Efficiency Archives

Capacity, Efficiency, Safety • February 6, 2024

Understanding safety risks from another perspective – Bowtie

According to the initial investigation by the Japan Transport Safety Board, the recovered flight data and voice recorders indicate that the pilot misunderstood the ATC instruction and entered the runway without permission. Furthermore, it is suggested that the lack of monitoring by the ATC controller could have played a role in this unfortunate incident. This shows the complexity of aviation safety management which always involves many stakeholders. As a methodology focusing on specific events, the bowtie methodology may provide another perspective for the management of the major risks.

On January 2, a Japan Airlines A350, flight number JAL516, was involved in a collision with a Japan Coast Guard DHC-8 during its landing at Haneda Airport. Five of the six crew on board the DHC-8 died in the collision, but all 367 passengers and 12 crew on the A350 were evacuated without a fatality. Both aircraft were destroyed by the fire after the crash.

What is runway incursion and why does it happen?

ICAO defines a runway incursion as any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take-off of aircraft. The runway incursion may dramatically increase the risk of collision. Since runway incursion occurs during the landing or take-off phase of an aircraft, at least one of the involved aircraft will be running at a high speed, which increases the risk of aircraft damage, injury, and fatality. Due to its severe consequences, ICAO places it among the five highest-risk categories of safety events. The deadliest accident in aviation history, the Tenerife Airport disaster, which resulted in 583 fatalities, was also attributed to the runway incursion.

Many factors may induce this incident. According to the Global Action Plan for the Prevention of Runway Incursion (GAPPRI) developed by EUROCONTROL, the variability of human performance, lack of systemwide collision avoidance barriers, degraded runway status awareness, miscommunication and coordination, and challenges in surface navigation are the main reasons.

To reduce its occurrence and to mitigate its impact once it happens, all the stakeholders involved in the airport operations, including airport designers, airport operators, aircraft operators, air navigation service providers (ANSPs), ground handlers, manufacturers and the rescue and fire-fighting services (RFFSs), usually develop comprehensive regulations, procedures, training, and inspections from their own perspective. However, as a systemic incident, the prevention of runway incursion needs collaborative endeavors from many positions in various scenarios. Thus, it is necessary to introduce a comprehensive but concise method to deliver the risk management measures and the safety status to all related personnel.

Bowtie – understands runway incursion from another perspective

A bowtie diagram visualizes the risk you are dealing with in one understandable picture. The diagram is shaped like a bowtie, creating a clear differentiation between the proactive and reactive sides of risk management. The bowtie methodology provides another perspective on risk management. Different from traditional risk management which focuses on a specific position or process, a bowtie diagram is developed from an event.

With structured knowledge, different scenarios including the reasons and consequences of the event could be built up. Barriers could be set into scenarios to show what controls are in place to prevent, mitigate or eliminate major consequences from happening. Bowtie diagrams ensure easy risk communication by making the risk visual and understandable on the right abstraction level. Various colours, patterns or filters could be used to highlight the position in charge as well as the criticality and effectiveness of the barriers, which provides the safety manager with an overview of the entire risk management.

Bowtie methodology also provides solutions for the life cycle of risk management from proactive safety inspection to reactive incident investigations. Since all the processes are organized under the same method structure, the procedures could be simplified and the results could be presented in a clear, understandable and uniform way. Out of its benefits, the UK Civil Aviation Authority and other organisations have listed bowtie as a recommended method of risk management.

*To70 uses the Bowtie methodology to understand complex safety critical incidents and other issues.

Safety Oversight System to enhance the efficiency and effectiveness of National Civil Aviation Authority’s regulation processes

The Universal safety Oversight audit Program (USOAP) is a method developed by the International Civil Aviation Organization (ICAO) to assess and monitor the safety oversight capabilities of Member States. Nowadays, the USOAP will become the challenge for National Civil Aviation Authorities (CAAs) by many reasons such as data management, coordination effective, resources allocation etc. To meet these challenges, the Safety Oversight System has become the one of approaches, which help CAAs implement a centralized database, standardized processes and documents management. There is important in meeting the challenges of the future, as aviation systems become increasingly complex and new technologies are introduced. Now, let’s explore the advantages of implementing a Safety Oversight System in greater detail.

