Toolkit: Complex Systems Toolkit.
Author: Dr. Ewa Ura-Binczyk (University of Warsaw).
Topic: Rail accident investigation and material failure analysis using systems thinking.
Title: Using fault tree analysis in a rail failure investigation.
Resource type: Teaching – Case study.
Relevant disciplines: Mineral, metallurgy & materials engineering; Civil engineering.
Keywords: Available soon.
Licensing: This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Related INCOSE Competencies: Toolkit resources are designed to be applicable to any engineering discipline, but educators might find it useful to understand their alignment to competencies outlined by the International Council on Systems Engineering (INCOSE). The INCOSE Competency Framework provides a set of 37 competencies for Systems Engineering within a tailorable framework that provides guidance for practitioners and stakeholders to identify knowledge, skills, abilities and behaviours crucial to Systems Engineering effectiveness. A free spreadsheet version of the framework can be downloaded.
This resource relates to the Systems Thinking, Systems Modelling and Analysis, Ethics and Professionalism, Technical Leadership and Critical Thinking INCOSE Competencies.
AHEP4 mapping: This resource addresses several of the themes from the UK’s Accreditation of Higher Education Programmes fourth edition (AHEP4): Analytical Tools and Techniques (critical to the ability to model and solve problems), and Integrated / Systems Approach (essential to the solution of broadly-defined problems). In addition, this resource addresses AHEP themes of Design, Ethics and Communication.
Educational level: Intermediate; Advanced.
Learning and teaching notes:
The case is built around 3 × 90-minute sessions and independent report writing. A suggested breakdown of the activities can be seen below.
Learners have the opportunity to:
- Explore how technical, human, and organisational factors interact in complex socio-technical systems.
- Apply Fault Tree Analysis (FTA) to diagnose ambiguous real-world engineering failures.
- Practice making judgements under uncertainty with incomplete and conflicting data.
- Analyse competing stakeholder perspectives and the ethical trade-offs in engineering decision-making.
- Develop professional communication skills by producing expert reports and presenting findings to a stakeholder panel.
- Reflect on their own reasoning, assumptions, and handling of complexity.
Teachers have the opportunity to:
- Use an authentic, narrative-driven case to introduce systems thinking and failure analysis.
- Facilitate active learning through group FTA construction and peer review.
- Engage students in interdisciplinary learning that links materials science, engineering practice, regulation, and ethics.
- Adapt the complexity of the case (technical vs organisational) depending on learners’ level and course focus.
- Provide formative and summative assessment using expert reports, presentations, and reflective writing.
- Encourage metacognitive development by prompting students to examine uncertainty and assumptions in engineering practice.
Downloads:
Learning and teaching resources:
| Session | Focus | Suggested activities and timing |
| 1 | Introduction and problem framing | 20 min: Introduce case scenario and system context; 30 min: Group discussion on initial impressions, key stakeholders, and potential causes; 40 min: Begin Fault Tree Analysis (FTA) construction using initial evidence. |
| 2 | Investigation and analysis | 30 min: Continue FTA construction and data evaluation; 30 min: Peer review of other groups’ fault trees; 30 min: Consolidate findings and prepare draft report outline. |
| 3 | Reporting and reflection | 30 min: Present findings to a simulated stakeholder panel; 30 min: Discuss feedback and defend conclusions; 30 min: Individual reflection on complexity, uncertainty, and assumptions. |
Summary of the system or context:
Rail transport systems consist of thousands of interdependent components, including rails, fasteners, sleepers, signalling systems, and maintenance processes. Failures in a single component can cascade, affecting:
- Safety: Malfunctions may cause derailments or delays.
- Economics: Service interruptions lead to financial losses and reputational damage.
- Public trust: Media scrutiny increases scrutiny of operational practices.
- Feedback loops: Delayed maintenance increases stress → failures occur more often → emergency repairs → less time for preventative work.
- Interdependencies: Material properties, environmental exposure, human inspection routines, maintenance schedules, and policy decisions interact.
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- Example: Poor inspection combined with extreme winter temperatures accelerates rail fatigue.
- Emergent behaviour: Minor flaws may accumulate and interact with environmental stressors, causing unexpected catastrophic failures.
- Stakeholders: Operator (service continuity), regulator (safety compliance), manufacturer (liability), passengers (safety and reliability).
Narrative of the case:
On a cold January morning, a commuter train was halted after inspectors discovered a fractured rail joint component. Services were disrupted for several hours, stranding thousands of passengers. The media quickly picked up the story, raising questions about safety and reliability.
The rail operator urgently commissioned an engineering consultancy (the students) to investigate the failure. Their findings will inform both the safety authority’s decision on whether the line can reopen and the legal proceedings to determine liability.
The dilemma:
- The operator demands a rapid report to resume services.
