Dependent Failure Analysis (DFA)
10 chapters You learn to prove that redundant channels and ASIL decomposition really are independent, running the six-step ISO 26262-9 Clause 7 method to hunt dependent failure initiators, coupling factors, and cascading paths across hardware and software.
How You Learn
Video and text stay in sync. As you scroll through the chapter, the video jumps to the matching explanation automatically.
Learning Objectives
Validate independence claims
Decide whether ASIL decomposition and redundancy claims hold by proving no single root cause bridges the channels.
Identify dependent failure initiators
Systematically surface the root-cause events and coupling factors that link elements you assumed were independent.
Run the six-step method
Apply the structured DFA process from element identification through coupling assessment to verified closure.
Select effective mitigations
Choose physical separation, diversity, partitioning, and monitoring measures that actually break the coupling you found.
Chapters
Why DFA Matters
Independence and redundancy claims collapse the moment a single root cause can defeat both channels at once, which is exactly what DFA exists to catch.
Common-Cause vs Cascading
Two distinct patterns by which one initiating event defeats several safety-relevant elements, with the normative definitions that keep your documentation precise.
Coupling Factors and DFI
The analytical core of DFA, where you identify dependent failure initiators and the coupling factors (shared power, clock, memory, environment) that connect supposedly independent elements.
DFA in the Lifecycle
DFA runs iteratively across the V-model rather than as a single gate, with defined inputs and outputs at the concept, hardware, and software phases.
The DFA Method
A structured six-step process that turns architecture documentation into a validated independence argument, complete with a reusable worksheet and the pitfalls to avoid.
Coupling-Factor Checklist
A category-by-category checklist (proximity, shared power and ground, shared memory and communication, common IP and tooling) so no plausible DFI path slips through.
DFA for Hardware
Hardware is where DFIs are most tangible, so this chapter covers shared power, shared die, and shared ground, plus a dual-core lockstep case study and a mitigation hierarchy.
DFA for Software
Software coupling rarely shows up in schematics, so this chapter exposes shared memory, shared operating system, and shared libraries that can silently break independence.
Worked Example
A complete DFA walkthrough for a dual-channel brake-by-wire architecture, moving from stated independence claims to a fully closed DFI register.
DFA vs FFI vs CCF
DFA, freedom from interference, common-cause failure, and cascading failure are four distinct but linked terms, and this chapter pins down each one for correct safety documentation.
Diagrams & Visuals
Common-Cause vs Cascading Animator
Animated contrast showing one shared root striking both elements at once versus a failure propagating element to element.
Coupling-Factor Radial Map
Radial view of coupling-factor categories around a pair of elements, exposing every shared resource and environment that could host a DFI.
DFA Lifecycle Timeline
V-model timeline placing DFA iterations at concept, system, hardware, and software phases with their inputs and outputs.
Redundancy vs Independence Comparator
Side-by-side comparison of redundant channels that share elements against channels with verified independence, showing how coupling erodes the benefit.
Freedom From Interference Partitioning
Memory, timing, and exchange partitioning between mixed-ASIL software components, highlighting where interference paths must be blocked.
Beta-Factor Sensitivity Curve
Sensitivity plot showing how the common-cause beta factor degrades the effective failure rate of a redundant pair as coupling rises.
Dual-Channel Brake-by-Wire DFA
A full DFA pass over a redundant pressure-sensor pair and a primary plus secondary ECU, working from the stated independence claims down to a closed DFI register.
- Map the architecture and list every independence and FFI claim it relies on
- Hunt DFIs across shared 5 V supply, shared CAN segment, and shared compartment
- Score each candidate by coupling strength and consequence severity
- Assign mitigations such as independent supplies, end-to-end protection, and physical separation
- Track open items and define the evidence needed to close each one
DFI Register Extract
Master Dependent Failure Analysis
Work through all ten chapters and turn fragile independence claims into evidence you can defend at an assessment.
Start Learning Now