Airborne Collision Risk Classification

Introduction

The continuing integration of unmanned aerial system operations into the National Airspace System requires new or updated regulations, policies, and technologies to enable safe and efficient use of the airspace. Detect and Avoid (DAA) systems utilized by UASs are one such technology that is actively being standardized. To mitigate the risk of midair collisions, these systems consists a functions to sense and identify potential hazardous encounters with other aircraft and then recommend a maneuver such that the UAS avoids the other aircraft.

One standardization effort to define DAA system performance requirement is led by the ASTM Committee F38 on Unmanned Aircraft Systems, Subcommittee F38.01 on Airworthiness. This subcommittee established working group 62668 with the objective to define minimum performance standards for DAA systems applicable to smaller UAS BLVOS operations for the protection of manned aircraft in lower altitude airspace. Smaller UASs are defined in the ASTM standard as having a wingspan or equivalent of 25 feet or less.

This ASTM performance standard prescribes different requirements, such as those for DAA system availability or assurance, based on generalized airborne collision risk classifications for specific operating locations. In response, this software was developed to quantitatively classify and visualize the ASTM-based airborne collision risk classifications for specific locations. The software was not developed to identify the risk a UAS colliding with the ground or third party non-participants. Additionally while the software developers are not a civil aviation authority or air navigation service provider, this software may be used as part of a determination of the initial airborne collision risk classification. This initial determination aligns with many of the concepts described in the JARUS 2019 SORA 2.0.

Airborne Collision Risk Classifications

The ASTM F38 WK62668 DAA performance standard discusses generalized airborne collision risk classifications. These risk classifications were derived from guidance developed by the JARUS 2019 SORA 2.0. It is important to note that these generalized Airborne Collision Risk Classifications were created with mainly cooperative intruders in mind. Care should be taken when using these generalized classifications to describe collision risk with non-cooperative intruders.

While the ASTM standard does not prescribe a set of requirements for each classification nor specify a method to determine air risk, it provides generalized guidance on the context for each risk classification. Given this mostly quantitative guidance, this software use open source datasets to identify and visualize air risk classes given specific latitude, longitude, and altitude positions.

For our definitions, we assume rural areas have a population density of 100 people per square mile or less. While rural areas have not been formally defined by the FAA or for SESAR U-Space, we initially defined rural areas for low risk airspace DAA as having a population density of 100 or less. This quantitative criteria for rural areas was based on the draft D&R MOC from February 2020 or FAA brief to type certificate applicants from July 2019.

As with any generalization, when the area becomes more refined there will be specific areas where the generalized classification levels will be true, and other specific areas where the generalized classification levels will not be true. Care should be taken when using these generalized classifications to describe collision risk with non-cooperative manned aircraft since these classifications were created with primarily cooperative manned aircraft in mind. For specific operations, the UAS operator should work with the local airspace authority to ensure that the appropriate air risk classification is assigned to the operational volume. Furthermore, the software does not estimate nor make assumptions about the likelihood of a UAS encounter a cooperative transponder-equipped or noncooperative manned aircraft. In coordination with the local airspace authority, tt is possible that for a given location, the airborne risk classification could differ for cooperative transponder-equipped and noncooperative manned aircraft.

Specifically, we defined the default risk criteria, within the United States, as the following:

Low Air Risk

Uncontrolled airspace

Below 500 feet AGL

Over a rural area (100 people per square mile or less, within a US census block group)

At least 5 nautical miles away from aerodromes

Medium Air Risk

Uncontrolled airspace (no altitude ceiling)

Below 500 feet AGL in controlled airspace (Class B, C, D)

At least 5 nautical miles away from the center point of Class B, C, and D aerodromes

Below 500 feet AGL over an urban area (greater than 100 people per square mile, within a US census block group)

Below 500 feet AGL in Class E or G aerodromes

High Air Risk

If a location fails to satisfy all the low or medium risk criteria, it is classified as high risk. We assume that these locations are where manned cooperative transponder-equipped aircraft predominately fly and/or where a smaller UAS would frequently encounter cooperative transponder-equipped manned aircraft. Elevation for a given location(latitude, longitude) is obtained by The National Map Elevation Point Query Service (EPQS). If the query does not return a result for the elevation, the AGL altitude can not be calculated. In this event, the location is assigned high air risk by default.

Extremely Low Air Risk

We do not quantitatively define or identify locations where manned aircraft manned aircraft predominately do not fly and/or were it is extremely improbable for a smaller UAS to encounter any manned aircraft.