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Framework for Unmanned Aircraft Systems Safety Risk Management
Abstract:
Although Unmanned Aircraft Systems (UAS) have now for some time been used in segregated airspace where separation from other air traffic can be assured, potential users have interests to deploy UAS in non segregated airspace. Recent technological and operational improvements give reason to believe that UAS safety and performance capabilities are maturing. But the skies can only really open up to UAS when there is an agreed upon UAS safety policy with commonly accepted UAS Safety Risk Management (SRM) processes enabling to show that the risks related to UAS operations in all the different airspace classes can be adequately controlled.
The overall objective is to develop a UAS SRM framework, supporting regulators and applicants through provision of detailed guidelines for each SRM step to be conducted, including 1) system description, 2) hazard identification, 3) risk analysis, 4) risk assessment, 5) risk treatment. The purpose is that all potential risks of the newly proposed UAS operations are controlled so that the existing safety level does not decrease (i.e. provides the baseline from which safety requirements for new proposed UAS operations are derived).
A survey of UAS activities provides an initial view on the risks and hazards to be considered, the needs and role of potential SRM users, the scope of the aviation system to be considered, the risks to be regulated, selection of suitable risk metrics, and the setting of an acceptable level of safety. It is motivated that the main safety risks that need to be addressed to ensure that UAS can be introduced in non segregated airspace without degrading safety are risks to other airspace users and third party risk (to objects on the ground). It will be necessary to show that these risks do not increase as compared to the current aviation system with manned aircraft only.
This paper focuses on the provision of guidelines for steps 2 to 4 of a UAS SRM process, covering both types of risks. The process for third party risk is based on a method that combines an accident probability model with an accident location model and an accident consequence model. This method enables evaluation of both individual risk and societal risk, and provides insight into probability and consequences of collision of a UAS with the ground. A method that addresses potential conflict scenarios (e.g. level busts, aircraft levelling of at the wrong flight level, flight track deviations due to operational errors) is proposed as basis for analysis of the risk of UAS to other airspace users. It is explained how the results may be used to build a Safety Case for UAS operations in non segregated airspace. Recommendations for application and validation of the proposed SRM process are also provided.