Neale L. Fulton

Measures of Societal Risk and Their Potential Use in Civil Aviation

This article seeks to clarify the conceptual foundations of measures of societal risk, to investigate how such measures may be used validly in commonly encountered policy contexts, and to explore the application of these measures in the field of civil aviation. The article begins by examining standard measures of societal and individual risk (SR and IR), with attention given to ethical as well as analytical considerations. A comprehensive technical analysis of SR is provided, encompassing scalar risk measures, barrier functions, and a utility-based formulation, and clarifications are offered with respect to the treatment of SR in recent publications. The policy context for SR measures is shown to be critically important, and an extension to a hierarchical setting is developed. The prospects for applying SR to civil aviation are then considered, and some technical and conceptual issues are identified. SR appears to be a useful analytical tool in this context, provided that careful attention is given to these issues.

Synthesis of Optimal Bang–Bang Control for Cooperative Collision Avoidance for Aircraft (Ships) with Unequal Linear Speeds

Close proximity encounters most often occur for situations in which participants have unequal linear speeds. Cooperative collision avoidance strategies for such situations are investigated. We show that, unlike the encounters of participants with equal linear speeds, bang–bang collision avoidance strategies are not always optimal when the linear speeds are unequal, and we establish the conditions for which no optimal bang–bang controls exist near the terminal time. Nevertheless, under certain conditions, we demonstrate that bang–bang collision avoidance strategies remain optimal for encounters of participants with unequal linear speeds. Such conditions are established, and it appears that they cover a wide range of important practical situations. The synthesis of bang–bang control is constructed, and its optimality is established.

Pilotless aircraft: the horseless carriage of the twenty‐first century?

This paper identifies recurring issues in the regulation of new technologies through an historical review of the risk management of automobiles in the 1800s. Parallels are drawn between the regulation of early automobiles and that of the regulation of Unmanned Aircraft Systems (UASs) today. It is found that many of the regulatory challenges facing UASs are analogous to those which faced the automobile industry more than a century and half ago and that the need for informed and objective decision making in policy development is reinforced. A systems engineering approach, based on general systems theory and decision‐based design principles, is then proposed as a means for improving the objectivity, transparency and rationality in the risk management decision making process. An example risk management decision making scenario is given within the context of a small UAS operating over a populated area. The results obtained from this case study illustrate how even simple analysis can support the decision making process and highlights some of the potential challenges in the regulatory approach currently applied to UASs.

Quantification of High Level Safety Criteria for Civil Unmanned Aircraft Systems

The civil Unmanned Aircraft System (UAS) sector is growing rapidly, with a notable orientation towards applications considered too dull, dirty, dangerous or demanding for conventionally piloted aircraft. Operations in this sector present hazards of two main kinds: to other aircraft, and to people and property overflown by UAS. Methods currently used for assessing these hazards and for managing safety and risk are less than comprehensive. This paper commences with a review of existing High Level Safety Criteria for UAS, including safety metrics, hazard metrics and risk metrics for manned aircraft operations and other modes of transportation. A set of quantified risk criteria for UAS operations is then developed, consistent with the As Low As Reasonably Practicable (ALARP) risk management framework used in current regulatory practice.

Formalising process scheduling requirements for an aircraft operational flight program

Formal methods are considered to be an important technique towards achieving the levels of assurance needed for high integrity systems. Formal specification is the essential part of the formal development process. The use of formal specification techniques on critical systems has shown significant growth in the last few years. In particular, there are a number of successful applications of using formal specification techniques in the aviation industry. Safety critical systems, such as aviation systems controlled by software, often have hard real time requirements. Producing the correct result at the right time is the fundamental goal of such systems. Formally specifying the system functions and the timing requirements is the crucial step towards achieving such a goal. Furthermore, aviation systems often need to be modified or upgraded on a regular basis, i.e. functionality and timing constraints may be altered. Therefore, the formal specification of such systems needs to be easily maintained and modified. We are interested in applying formal object modelling techniques to specify scheduling requirements of the multi parallel processes of an aircraft operational flight program (OFP). Our aim is not only to formalise the scheduling requirements for a particular aircraft, but more importantly to demonstrate an incremental and extendible modelling approach such that our model can be readily reused to specify other aircraft OFP scheduling requirements.

Modeling Aircraft Mission Computer Task Rates

Recently the Royal Australian Air Force (RAAF) has been considering an upgrade to the F/A-18 aircraft in Australia. This upgrade may well involve the modification of Mission Computer (MC) systems. Maintaining correct functionality for the upgraded F/A-18 is therefore a major concern for the RAAF. This particular problem received interest from CSIRO and DSTO to support a joint Research Fellowship to investigate specification of hard real-time characteristics by formal method approaches.

