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By following this guide, you will identify root causes during a safety investigation using one of three structured RCA methods: 5 Whys, Fishbone (Ishikawa), or Barrier Analysis. Each method produces documented findings that feed into investigation recommendations and CPAs.
Who should read this: Lead investigators and investigators conducting safety investigations. Safety managers who review investigation findings will also benefit from understanding the methodologies.Prerequisites: An active investigation in Data Collection or Analysis status. Familiarity with the investigation workflow (see Manage Investigations).

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Choose the Right Method

PlaneConnection supports three RCA methods. Each is suited to different types of events. You may use more than one method on the same investigation if the complexity warrants it.
When in doubt, start with the Fishbone method to map out all potential contributing factors, then use the 5 Whys to drill into the most significant branches. This combined approach works well for moderately complex events.

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Method 1: 5 Whys

The 5 Whys method traces a causal chain from the event back to its root cause through iterative questioning. Each “why” peels back a layer of causation until the fundamental systemic issue is revealed.

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Conduct a 5 Whys analysis

The “5” in 5 Whys is a guideline, not a strict rule. Some root causes surface in 3 levels; others require 6 or 7. Stop when you reach a systemic cause that the organization can act on. If you find yourself asking “Why?” and the answer is outside your organization’s control (e.g., “because physics”), you have gone too far.

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Method 2: Fishbone (Ishikawa)

The Fishbone diagram organizes contributing factors into six standard categories, providing a structured view of all the conditions that may have contributed to the event. This method is particularly effective for complex events where multiple factors across different domains interacted.

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Categories

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Conduct a Fishbone analysis

Conduct the Fishbone analysis collaboratively when possible. Different perspectives — flight crew, maintenance, dispatch, management — often reveal factors that a single investigator might miss. The six categories serve as prompts to ensure you consider all domains.

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Method 3: Barrier Analysis

Barrier Analysis examines the defenses — physical, procedural, and administrative — that should have prevented the event, and identifies where they failed, were bypassed, or were absent.
For the full field definitions and barrier status reference, see Investigation Workflow.

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Conduct a Barrier analysis

Barrier Analysis requires a thorough understanding of what defenses should exist. If your organization has not formally defined its barriers for a given hazard, the analysis itself becomes a valuable exercise in identifying what controls need to be established. Document missing barriers as absent and create CPAs to implement them.

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From root causes to recommendations

Regardless of which RCA method you use, the output follows the same path:
  1. Each root cause should produce at least one recommendation.
  2. Recommendations become CPAs when the investigation is approved (see Create a CPA).
  3. CPAs are tracked through implementation and verification, closing the loop from event to resolution.
Per ICAO Annex 13 principles, the purpose of investigation and RCA is prevention, not blame. Focus your analysis on systemic and organizational factors — procedures, training, oversight, design — rather than individual performance. Root causes that point to “the person made a mistake” should be followed further to ask “what systemic conditions allowed or encouraged that mistake?”

Manage Investigations

Full investigation workflow from assignment through approval.

Investigation Workflow

Statuses, RCA methods, and approval rules reference.

CPA Lifecycle

How investigation recommendations become tracked corrective actions.

Run Your First Investigation

Tutorial walkthrough of the complete investigation process.
Last modified on April 11, 2026