Why ERC Is More Reliable Than the ICAO 5x5 Matrix in Risk Assessment

When assessing risk in aviation safety, one of the most common tools used is the ICAO 5x5 matrix. While widely adopted, it comes with a significant limitation: estimating “likelihood” often feels like guesswork, especially when dealing with rare but high-risk events.

That’s where the Event Risk Classification (ERC) model stands out.

Instead of trying to estimate how likely an outcome is, ERC asks a different question:

How many layers of defense were left between the event and an accident?

A Real-World Example: When the Last Line of Defense Fails

Consider this scenario:

🚨 A TCAS Resolution Advisory (RA) is ignored by the flight crew. They visually acquire the traffic and decide not to follow the RA. There’s no collision, but only by chance. Another aircraft could have been there, unseen.

How would this event be scored?

• ICAO 5x5 Matrix: Possibly a score of 10 (moderate severity, unlikely likelihood)

• ERC: 2500 — the maximum score

Why the huge difference?

👉 Because the final safety barrier failed. In this case, TCAS was the last remaining defense, and the only thing that prevented an accident was luck.

ERC Reflects Proximity to Catastrophic

This is the strength of ERC: It doesn’t just classify what happened—it tells us how close we came to a major event.

And because ERC assigns higher values to severe occurrences, they don't get buried in trend data. Instead, they stand out, prompting proactive action and better resource allocation.

Risk Assessment Grounded in Reality

When risk assessment is based on defense integrity instead of speculative probability, the result is a more accurate picture of operational safety.

ERC helps safety teams prioritize what matters most, detect weak signals in safety data, and support a strong, informed safety culture.