Synthesis of Optimal Control for Cooperative Collision Avoidance in a Close Proximity Encounter: Special Cases

Abstract The paper studies the optimal cooperative collision avoidance strategies in a planar close proximity encounter, with turning rates of the participants as the control functions. The maximization of the terminal miss distance is adopted as a performance criterion. This paper extends earlier analyses to the important special case when participants have unequal linear speeds but equal turn capabilities. The analysis is based on the Pontryagin maximum principle and the study of the properties of the extremals. The analysis is outlined in a unified manner that covers all special cases of the problem, including the cases of identical participants and the participants with unequal turn capabilities but equal linear speeds. The distinctive features of the mathematical structure of the problem and the optimal control solutions for different special cases of the problem are identified. The results of this paper are useful for setting and validating air traffic rules and for benchmarking and validating automated proximity management and collision avoidance systems.

An automated General Aviation Protection System for manned and unmanned aircraft

Achieving safe separation distances between aircraft, including UAVs, in controlled and uncontrolled airspace poses difficult challenges. Such challenges must be resolved if the full potential for safe UAV use in shared airspace is ever to be realized. The nature of the interaction of the traffic flow within a particular airspace determines the task-loading on pilots, UAV operators, air traffic service provider operators and on the communication systems required to manage aircraft proximity. In this paper we explore some of the theoretical behavioral characteristics arising in these systems and the implications for the design of safe operations using current data link systems. Traditionally, under voice communication traffic alerts were selective and in some cases sporadic in their delivery. Under proposed air traffic management systems utilizing GPS and data-link technology significant enhancements can be made to value add to the resultant situational awareness for pilots by automating the traffic alert protocol and by providing appropriate symbology on cockpit displays. A prototype architecture for testing automated proximity control of manned and unmanned aircraft, utilizing GPS and data-link technology, was recently developed and tested in Australian uncontrolled airspace as part of the Smart Skies Flight Test program. This architecture used both commercial cellular and satellite data links to connect aircraft flying in Australia, via the Internet, with an Automated Dynamic Airspace Control Centre (ADAC) located in the U.S. The architecture also allowed simulated aircraft, located anywhere in the world with Internet connectivity, to be flown with the real aircraft. Both simulated and real aircraft provided the ADAC with derived aircraft state data over the data links at rates of 0.5–2 Hz depending on the link and the test requirements. The ADAC provided automated Situational Awareness and, if needed, Separation Management instructions to the aircraft. The round trip latency of data on the network was on the order of three seconds. This paper combines the theoretical predictions using traffic flows with the Smart Skies test results to suggest the development of a General Aviation Protection System (GAPS). The challenges associated with implementing GAPS with commercial data link services on General Aviation aircraft and UAVs are discussed. Implementing a prototype GAPS within Australia is investigated.

Optimal bang-bang and singular controls in collision avoidance for participants with unequal linear speeds

We study optimal cooperative collision avoidance strategies for two participants with unequal linear speeds, but equal turn capabilities, in a planar close proximity encounter. Previous research showed that bang-bang strategies are optimal for participants with equal linear speeds. However, for participants with unequal linear speeds, bang-bang strategies are not necessarily optimal and, hence, singular control arcs may occur. We present a theoretical and numerical study of the structure of optimal controls with bang-bang and singular arcs. We prove that both controls can not be singular simultaneously and that the only possible singular control is a zero control. We derive formulas for the singular surfaces and verify that sufficient conditions hold for the computed extremal solutions. Different types of structural changes of the control strategies are identified.

Specific Length Trajectories Optimised for Maximum Acceleration using Conic Parameterised Clothoids

One current method of aircraft flightpath generation employs multi-segmented straight trajectories with each consecutive pair of segments filleted with arcs of constant radius. A difficulty of infeasibility immediately arises. In order for an aircraft to make the transition from a straight to a curved path segment (or vice versa) there is a physical requirement for a step acceleration, implying an infinite jerk. Clothoid curves provide a solution and have been investigated to fillet the consecutive segments. However, in this case, the mathematical definition of the clothoid is in terms of an integral that precludes closed-form solutions for critical guidance parameters. The attractiveness of the clothoid is to solve the physical infeasibility problem, however the mathematical intractability inherent in the approach has attracted limited attention despite being recognised as a major concern through early experiments. A method is presented here where double clothoid curves are used to fillet consecutive segments. This work goes beyond present practice to provide closed form solutions by using the hyperbola as a clothoid facsimile. Acceleration constraints have been enforced, both accumulative and maximum, and both the reference bank angle and bank angle rate have been expressed analytically in closed-form in terms of hyperbolic parameters. The solution can be optimised in terms of accumulative acceleration and path length, whilst simultaneously enforcing maximum acceleration constraints. This method of trajectory generation is attractive for implementation with air traffic management separation assurance, tunnel-in-the-sky, and other proposed cockpit display systems.