design their 

Flight Geography in such a way that it would not inherently trigger false alarms for a DAA system 

around known traffic patterns. 

Figure 15: Depiction of boundaries considered for the incursion of an intruding aircraft. 

As an operator determines the mitigations employed to address conflict management within the 

airspace they wish to fly, an understanding of how the interplay between the mitigations is 

warranted. Figure 15 depicts the surveillance volume provided by a surveillance service or ground 

surveillance capability, the Operation Volume defined by the UAS Operator, and the detection 

volume defined by the performance of a detect and avoid and/or collision avoidance capability. 

For a conflict mitigation strategy that employs both services and capabilities the following 

requirements should be considered 

• An Operation Volume should consider the detection volume in its definition to reduce false 

alerts 

• An Operational Volume must be wholly defined within the boundaries of the surveillance 

volume to reduce missed alerts 

• A detection volume must be wholly contained within the boundaries of the surveillance 

volume across the entirety of the flight path to reduce popup alerts 

Inconsistencies in situation awareness, alerting, and corrective actions may be caused if care is 

not taken by the Operator in ensuring that the surveillance volume properly supports their 

operation and the definition of the Operation volume and required performance of the detection 

volume are not appropriately defined. 

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Table 13: Roles and responsibilities during intruder incursion on Operation Volume. 

USS Surveillance Services 

and Capabilities4

UAS Operator UAS 

Manned 

Aircraft 

within 

Surveillance 

Volume (i.e. 

surveillance 

service) 

Responsible for: 

• Notify USS 

Network of any 

operations 

modifications 

to the 

Operation 

Volume 

Responsible for: 

• Making position 

reports available for 

all intruding 

manned aircraft in 

the Surveillance 

Volume 

• Tracking intruder 

aircraft and 

providing updates 

to known position, 

heading, speed, 

etc. 

• (Optional) Providing 

alerts to UAS 

Operator / UAS of 

intruder aircraft 

detected within 

close proximity of 

UAS Operation 

Volume or UA 

Responsible for: 

• Displaying current 

position of UA and 

nearby intruder aircraft 

on the same display 

• Track intruder manned 

aircraft and UA aircraft 

to determine the threat 

of the intruder to the 

operation 

• Notify USS of any 

Operation Volume 

modifications, as a 

pre-emptive action 

taken to avoid a 

potential conflict 

Responsible for: 

• Providing current UA 

position and operation 

information 

Manned 

Aircraft 

within 

Detection 

Volume (i.e. 

detect and 

avoid 

capability) 

Responsible for: 

• Monitoring relative 

position and closure 

rates between UA and 

intruder 

• Determine if corrective 

action in needed 

based on DAA alerting 

and separation 

requirements (e.g. 

well-clear) 

• Notify USS of any 

Operation Volume 

modifications, taken to 

avoid a potential well 

clear violation 

Responsible for: 

• Detect and track 

intruder through DAA 

capability 

• Providing DAA 

alerting to UAS 

Operator for 

determination of 

corrective action 

• Executing Corrective 

Action to resolve 

conflict 

• Monitoring conflict 

with intruder and 

providing a clear of 

conflict notification to 

the UAS operator 

Manned 

Aircraft 

breaches 

Flight 

Volume 

Manned 

Aircraft in 

close 

proximity (i.e. 

collision 

avoidance 

capability) 

Responsible for: 

• Notify USS of any 

Operation Volume 

modifications, 

taken to avoid a 

potential near 

midair collision 

(NMAC) 

• Completing an 

Off-nominal 

Report upon the 

completion of the 

operation 

Responsible for: 

• Detect and track 

intruder through 

collision avoidance 

capability 

• Notify UAS Operator 

of collision threat 

• Determine and 

execute corrective 

action to avoid a 

NMAC 

• Notify UAS Operator 

of collision 

4 Surveillance Services may be provided through a USS or directly to the UAS Operator/UAS as a 

supplemental data service provider. Surveillance Capabilities could be provided by ground surveillance as 

described in Section 7.2.8. 