Advantages of using the Safety Oversight System

The Safety Oversight System, which are beneficial to stakeholders in aviation value chain, is able to improve efficiency, safety and cost-effectiveness.
>In recent years, CAAs have been implementing a Safety Oversight System in their aviation processes to improve efficiency, safety and cost-effectiveness which are beneficial to stakeholders in aviation value chain.

Improved Efficiency of Working Process

Safety Oversight System can lead to significant improvements in efficiency, particularly in the authorities where limited resource. By streamlining processes and reducing errors, digitalization can help aviation authorities to optimize their operations and maximize their resources.
For example, digitalizing the certification process can reduce the time and resources required to review and approve applications. By automating tasks such as document verification and record keeping, speed up the certification process and reduce errors. This can lead to faster processing times for applicants and ultimately improve the aviation industry’s safety and security.
Additionally, digitalization can also improve the efficiency of inspections and audits. By automating the collection and analysis of inspection data. This can help to prioritize resources and better target inspections and audits to ensure compliance with regulations.

Enhanced Safety and Security Oversight Standard

As an aviation authority, ensuring safety is of huge importance. Digitalization can greatly enhance safety in the aviation industry by providing aviation authorities with centralized database collection and analysis. This can enable them to take proactive measures to ensure the safety and security of air travel.
>For example, in the maintenance process, a Safety Oversight System can provide a structured approach to managing maintenance risks, from identifying potential hazards to implementing preventative measures. This can help aviation authorities to detect potential safety hazards early and take preventative measures to prevent costly and dangerous failures.

Increased Cost-Effectiveness

As an aviation authority, ensuring cost-effectiveness is important to efficiently allocate limited resources to enhance safety and operational effectiveness. The system can help aviation authorities to achieve cost savings and optimize resources allocation in the aviation industry.
>One way digitalization can improve cost-effectiveness is by streamlining processes and reducing the need for manual labor, which can reduce costs associated with time and labor. For example, digitalizing record keeping can reduce the need for physical storage and printing of documents, which can save on storage space and paper costs.

Example

Safety is important in aviation and the Safety Oversight System is a critical tool that ensures compliance with safety standards and regulations. Therefore, many applications of Safety Oversight Systems have become widespread to many CAAs who have been adopted for various work processes.
The example of the Safety Oversight System at work can be seen in the Aircraft Maintenance Organization process. Across many countries, aviation authorities grant certificates to these organizations to ensure compliance with safety standards and regulations. Similarly, acquiring a pilot license requires substantial effort from the aviation authority. The Safety Oversight System simplifies tasks like issuing certificates or licenses by consolidating them into a centralized database. This not only eliminates the need for paper-based processes but also allows for more organized management of applications via the system.

The centralized database greatly improves the efficiency of the Safety Oversight System by streamlining data management and making it easily accessible. This ensures that safety information is both accurate and current, facilitating better analysis of safety concerns. Easy access to information accelerates the safety oversight process, enabling safety inspectors and auditors to identify safety risks more rapidly and implement timely mitigations. In addition, the shared platform fosters better collaboration among stakeholders, further enhancing the system’s overall efficiency.
Moreover, the system aids in preventing counterfeiting by regulating the printing of certificates or licenses. These documents can only be printed at authorized locations where the operators or applicants are entitled to receive them. The Safety Oversight System also ensures that documents such as audit reports are managed consistently, simplifying future updates or layout changes.
>By streamlining data management, simplifying access, and promoting collaboration among stakeholders, the Safety Oversight System plays a crucial role in upholding and improving aviation safety standards.

On a final note

The aviation industry is constantly evolving, and the challenges it faces are becoming more complex and challenging. The implementation of a Safety Oversight System can help aviation authorities to overcome these challenges and enhance the efficiency and effectiveness of their regulation processes. Furthermore, the Safety Oversight System is one of keys tool that can help CAAs to prepare for the USOAP assessment. By implementing the Safety Oversight system, CAAs can demonstrate their commitment to safety and security and improve their chances of achieving a positive assessment.
>Countries such as the one discussed in the example have already implemented the Safety Oversight System, and other countries are likely to follow suit. By prioritizing safety, streamlining processes, and optimizing resource allocation, aviation authorities can ensure that the aviation industry remains safe, secure, and cost-effective for all stakeholders involved.

Air traffic control: How to deal with uncertainty?

