Towards Designing Graceful Degradation into Trajectory Based Operations: A Human-Machine System Integration Approach

Abstract

One of the most fundamental changes to the air traffic management system in NextGen is the concept of trajectory based operations (TBO). With the introduction of fundamental change, system safety and resilience is a critical concern, in particular, the ability of systems to 'degrade gracefully'. In order to design graceful degradation into a TBO envrionment, knowledge of the potential causes of degradation and appropriate solutions is required. Previous research has predominantly explored the technological contribution to graceful degradation, frequently neglecting to consider the role of the human operators in an environment in which humans, especially air traffic controllers, play a safety critical role. In addition, the environmental context in which the technological or human breakdowns occur also play a critical role in how well the system can degrade gracefully, which is also neglected in the literature. These oversights are out of step with real-world operations, and potentially limit an ecologically valid understanding of achieving graceful degradation in an air traffic control environment. Therefore, an integration approach to the human-machine system must be applied in order to achieve graceful degradation. The following literature review aims to identify and summarize the literature to date on the potential causes of degradation in air traffic control and the solutions that may be applied within a TBO context, with a specific focus on the contribution of the air traffic controller. A framework of graceful degradation, developed from the literature, is presented. The framework encompasses the potential impact of technology or human operator breakdown, as well as the complexity of the air traffic environment at the time of the breakdown, and categorizes them into different phases of detection and recovery. The aim of the framework is to develop research questions and design solutions to develop a resilient TBO system and procedures using a holistic view of human-machine system integration.

Designing graceful degradation into complex systems: The interaction between causes of degradation and the association with degradation prevention and recovery

“…Recurrent and relevant themes are presented below with illustrative quotes from participants. The presentation of results is organized by the order of research aims and address the primary elements of [3]'s framework of graceful degradation. Results are presented under five main headings: Main themes of degradation (p5) Frequently reported causes of degradation (p8) System degradation: The contribution of interactions (p12) Strategies to prevent and mitigate system degradation (p16) The notion of a system envelope (p19)…”

“…Of the available graceful degradation research, especially within the complex human-machine systems such as air traffic management (ATM), a majority of studies have focused primarily on the impact of technological causes of degradation and the ability of technology to prevent degradation. Although these research areas have provided excellent insight into the role of technology in gracefully degradation, non-technological causes of degradation (such as those arising from a non-optimal environment or from human operators), as well as contributions to degradation prevention or recovery, have been relatively neglected [3]. In an environment such as ATM, environmental factors, technological systems, and human operators are highly interconnected and can all influence the ability of a system to degrade gracefully.…”

“…After a systematic review of literature relating to graceful degradation in complex systems, [3] applied a humansystems integration approach to develop a framework of graceful degradation. This framework suggested that there were four main elements of graceful degradation -a degradation cause, identification of the degradation, prevention of impact on the system, and, if degradation occurred, recovery of nominal operations.…”

“…As a result, the potential interaction between the causes of degradation, and the resulting possible compound effect on the entire system, was under-researched. In addition, [3] identified a gap in research relating to the contribution of human operators in a gracefully degrading system. Human operators such as controllers, were expected to prevent degradation, or recover a degrading system once technological solutions were no longer viable, such as in aircraft emergencies, and failures or faults in software and hardware.…”

“…The current research aimed to contribute further understanding to the research gaps identified by [3], and review and extend the proposed framework of graceful degradation. Causes of degradation were defined broadly, as events that had the potential to negatively affect the wider ATC system in terms of safety and/or efficiency without mitigation.…”