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•

avoidance corrective 

action initiation 

Monitoring conflict 

with intruder and 

providing a clear of 

conflict notification to 

the UAS operator 

R03: Loss of Control 

For the purposes of this document, a loss of control will be defined as a loss of predictable 

behavior of the UA. Common causes of a loss of control may be a vehicle malfunction resulting 

in a “fly away”, intentional or unintentional interference with the command and control capabilities 

of the aircraft by third parties (e.g. cyber-attack), or adverse atmospheric conditions resulting in 

the aircraft exhibiting unpredictable behavior. One of the challenges for the UAS Operator is 

ensuring that they have a sufficient awareness of their locus of control of the vehicles behavior 

and identifying when unexpected behavior is occurring. Common ways operators may accomplish 

this monitoring is through direct means such as tracking the UA along its flight path, observing 

responsiveness of the execution of command maneuvers and the observation of health 

monitoring systems onboard the vehicle. Indirect means may also be employed to support UAS 

Operators, such as observation of their aircraft by other UAS Operators though remote 

identification, vehicle-to-vehicle communication or UAS reports (UREP) or distress broadcasts 

from the UA as observed by other ground systems. The loss of control is a hazardous condition 

for UAS and should be declared immediately by a UAS Operator once the state is identified. Loss 

of control constitutes an urgency or distress condition given the environment in which the UA is 

being operated and notice should be provided from a UAS Operator to a USS and subsequently 

to impacted ATC facilities through FIMS (when applicable). Table 14 details the roles and 

responsibilities associated with an UA loss of control. 

Table 14: Roles and responsibilities during a loss of UA control. 

ATC USS UAS Operator UAS 

Excursion 

from 

Operation 

Volume due 

to Loss of 

Control 

None Responsible for: 

• Notifying UAS 

Operator of Operation 

Volume breach 

• Declaring ROGUE 

operation to USS 

Network 

• Share position 

information of UA with 

USS Network 

• Logging Event Data as 

Off-nominal Event by 

soliciting an Offnominal Report from 

the UAS Operator 

Responsible for: 

• Initiating safe landing 

procedures to route UA 

to the nearest location 

suitable for a safe 

landing 

• Notify USS of intended 

flight path while 

ABORTING 

OPERATION, to ensure 

awareness of other 

operations impacted by 

the change 

• Update vehicle-tovehicle status message 

to reflect off-nominal 

condition (if applicable) 

Responsible for: 

• Executing Safe 

Landing Procedure 

• displaying any 

revisions to 

Operation Volume to 

UAS Operator 

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• Completing an Offnominal Report upon 

the completion of the 

operation 

Incursion 

into nonapproved 

controlled 

airspace 

due to Loss 

of Control 

Responsible for: 

• Request relevant 

information from 

FIMS to 

determine 

impact on 

manned 

operations 

• Initiating 

airspace controls 

and actions to 

ensure aircraft 

under ATC 

services are 

separated from 

the UA under 

URGENCY or 

DISTRESS 

condition 

Responsible for: 

• Determining whether 

UA poses a credible 

hazard to manned 

aircraft 

• Declaring URGENCY 

or DISTRESS 

condition to FIMS (to 

disseminate to the 

relevant air traffic 

facilities) if UA poses a 

credible hazard to 

nearby manned aircraft 

operations 

• Providing any relevant 

tracking and operation 

data to FIMS 

• Increase USS service 

area to capture 

expected flight path (as 

applicable) 

Responsible for: 

• Provide relevant UAS 

and operations 

information to USS to 

support USS or FIMS 

contingency 

management 

mitigations 

Responsible for: 

• Executing 

Automated Detect 

and Avoid and/or 

collision avoidance 

Functions to not 

pose a collision 

hazard to manned 

aircraft 

• Executing 

Automated Safe 

Landing Procedure 

based on 

communication 

timeout 

• displaying any 

revisions to 

Operation Volume to 

UAS Operator (if 

possible) 

To ensure the safety of the airspace, it is the responsibility of all UAS operators to support efforts 

to safely address instances of a loss of control. To this end the following would be required of all 

UAS Operators receiving services from a USS: 

● A UAS Operator flying beyond visual line of sight MUST be connected to the Flight 

Information Management System (FIMS) through a UAS Service Supplier function 

● A UA in vehicle-to-vehicle communication with a UA in distress MUST report that 

encounter to the UAS Operator who relays that information to their subsequent USS and 

that information is shared with the local USS Network. 

● The “right of way” of unmanned aircraft MUST be provided to the UA under a known 

urgency or distress condition. 

The Log Event Data is a set of data that is requested from a UAS Operator, recorded for time 

histories over the course of the event, made available to other entities impacted by the event. The 

following table details some of the data logging requirements for loss of control event. 

