Expertise by Brendan Williams, Associate Technical Fellow, Insitu Pacific
Much of what we’ve learned over the last 100 years about developing Aviation Safety Regulations has been influenced by accident or incident. Tragedy and adversity have given rise to prescriptive regulations that provide a level of confidence and comfort for the global travelling public. So when it comes to the introduction of a new, relatively unknown technology into the National Airspace System (NAS) such as Unmanned Aircraft Systems (UAS), often the logical reaction is to ensure compliance with the established regulations. While this may seem like the most effective regulatory path forward, this approach begs the question – will this maximise or constrain, to the point of equivalency, the innovation available from new technology?
In Australia, the Civil Aviation Safety Authority (CASA) has been amenable to the “safety target” approach to compliance with Civil Aviation Safety Regulations (CASR) 101. A safety target approach requires a safety case that details risk and mitigations while identifying residual and acceptable risk levels. A set of agreed to safety objectives for UAS has yet to be defined, however terms such as “equivalent level of safety” or “acceptable level of safety”, or more formally “as low as reasonably practicable” are commonly used. With this approach applied to the introduction of UAS into the NAS, the aviation community is able to stand back, analyse, and recast the Aviation Safety Regulations as safety targets, rather than trying to develop technology that matches manned aviation assets or equally proscriptive solutions.
The Barrier Bow Tie Model introduces a new approach to risk analysis for UAS in the NAS by combining two well-established aviation risk models: Bow Tie, and the popular “Swiss Cheese” (Reason) Model. The Barrier Bow Tie model does not establish a safety target, but rather provides a framework to both structure and analyse a safety case for access to airspace. Each “barrier” consists of a number of controls, where each control is an opportunity to inject technology or procedures to reduce the probability of a mid-air collision. The model does not proscribe what controls must be used, rather it allows the user to select established technology or procedures, or to propose new ones.
It is the synergy and strength of the barriers that makes the argument (the safety case) of reaching the safety target. The formality and structure of the model allows a regulator to assess the safety case in a consistent manner. Importantly, the model does not identify “silver bullet” technologies, but rather emphasises the contribution of multiple barriers to reduce the probability associated with the mid-air collision risk. The combination of a consistent structure for assessment with the agility to select or even create the appropriate technologies or “controls” for each distinct case makes this model uniquely agile and reliable.
Australia is a world leader when it comes to airspace integration and testing of unmanned assets. Vast, open spaces, low air traffic complexity, a regulator willing to work closely with industry, all support a safety target approach to airspace access, including beyond Visual Line of Sight (BVLOS), in a safe and efficient manner. BVLOS operations require a joint effort by regulators and operators in meeting safety standards and levels of acceptable risk.
In Australia, Insitu Pacific has successfully worked with CASA in applying the Barrier Bow Tie Model to generate safety cases supporting the approval of BVLOS operations in the following scenarios.
Insitu Inc. also has conducted BVLOS operations in the United States as part of the FAA Pathfinder program when ScanEagle was used to demonstrate railway monitoring for BNSF in October 2015.
An approach to aviation safety regulation through the use of the Barrier Bow Tie Model places the emphasis on equivalency in safety, rather than equivalency in technology. This is a model that holds great potential to accelerate how global industry and regulators find a way to fly unmanned systems in the national airspace safely today.
Brendan Williams has more than 30 years engineering experience in the aerospace industry and is one of Australia’s leading experts in UAS risk and regulations. He is currently on assignment at Insitu Pacific from Boeing Research and Technology - Australia.