- The manufacturer insists the component was produced to specification and blames poor maintenance.
- The regulator requires an unbiased, defensible technical opinion before approving operations.
- The public expects transparency and reassurance about safety.
As consultants, students face incomplete evidence: some lab tests are missing, inspection logs are inconsistent, and eyewitness accounts conflict. They must use Fault Tree Analysis (FTA) to map possible causes, evaluate data, and produce an expert opinion report — knowing that their conclusions could influence legal outcomes and public safety decisions.
Groups: 3–5 students per group; 3-4 groups can run in parallel.
Materials required: case narrative handouts, sample inspection log, example FTA, whiteboards/flipcharts, sticky notes for FTA mapping.
Activity flow:
1. Introduce case and assign roles.
2. Construct initial fault trees using evidence.
3. Peer-review across groups.
4. Draft expert report and present to simulated stakeholder panel.
5. Individual reflection on complexity and uncertainty.
Why use Fault Tree Analysis (FTA):
FTA is a structured approach to trace a failure from an observed event back to potential causes, including technical, human, and organisational factors.
FTA is particularly suitable for this case because it allows students to structure complex, uncertain information in a logical and transparent way. It helps them trace the chain of causes behind the rail component failure, linking material, human, and organisational factors into one coherent framework. By visualising how small events combine into system-level failures, FTA encourages learners to think critically about interdependencies, data gaps, and assumptions. It also mirrors real-world engineering investigations, where professionals must justify conclusions under uncertainty and demonstrate clear reasoning to stakeholders such as regulators or courts.
Advantages in this case:
- Helps organise incomplete/conflicting evidence systematically.
- Visualises cause-effect relationships, interdependencies, and failure paths.
- Encourages discussion of assumptions and uncertainties.
Questions and activities:
- Discussion prompts:
| Prompt | Expected insight / reflection |
| What technical, human, and organisational factors might have contributed to this failure? | Students identify multiple interacting factors, illustrating interdependencies and emergent risks. |
| How does Fault Tree Analysis help structure uncertainty in this investigation? | Learners recognise FTA’s role in visualising cause-effect pathways and clarifying assumptions. |
| Which assumptions are you forced to make, and how might they affect your conclusions? | Students reflect on data gaps, biased observations, and ethical implications of assumptions. |
| How do different stakeholders’ interests shape urgency and framing of your analysis? | Learners understand trade-offs, pressures from conflicting priorities, and the precautionary principle. |
| What are the risks of issuing a preliminary report under time pressure? | Students explore implications for safety, liability, professional integrity, and public trust. |
- Classroom activities:
| Activity | Focus | What “good practice” looks like | Facilitator notes / tips |
| 1. FTA construction | Collaborative problem analysis | Teams discuss evidence openly, question assumptions, and co-create a logical tree linking technical, human, and organisational causes. | Encourage each group to identify at least one “human/organisational” branch and to label any data gaps explicitly. |
| 2. Peer review | Critical reflection and systems perspective | Groups provide constructive critique, highlighting hidden assumptions, missing branches, or unclear logic. Dialogue stays professional and evidence-based. | Provide coloured sticky notes or digital comments to record feedback; model how to frame critique as questions (“Have you considered…?”). |
| 3. Report writing (in-class drafting) | Synthesis and professional communication | Drafts show a clear, defensible reasoning chain from evidence to conclusion. Teams justify assumptions and note uncertainties. | Remind students to separate “facts” from “interpretations.” Encourage use of structured headings (Findings – Analysis – Conclusions). |
| 4. Simulation role-Play | Perspective-taking and communication under pressure | Presentations are concise (≤5 min), factual, and adapted to stakeholder roles. Learners respond respectfully and clearly to challenging questions. | Provide role cards for the panel (operator, regulator, manufacturer, public). Rotate students if possible. |
| 5. Reflection | Metacognition and learning from uncertainty | Students identify what surprised them, what they found ambiguous, and how their view of engineering judgment evolved. | Offer prompts like “What would you do differently next time?” or “Where did your reasoning feel uncertain?” |
Further challenge:
Instructors may choose to introduce a second “reveal” phase: a new metallurgical test result or a whistle-blower statement emerges halfway through the case. Students must revise their fault tree and defend whether and how their conclusions change. This highlights the evolving nature of complex systems investigations.
Assessment opportunities:
- Fault Tree Diagram (30%) – accuracy, depth, clarity.
- Expert report (30%) – structure, professionalism, evidence-based reasoning.
- Presentation and defence (20%) – clarity, stakeholder awareness, handling questions.
- Reflective summary (20%) – insight into uncertainty, assumptions, systems thinking.
Any views, thoughts, and opinions expressed herein are solely that of the author(s) and do not necessarily reflect the views, opinions, policies, or position of the Engineering Professors’ Council or the Toolkit sponsors and supporters.