Last Known Information Format V2V UAS Operator 

to USS 

USS to Other 

Impacted Operators 

USS to FIMS (if 

required) 

GUFI [text] X X X X 

Latitude [float] X X X X 

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Longitude [float] X X X X 

Altitude [WGS84] [float] X X X X 

Course [float] X X X X 

Ground Speed [float] X X X X 

Remaining Endurance [float] X X 

C2 Data Link Status [Boolean] X X 

Navigation Integrity Status [Boolean] X X 

Control of UA [Boolean] X X 

Priority Message [text] X X X 

R04: Loss or Degradation of Command, Control, and Communication 

The procedures and requirements associated with loss or degradation of the command and 

control link are the primary topic of discussion in the Communication and Navigation Working 

Group within the RTT, however this document considers the implications of this condition on 

ensuring separation. Table 15 describes different derived requirements to be considered to 

address the collision hazard condition under a loss of command, control, and communication. 

Table 15: Communication Contingency Management Requirements5. 

Re. ID Requirement Text Requirement Justification 

OSM.001 The operator MUST have the means to 

detect loss of communication between 

aircraft and its operator. 

The UTM system is built for operators to perform missions within constraints 

and directives that can change over time. Therefore, operators must know 

whether they can communicate or not with their UA to adhere to dynamic 

constraints and directives. 

OSM.002 The operator SHOULD make the 

means to detect loss of communication 

with aircraft known to USS. 

USS, with appropriate data from Supplemental Data Service Provider 

(SDSP), should be able to provide communications quality of service 

information for a mission when the means to detect loss of communication is 

known. This will likely reduce the loss of communication incidence during a 

mission. 

OSM.003 The operator MUST define steps to 

mitigate the loss of communication with 

aircraft. 

Operators must communicate with their UA to adhere to constraints and 

directives, which can change during a mission. Therefore, mitigation steps 

must be in place to resolve the loss of communication safely. 

OSM.004 The operator SHOULD make the steps 

to mitigate the loss of communication 

with aircraft known to USS. 

USS, with similar information from other operators and adjacent USSs, 

should be able to support mitigation steps with minimal impact on overall 

operations under its service. 

A loss of command and control does not inherently indicate that an operation must be aborted. 

For a UA that has onboard autonomous mission capabilities and detect and avoid capabilities, 

BVLOS operations may continue the operation by providing notice to other airspace users of a 

5 Jung, J., & Nag, S. (2020). Automated Management of Small Unmanned Aircraft System Communications 

and Navigation Contingency. In AIAA Scitech 2020 Forum (p. 2195). 

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degraded state and utilizing the advance onboard technology to navigate and separate from other 

aircraft. Furthermore, operations over people may also continue with a sufficient autonomous safe 

landing capability. If these advance capabilities do not exist, a more conservative approach must 

be taken to ensure safety. Another means of regaining control of the operation is for a UA to have 

redundancy in the C2 links to reduce the likelihood of a loss of C2. In the event of a loss of C2 a 

UA may opt to execute procedure to regain the C2 link, this procedure must be communicated 

with the USS and any relevant changes to the Operation Volume to execute the procedure must 

be input immediately. The USS shall change the operation state to non-conforming to notify 

nearby operators of a reduced UAS Operator capability and a loss of USS tracking. Furthermore, 

upon a loss of C2 the UA shall update the V2V message to represent the change in controllability 

state and other UAs receiving this update via V2V communication shall submit a UREP to notify 

the USS network of the whereabouts of the UA under loss of C2 condition. 

Table 16: UAS and Operator navigation requirements under loss of communication operating condition. 

Hazard Condition Derived Conflict Management Requirements 

Collision hazard under 

loss of communication 

UA shall assume authority to execute collision avoidance maneuvers during a loss of communication. 

UAS Operator shall define alternative landing location which are known to the UA and USS as part of 

their flight planning. 

UAS shall display link quality of service to the UAS Operator via an airspace display interface. 

