Unmanned Aircraft Systems Risk Assessment

ABSTRACT

This paper outlines a review of the relevant civil and military regulation applicable to Unmanned Aircraft Systems (UAS) and establishes a comparison between current relevant UAS risk assessment frameworks, viz., JARUS SORA, FAA Risk Index, EDA Risk Assessment Tool (RAT). Furthermore, this research presents a thorough, yet innovative, methodology for the assessment of risk in the operation of UAS with the goal of assisting the decision-making process of airworthiness authorities in the issuance of permits to fly, the pRAT. It is concluded that SORA is the most holistic methodology, due to the consideration of ground and air risk, added to the consideration of energy and UAS specific characteristics; despite simpler, the FAA order focuses on risk categories associated with UAS and operation location characteristics, still presenting an elevated potential for standardization; the pRAT approach builds on the RAT and focuses in obtaining answers of a design integrity checklist specially programmed to provide clear insight on the design safety of the UAS, however, lacks on the lack of human factors and air risk class. . The RAT was found to have a profound analysis of the design integrity of the UAS, however, it lacks on means of compliance, operational aspects and air risk classification.

INTRODUCTION

Although inspired on manned aircraft operations, the operation of Unmanned Aircraft Systems (UAS) differs from the former in various aspects, from which the airworthiness certification requirements take a predominant position. Airworthiness certification is carried out to assure an acceptable level of safety of an aircraft. While, for manned aircraft, such safety levels are commonly accepted, for their unmanned counterparts there is still not a consensus, namely for smaller size UAS. Currently, a manned aircraft must be certified as airworthy according to existing airworthiness specifications in order to operate. The existing UAS airworthiness specifications are STANAG 4702, STANAG 4703, and STANAG 4671, which tend to not be used by the relevant stakeholders due to the level of demand required. In addition, MIL-HBK-516 comprises the Airworthiness Certification Criteria, including criteria for UAS. Conversely, the airworthiness certification of UAS typically uses a different approach which is dependent on the risk that it poses to ground and third parties.

If, on the one hand, certification requirements of UAS were developed and standardized to ensure that an acceptable level of safety of UAS is achieved; on the other hand, there is evidence that suggests the non-adoption of such requirements as these are considered too onerous for the development and lifecycle support of a small UAS. Bearing in mind that small UAS – up to 150kg of Maximum Take-off Weight (MTOW) – are responsible for the greater percentage of uses in UAS operations and that these systems typically have a reduced applicability scope and lifecycle, it becomes evident that the compliance of the existing UAS certification specifications become too demanding for majority systems.

As a result, several international agencies have collaborated in the development of frameworks that aimed at circumventing the need for airworthiness certification of UAS, while still guaranteeing the required level of safety of the systems. These frameworks are based on the assessment of the risk that is inherent to the operation of a specific UAS, by an operator, in a designated location in time.

Despite a similar interpretation of the needs, the risk assessment frameworks that have been developed thus far have focused on different aspects of the operation for the assessment of the risk of operating a UAS. While some focus on the integrity of the UAS, with only a little consideration on the operational aspects of the mission; others focus on the standard operation scenario, risk mitigation or tactical strategies, operational safety objectives, and operational limitations for that specific scenario. Such aspects make it difficult to develop and agree on a specific framework suitable for risk assessment, as well as to an approach for the harmonization among regulatory and airworthiness authorities.

Due to the UAS market growth, small UAS are used both by military and civil operators. This dual-use characteristic contributes to a reduction of the cost of the UAS for the military, given the need for reduced-cost civil UAS operations. Therefore, the military community should act and determine how to assess such UAS and, consequently, issue permits to fly under specific requirements, since airworthiness certification of such platforms is far too demanding for UAS which are intended to be used in specific scenarios, for considerably small time periods.

The research methodology employed in the present work relies mainly on a thorough literature review. This article compares the advantages and drawbacks of several risk assessment frameworks for UAS, which include JARUS’s Specific Operations Risk Assessment (SORA), FAA Order 8130.34D (Risk Index), and European Defence Agency (EDA) Risk Assessment Tool (RAT). Furthermore, the research presented brings a novel tool for the risk assessment of UAS, developed with the goal of aiding in the assessment of the risk inherent to the operation of a UAS, by a given operator on a pre-specified location, hence simplifying the assessment needed to meet the requirements of the issuing of a permit to fly by the National Airworthiness Authorities (NAA). This framework was based on the RAT framework and implements new ways of assessing the risk, integrating it with a simple to use questionnaire to evaluate the probability of catastrophic failure, which is used to compute the probability of the UAS to hit a person or infrastructure on the ground.

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by The NATO Science and Technology Organization.

• Lieutenant Colonel Teresa Cabral Portuguese Military Airworthiness Authority. Lisbon. PORTUGAL Cranfield University, College Road, Cranfield. The UK. Corresponding Author: [email protected]
• Major Diogo Duarte Portuguese Air Force Airworthiness Certification Department. PORTUGAL  [email protected]
• Captain João Caetano (Ph.D.) Portuguese Military University Institute. Lisbon. Portuguese Air Force Research Center PORTUGAL [email protected]
• Prof. Simon Place Cranfield University, College Road, Cranfield. UK [email protected]
• Prof. Pete McCarthy Cranfield University, College Road, Cranfield. UK [email protected]