On the 21^st of October last year I had the privilege to defend my dissertation titled: “Arrival Management in the Presence of Prediction Uncertainty”. In this blog, I will try to summarize what ended up being 11 years of work. It will describe where prediction uncertainty occurs, how the uncertainty may be determined and how that knowledge can be applied to visual interfaces and to algorithms.

Ref. M.Tielrooij, Arrival Management Support in the Presence of Prediction Uncertainty | TU Delft Repositories

Prediction uncertainty in Air Traffic Management

Modern Air Traffic Management systems use prediction of a flight’s trajectory as the basis for controller support. These applications include Short Term Conflict Alert (STCA), Medium Term Conflict Detection and Resolution CD&R, Arrival Management (AMAN), and flow/network management. Deliberately the above collection is ranked in terms of prediction horizon: The horizon is often determined by our ability to make a sufficiently accurate prediction for the application in which it will be used.

The accuracy of the prediction depends on the knowledge of the initial state of the flight, the knowledge of future events (weather, the intent of the aircraft but also of air traffic control), the degree to which we can model factors that influence the trajectory. With increasing horizon, the number and type of future events – or disturbances – increases. Hence, if we are no longer able to know and model these, the chance of a deviation between the prediction and the actual flown trajectory increases.

Different uncertainties for different flights

A lot of research has been, and is still being done, on increasing our ability to model. However, for applications such as arrival management (which rely on a desired prediction accuracy in the other of 10 seconds), the desired horizon is too large however. The European Regulation for Common Project One requires an AMAN horizon of 180 nm for Europe’s largest airports. London Heathrow, Paris Charles de Gaulle, Frankfurt Airport are all within 180nm from Amsterdam Schiphol Airport. Arrival management then invariably would require prediction (to the same order of magnitude of 10 seconds) of processes on the ground. With A-CDM requirements currently using a scope of 5 minutes as acceptable, this seems an impossible task.

If accurate predictions are not available, the next option is to make the system robust for uncertainty. The approach taken in my dissertation is to make the knowledge of uncertainty an integral part of the decision-making process.

Predicting uncertainty

The prediction accuracy is a key performance parameter in any ATM algorithm. In testing of the design, a generic accuracy is often determined that applies to all flights for which a prediction is made. Such an approach disregards that the accuracy can vary from time to time and even from flight to flight.

By analysing predictions from the EURCONTROL Network Manager, the dissertation develops a method that evaluates the properties of a flight to determine the actual prediction uncertainty. In this way the previously described horizon could be dynamically changed based on the accuracies of the predictions at that moment. Benefitting from that requires making the abstract concept of uncertainty meaningful in regards to operational constraints.

Ref. M. Tielrooij, C. Borst, M.M. van Passen, M. Mulder “Predicting Arrival Time Uncertainty from Actual Flight Information” – 11th USA/Europe ATM Seminar, 2025

Making the uncertainty visible

Prediction uncertainty in arrival management manifests as an uncertainty in time. The uncertainty is therefore a property of a property of a flight. This makes the concept particularly hard to visualise. By showing the potential effect of the uncertainty on the arrival management timeline, the dissertation translated the concept into an effect that can be related to constraints in decision making.

Ref. Tielrooij, D. Nieuwenhuisen, C. Borst, M.Mulder “Supporting Arrival Management Decisions by Visualising Uncertainty” SESAR Innovation Days 2013

Changing our strategies

The diagram proposed above proved hard to understand for experiment operators. One critical factor in their use of the diagram was the problem that uncertainty requires a different planning approach. Critical evaluation of the display ultimately provided another route to improve strategies. Based on the diagram an algorithm was developed that provides the horizon at which a sequence swap would be unlikely. Such an algorithm could support a dynamic working horizon based on the actual prediction uncertainty of the moment. A graduate student from the Delft University of Technology recently successfully applied the algorithm on a different prediction source to support debunching of inbound traffic.

Ref. E. Oosterhof “Effect of Trajectory Prediction Uncertainty on a Probablistic Debunching Concept for Inbound Air Traffic”, MSc theses, 2022

Conclusion

Prediction uncertainty is a hard problem but here to stay in aviation. This work showed pathways to start using it as another piece of information in decision-making. Within To70 I hope to apply the knowledge gained during my PhD to support ATM in working with it, rather than trying to avoid it.

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