What is FTA Analysis?
FTA is critical for safety-critical systems where understanding and mitigating risk propagation is essential, from aerospace to nuclear energy. Tools like MADE automate FTA generation from system models, enhancing accuracy and speeding up iteration cycles. Here are how FTA Analysis are produced:
Top Event
The specific undesired system-level failure or hazard being analyzed (e.g., total system shutdown).
Logic Gates
Boolean operators (AND, OR, Voting) that define how lower-level failures combine to cause higher-level events.
Intermediate Events
Failure events that result from combinations of lower-level causes and contribute to the progression toward the top event.
Basic Events
The root causes of failure, such as individual component faults, software errors, or human actions, with no further logical decomposition.
FTA is typically applied at the system or subsystem level and is most effective when used during safety, reliability, or risk assessments. By visualizing causal pathways to failure, FTA supports rigorous analysis of critical events, making it essential for hazard identification, regulatory compliance, and mission assurance in complex systems.
The Structure of an FTA Analysis
Fault Tree Analysis (FTA) uses a structured, graphical approach to model the relationships between component level failures and a system-level undesired event, known as the Top Event. The structure of an FTA consists of various elements arranged hierarchically, allowing engineers to trace potential causes of failure back to their root sources.
The analysis begins with the Top Event, which is the failure scenario under investigation. From there, the tree expands downward using logic gates (such as AND, OR, or Voting gates) to connect Intermediate Events and ultimately the Basic Events or root causes. This structured representation provides a clear and logical breakdown of how faults can combine to cause critical failures. It also supports both qualitative analysis (e.g., identifying minimal cut sets) and quantitative analysis (e.g., calculating probabilities of occurrence), enabling informed risk-based decision-making.
FTA structures are especially powerful in regulated, safety-critical domains where traceability, justification, and rigorous hazard assessment are required.
The Structure of an FTA Analysis Diagram
| FTA Element | Description | Typical Source Information |
|---|---|---|
| Top Event | The undesired system-level event or hazard being analyzed. | System safety objectives, hazard analysis, preliminary hazard lists (PHL), regulatory requirements. |
| Failure Mode | The specific way in which a function or component can fail. | Historical failure data, subject matter expert input, standards (e.g., SAE J1739), and past FMEAs. |
| Intermediate Event | An event that occurs due to one or more lower-level events; lies between the Top Event and Basic Events. | Functional failure analysis, interface definitions, system design documentation. |
| Basic Event | A root cause failure with no further resolution; lowest level in the fault tree. | Historical failure data, reliability databases (e.g., MIL-HDBK-217), SME input, FMECA results. |
| External Event | A condition or event not under system control but influencing the fault tree logic. | Environmental specifications, operational assumptions, external interface requirements. |
| Undeveloped Event | An event not further analyzed, either due to lack of information or low impact. | Engineering judgment, scope definitions, low-criticality assessments. |
| Logic Gates | Symbols (e.g., AND, OR, Voting) used to represent how events combine to cause the parent event. | Reliability block diagrams, functional logic diagrams, fault propagation studies. |
| Transfer Symbol | Indicates a branch of the tree that is analyzed elsewhere to simplify large trees. | Large system fault trees, modular analysis, hierarchical decomposition. |
| Probability Data | Quantitative failure rates or likelihoods associated with Basic Events. | Reliability databases, statistical analysis, testing data, probabilistic risk assessment. |
| Cut Sets / Minimal Cut Sets | Combinations of Basic Events that can cause the Top Event; used for risk prioritization. | Generated by fault tree analysis tools or manual logic tracing. |
In a traditionally generated FTA, fault trees are manually constructed using static diagrams and spreadsheets based on expert judgment and qualitative reasoning. This manual approach can be time consuming, error-prone, and difficult to maintain, especially as system designs evolve.
In contrast, a model-based FTA, such as that enabled by the MADE platform, leverages a digital system model (e.g., a Digital Risk Twin) to automatically construct, update, and analyze fault trees. This ensures traceability, consistency, and real-time synchronization with design changes, enabling faster risk assessments, better decision-making, and compliance with safety standards throughout the system lifecycle.
What are the FTA Standards and Guidelines?
