News Contacts

Fault Tree Analysis (FTA) Software

Safety Engineering RAMS Suite

Fault Tree Analysis (FTA) Methodologies & Software

Fault Tree Analysis (FTA) is a top-down, deductive root cause analysis method widely used in safety and reliability engineering. Using Boolean logic and visual tree diagrams, FTA identifies system failures by breaking down a major "top event" into its underlying component causes and basic events.

What is ALD Fault Tree Analysis (FTA) Software?

ALD FTA is an enterprise Fault Tree Analysis software designed for RAMS (Reliability, Availability, Maintainability, Safety) and System Safety engineers. It performs both qualitative and quantitative risk analysis, automatically calculates Minimal Cut Sets (MCS), failure rates, and system unreliability, and strictly complies with international standards such as ARP4761, ARP4754A, ISO 26262, MIL-STD-1629 and MIL-STD-882E.

Safety Commander's FTA module is a simplified FTAnalyzer fully integrated with Safety Commander's product tree and FMECA. It implements and summarizes the first-hand experience gained by ALD FTA experts in hundreds of projects using Safety Commander and other ALD software tools.

Initially developed for Aircraft (civil and military, helicopter, UAV, space)—which represent large, complex Systems of Systems—Safety Commander allows organizations, programs, and projects to resolve all challenges of assuring the safety of highly integrated systems. System structures can be imported from external applications or built manually in RAM Commander or Safety Commander.

Fault Tree Diagram Editor Safety Commander
Fault Tree Diagram Editor in Safety Commander
Engine Overview
Engine Module
FTAnalyzer
Integrated Safety Engine
Analysis Methods
Qualitative & Quantitative
Minimal Cut Sets (MCS), Worst-Case & Average
Standards Supported
ARP4761 • ISO 26262 • MIL-STD-1629A • MIL-STD-882E

Mathematical Formulas for FTA Calculation

Quantitative Fault Tree Analysis relies on probability and reliability equations to evaluate top-level event probabilities based on gate logic, basic event failure rates, mission duration, and operational profiles.

Basic Event Unreliability Q(t)
Q(t) = 1 - e^(-λ · t) ≈ λ · t
Calculates unreliability Q for a component with a constant failure rate (λ) over mission time t.
OR Gate Logic
Q_OR = 1 - ∏ (1 - Q_i)
The top event occurs if any input event occurs. For independent rare events, Q_OR ≈ ∑ Q_i.
AND Gate Logic
Q_AND = ∏ Q_i = Q_1 · Q_2 · ... · Q_n
The top event occurs only if all input events occur simultaneously (independent inputs).
Fussell-Vesely Importance
FV_i = Q_TOP(i) / Q_TOP
Measures the fractional contribution of basic event i to the total top event probability Q_TOP.
Worst-Case Unavailability
Q_WC(T) = Q(T) = 1 - e^(-λ · T)
Evaluates unreliability at the maximum mission time T (or at the end of an operating interval T) where risk reaches its peak.
Average Unavailability Q_AVG
Q_AVG = (1 / T) ∫_0^T Q(t) dt ≈ (λ · T) / 2
Calculates time-averaged unavailability over operating interval T for standby or periodically tested components.

Methodology & System Integration

Fault Tree Analysis is one of the most widely used methods in system reliability and failure probability analysis. A fault tree provides a graphical representation of logical structures depicting undesired failure events and their root causes using basic events and logic gates.

Fault Tree Basic Event Data Safety Commander
FTA Basic Event Data Input Screen
Fault Tree Minimal Cut Sets Safety Commander
Example of FTA Unavailability and MCS Analysis Report

After unavailability calculation and MCS analysis, Importance and Sensitivity Analysis helps engineers select events that contribute most to system unavailability or identify components where small changes drastically impact overall safety.

Fault Tree Events Importance Analysis Chart Safety Commander
Example of FTA Events Importance and Sensitivity Analysis Chart

FTA is uniquely indispensable in analyzing risks and determining combinations of hardware, software, and human failures. It is utilized by other Safety Commander modules, including the Safety Assessment Module (compatible with SAE ARP4761) and MMEL (Master Minimum Equipment List analysis).

FTA Calculation Workflow

Streamlined process for performing deductive safety assessment.

Step 1
Define Top Event

Specify the critical undesired system failure condition.

Step 2
Construct Tree

Build logic hierarchy using AND/OR gates & basic events.

Step 3
Import Parameters

Assign failure rates (λ), mission times, or unavailabilities.

Step 4
Calculate MCS

Automatically derive Minimal Cut Sets and gate probabilities.

Step 5
Importance Analysis

Evaluate Fussell-Vesely, worst-case, and sensitivity metrics.

Feature Highlights

Fault Tree Module Features

  • Modern Fault Tree editor with zoom and panning
  • Direct link between FTA and product tree
  • Automatic generation from FMECA
  • Import from CAFTA, Isograph, RAM Commander, PTC, OPSA
  • Calculation of large trees with MCS truncation control
  • Worst-case and time-averaged unavailability options
Explore FTA Module
System Compliance

Industry Standards Supported

Full compliance for aerospace, automotive, defense, and industrial safety requirement guidelines.

  • ARP4761 / ARP4754A (Civil Aviation)
  • ISO 26262 (Automotive Functional Safety)
  • MIL-STD-1629A & MIL-STD-882E
  • IEC 61508 / IEC 61511 Functional Safety
Software Overview

Connect With Our Engineering Team

Experience Safety Commander's Fault Tree Analysis module firsthand. Request an online demonstration to see how our software transforms system safety assessment.

Request Online Demo