Under a loss of communication condition, the UAS Operator shall provide necessary partial and/or 

temporal updates to the Operational Volume to be consistent with the contingency mitigation steps 

Under a loss of communication condition, the UAS Operator shall monitor surveillance services, 

surveillance capabilities, and UREP reports to validate conformance to UA contingency mitigation 

Under a loss of communication condition, UA shall share information regarding degraded 

communication capability via the vehicle to vehicle communication 

If the C2 link cannot be regained after a duration of time the UA shall initiate a safe landing 

sequence at a pre-designated alternate landing location. The UAS Operator shall be monitoring 

the expected procedure and time associated with the contingency mitigation plan and close the 

Operation Volume after the contingency plan is expected to complete. During the loss of link and 

subsequent contingency plan, the UAS Operator shall be monitoring any available surveillance 

feeds, including UREPs, to identify any deviations from the expected contingency plan. If a 

deviation is observed the UAS Operator must immediately declare an emergency to their 

respective USS and provide the last known information regarding the flight. The loss of C2 

process is depicted in Figure 1. 

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Figure 16: High-level Loss of C2 Communications Mitigations6. 

R05: Loss or Degradation of UAS Services 

Service that support a UAS operation will be utilized by a UAS Operator to ensure safety, security, 

mission success, efficient use of the airspace and equitable access to the airspace. Not all 

services will be considered critical for the safety of operations, however those that are critical to 

operations pose challenges to UAS Operators when the integrity or availability of those services 

are in question. In the conflict mitigation model, the services that result in harm can be categorized 

as follows: 

● Degraded supplemental data services that are inherent to the conflict mitigation 

strategy of a single operator. An example is the loss of connection of UAS Operator with 

a Surveillance Service provided by a SDSP. 

● Degraded shared services that are inherent to the conflict mitigation strategy that was 

utilized amongst many UAS Operators. An example is the loss of performance of a Conflict 

Advisories and Alert Service provided by a USS that supported a large UAS Operator 

subscription based in a geographic area. 

● Degraded Service Provider who provides a set of services that are inherent to conflict 

mitigation strategies for a UAS Operator subscription base in a geographic area. An 

example is the loss of a surveillance data feed that degrades the performance of Conflict 

Advisory and Alert Services, Flight Planning Services, and Dynamic Re-routing Services 

or a loss of all services provided by a USS. 

● Degradation of the Flight Information Management System which is a requirement for 

UAS Operators to connect to if conducting BVLOS operations in order to receive 

communications, directives, and information regarding the state of the airspace from the 

ANSP. 

J. Jung, S. Nag, H. C. Modi, “Effectiveness of Redundant Communications Systems in Maintaining 

Operational Control of Small Unmanned Aircraft,” 38tth DASC 2019, San Diego, CA, September 8-12, 

2019., in press. 

6

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To ensure the safety of the airspace, it is the responsibility of all UAS operators, USS and SDSP 

providers to support efforts to safely address instances of a loss of UAS services. To this end the 

following would be required of each of the stakeholders: 

● A UAS Service Supplier MUST monitor the integrity, availability, and security of the 

services they provide. 

● A Supplemental Data Service Provider MUST monitor the integrity, availability, and 

security of the services they provide. 

● A USS and/or SDSP supporting a UAS Operator MUST provide the health status 

information of their services AND notify UAS Operators if the performance of their service 

has degraded below a range specified in their service agreement 

● A UAS Operator MUST monitor the availability of the connection to the services providers 

they are utilizing to support their operation 

● A UAS Operator MUST monitor the integrity and performance of the services supporting 

their operations to ensure that they are following their performance authorization 

The determination of the phase and severity of emergencies due to a loss of UAS services is 

circumstantial and could yield an infinite variety of possible emergency situations therefore 

specific procedures can heuristically be described but would be on a service by service basis. 

However, a basic process can be followed in the absence of more explicit procedures established 

by the service providers. 

● Upon a loss of degradation of a service the UAS Operator attempts to regain the service 

or waits a pre-specified amount of time for the service provider to regain the service before 

continuing with their mission 

● If the service is unable to be restored then UAS Operator aborts their operation, updates 

their route to the nearest pre-specified alternate landing location, updates their Operation 

Volume (if possible), and commands a landing sequence once they have arrived at their 

alternate land location. It should be noted that during this transition, UAS tactical 

separation mitigations and available USS services are used to ensure conflict resolutions 

while en-route to the alternate landing location. 

● If a loss of FIMS is encountered the UAS Operator has a duration of time prespecified by 

the ANSP before initiating any mission abort actions, as FIMS is not critical to ensuring 

separation between aircraft. However, without connecting to FIMS a UAS Operator has 

lost the ability to receive communications from the ANSP with regards to the accessibility 

and state of the airspace. 