| Standard/Guidelines | Scope/Use |
|---|---|
| IEC 61025 | The primary international standard for Fault Tree Analysis. Defines the methodology, symbols, structure, and application of FTA for system safety and reliability assessment. Widely used across industries. |
| MIL-STD-882E | U.S. Department of Defense standard for system safety, including the use of FTA as part of hazard analysis and risk assessment in defense and aerospace systems. |
| ARP4761 (SAE Aerospace) | Aerospace Recommended Practice for conducting safety assessments, including FTA, in civil aircraft and systems development under ARP4754A guidance. |
| NPR 8705.5 & NASA-HDBK-0005 | NASA’s procedural requirements and handbook for performing model-based safety and reliability analysis, including FTA, in support of mission assurance. |
| IEC 61508 / ISO 26262 | Functional safety standards for electrical/electronic systems. Require FTA to identify and mitigate systematic failures in automotive, industrial, and safety-critical domains. |
| EN 50126 / EN 50129 | European railway standards requiring FTA as part of safety justification for signaling and control systems. Emphasize structured and auditable risk assessment. |
Types of FTA Analysis
Fault Tree Analysis (FTA) is not a one-size-fits-all method. Depending on the system complexity, lifecycle stage, and regulatory needs, different FTA approaches offer tailored insights for safety and reliability engineering. From early stage qualitative reviews to advanced model-based simulations, choosing the right type of FTA ensures effective risk identification, failure propagation analysis, and decision support. Below are six major types of FTA analysis used across industries today.
Qualitative FTA
USE CASES: Preliminary risk screening in early design stages.
This form of FTA focuses on understanding the logical structure of failures without assigning probabilities. It helps teams visualize how faults propagate and identify single points of failure, making it ideal for safety-critical concept design and system architecture reviews.
Quantitative FTA
USE CASES: Detailed risk assessment and probabilistic failure analysis.
Quantitative FTA assigns failure probabilities to basic events, enabling calculation of the top event likelihood. Common in aerospace, nuclear, and automotive systems, it supports reliability targets, safety certification, and risk-informed decision-making.
Dynamic FTA (DFTA)
USE CASES: Time-dependent system behavior and sequencing analysis.
DFTA incorporates temporal logic and system state changes over time, allowing analysis of systems where the sequence or timing of events impacts failure outcomes. It's crucial in real-time systems and advanced autonomous operations.
Common Cause FTA
USE CASES: Addressing non-independent failures.
This variation integrates common cause failures (CCF), where multiple components fail due to a shared cause. It enhances standard FTAs by preventing underestimation of risk in redundant or safety-critical architectures.
Modular/Hierarchical FTA
USE CASES: Large-scale systems with multiple subsystems.
Used when systems are too complex for a single flat fault tree, modular FTA breaks the analysis into manageable, reusable sub-trees. Ideal for aerospace, defense, and rail systems where component reuse and system-of-systems modeling is essential.
Model-Based FTA
USE CASES: Integrated digital engineering environments.
Model-Based FTA (like MADE) connects system models with FTA logic, enabling automatic generation, synchronization, and simulation of fault trees. It improves traceability, reduces manual errors, and supports digital twin strategies for continuous validation and certification.
Why FTA Matters in Today’s Engineering Environments
In today’s complex engineering environments, where systems are increasingly software-driven, interconnected, and safety-critical—Fault Tree Analysis (FTA) remains essential for identifying and mitigating catastrophic failures. A model-based approach to FTA elevates its value by embedding failure logic directly into the system model, enabling automatic fault tree generation, real-time updates, and deeper traceability across the design lifecycle.
This integration supports faster iteration, more accurate risk quantification, and better alignment with certification and safety requirements, making model-based FTA a cornerstone of modern systems engineering and digital assurance.
Traditional FTA - Why it falls short
While traditional Fault Tree Analysis has long supported safety and reliability efforts, it faces several limitations in today’s fast-paced, complex engineering environments:
- Manual Construction - Building fault trees by hand is time-consuming and prone to human error, especially in large systems with many dependencies.
- Static and Difficult to Update - Traditional fault trees are disconnected from design data, making them hard to maintain as systems evolve.
- Limited Traceability - There's often no clear link between fault tree events and the underlying system functions or components.
- Lack of Integration - Standalone FTA tools are rarely integrated into the digital engineering toolchain, reducing their usefulness in model-based workflows.
Why Model-Based FTA is Better
A model-based approach to Fault Tree Analysis (FTA) transforms it from a static, manually intensive process into a dynamic, automated, and fully integrated risk assessment solution. As engineering systems grow in complexity, Model-Based FTA is becoming the gold standard, offering superior accuracy, real-time updates, and seamless traceability. The future of FTA is model-based. MADE is model-based FTA Software. Here’s why this modern method delivers smarter, faster, and more reliable safety analysis:
Real-Time Synchronization
Automatically updates FTA models as system designs evolve, reducing rework and errors.
Improved Traceability
Links every event in the fault tree directly to system components and functions.
Automated FTA Generation
Quickly builds fault trees from system architecture, saving time and boosting consistency.
Faster Risk Assessment
Enables instant recalculation of failure probabilities and scenario analysis across the system.
Systems are Getting More Complex - Traditional FTA Process's Can't Cope
RAMS Content Engineer said: As engineering systems become more complex, interconnected, and software-driven, traditional FTA processes struggle to keep up. Manually built fault trees are difficult to scale, maintain, and align with evolving designs. Without integration into digital workflows, they fail to provide the speed, accuracy, and traceability needed for modern safety and reliability assurance.