R06: Loss or Degradation of Navigation 

Table 17: Navigation Contingency Management Requirements7. 

Re. ID Requirement Text Requirement Justification 

OSM.005 The operator MUST have the means to 

detect loss of aircraft onboard 

navigation. 

The UTM system is built for operators to perform missions within constraints 

and directives. Therefore, when UA is not maintaining the necessary 

navigation solution accuracy and integrity to adhere to constraints and 

directives, the operator must know this condition. 

7 Jung, J., & Nag, S. (2020). Automated Management of Small Unmanned Aircraft System Communications 

and Navigation Contingency. In AIAA Scitech 2020 Forum (p. 2195). 

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OSM.006 The operator SHOULD make the 

means to detect loss of aircraft onboard 

navigation known to USS. 

USS, with appropriate data from SDSP, should be able to provide navigation 

service quality forecast for UAS mission when its means to detect loss of 

navigation is known. This will likely reduce the loss of navigation incidence 

during a mission. 

OSM.007 The operator MUST define steps to 

mitigate the loss of aircraft onboard 

navigation. 

UA must maintain the necessary navigation solution accuracy and integrity 

to adhere to constraints and directives. Therefore, mitigation steps must be 

in place to resolve the loss of navigation safely. 

OSM.008 The operator SHOULD make the steps 

to mitigate the loss of aircraft onboard 

navigation known to USS. 

USS, with similar information from other operators and adjacent USSs, 

should be able to support mitigation steps with minimal impact on overall 

operations under its service. 

OSM.009 The operator MUST collect off-nominal 

situation data. 

When UTM operations encounter off-nominal situations, data must be 

collected to take lessons learned to reinforce operational compliance and to 

enhance operational safety. 

The procedures and requirements associated with loss or degradation of the command are not 

explicitly covered in this document however considerations of the implications of this condition on 

ensuring separation are explored. Table 18 describes different derived requirements to be 

considered to address the collision hazard condition under a loss of navigation. 

Table 18: UAS and Operator navigation requirements under loss of navigation operating condition. 

Hazard Condition Derived Conflict Management Requirements 

Collision hazard under 

loss of navigation 

UA shall assume authority to execute collision avoidance and obstacle avoidance maneuvers until a UA 

is on the ground 

UAS Operator shall define alternative landing location which are known to the UA and USS as part of 

their flight planning 

UAS shall display navigation quality of service to the UAS Operator via an airspace display interface 

Under a loss of navigation condition, the UAS Operator shall provide necessary partial and/or temporal 

updates to the Operational Volume to be consistent with the contingency mitigation steps 

Under a loss of navigation condition, the UAS Operator shall declare an emergency to the USS 

Under a loss of navigation condition, UA shall share information regarding loss of navigation capability 

via the vehicle to vehicle communication 

The navigation function is a critical enabler of BVLOS, operations over people, and can 

fundamental to supporting many onboard separation technologies. In environments in which the 

UA is flying over areas with low ground risk and even low air risk the required performance of the 

navigation capabilities might be minimal for BVLOS operations; such as only requiring a UA to 

have a global navigation solution. Whereas operations over people heighten the navigation 

requirement to include both a global and local navigation solution and a safe landing capability. 

Furthermore, to support separation, a collision avoidance and obstacle avoidance capability 

would need to be onboard the UA. In the event of a loss of navigation condition, where the global 

navigation source is lost, if the local navigation source is available the operation can continue 

while the quality service of the local navigation source is maintained. A navigation quality of 

service degradation alert will be displayed to the UAS Operator and the UA will attempt to regain 

the global navigation source to continue the full operation. If the global navigation source is not 

regained or the local navigation source becomes unavailable, then UA would initiate a safe 

landing sequence. The UAS Operator will modify the Operation Volume to communicate the safe 

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landing sequence to the USS, declare an emergency to the USS as the UA tracking will no longer 

be available/reliable. If equipped with a V2V communication capability, the UA will notify other UA 

in the vicinity of an emergency state due to loss of navigation. Other UAs receiving this update 

via V2V communication shall submit a UREP to notify the USS network of the whereabouts of the 

UA under loss of navigation condition. The UAS Operator shall send all required off-nominal 

information regarding the loss of navigation to the USS as required. 

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