> ## Documentation Index
> Fetch the complete documentation index at: https://docs.planeconnection.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Risk Assessment Matrix
> ICAO 5x5 risk matrix with severity levels, likelihood levels, and risk zones used in PlaneConnection.
PlaneConnection uses the standard ICAO 5x5 risk assessment matrix for evaluating safety risks. This matrix combines the severity of a hazard's potential consequence with the likelihood of that consequence occurring to produce a risk index. The matrix is the primary tool for Safety Risk Management (SRM) under 14 CFR Part 5 Subpart C, specifically 14 CFR 5.55.
## Severity Levels
Severity describes the worst credible outcome of a hazard if it were to result in an event.
| Level | Category | Description | Examples |
| :---: | ------------ | ------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
| **5** | Catastrophic | Multiple fatalities; aircraft destroyed. | Hull loss, fatal crash, multiple fatalities. |
| **4** | Hazardous | Large reduction in safety margins; serious injury; major aircraft damage. | Substantial aircraft damage, serious injury requiring hospitalization, significant reduction in ability to cope with adverse conditions. |
| **3** | Major | Significant reduction in safety margins; injury; minor aircraft damage. | Emergency landing, minor injuries, physical distress to passengers or crew. |
| **2** | Minor | Nuisance; slight reduction in safety margins; slight injury. | Minor incident, bruises, operating limitations, use of emergency procedures. |
| **1** | Negligible | No safety effect; no injury; no damage. | Near-miss with large margin, paperwork error, minor procedural deviation with no consequence. |
## Likelihood Levels
Likelihood describes how often the consequence is expected to occur, based on operational experience and available data.
| Level | Category | Description | Quantitative Guidance |
| :---: | ---------- | ------------------------------------------------------- | ----------------------------------------------- |
| **E** | Frequent | Likely to occur many times; has occurred repeatedly. | Greater than 1 in 1,000 flight hours or cycles. |
| **D** | Probable | Will occur sometimes; has occurred infrequently. | Between 1 in 1,000 and 1 in 10,000. |
| **C** | Occasional | Unlikely but possible; has occurred rarely. | Between 1 in 10,000 and 1 in 100,000. |
| **B** | Remote | Very unlikely; not known to have occurred but possible. | Between 1 in 100,000 and 1 in 1,000,000. |
| **A** | Improbable | Almost inconceivable that the event will occur. | Less than 1 in 1,000,000. |
## Risk Matrix
Each cell shows the risk index (likelihood + severity) and its risk zone. Rows represent likelihood (top = most frequent); columns represent severity (left = least severe).
| | **1 -- Negligible** | **2 -- Minor** | **3 -- Major** | **4 -- Hazardous** | **5 -- Catastrophic** |
| :-----------------: | :-----------------: | :--------------: | :----------------: | :----------------: | :-------------------: |
| **E -- Frequent** | 1E -- Tolerable | 2E -- Tolerable | 3E -- Unacceptable | 4E -- Unacceptable | 5E -- Unacceptable |
| **D -- Probable** | 1D -- Acceptable | 2D -- Tolerable | 3D -- Tolerable | 4D -- Unacceptable | 5D -- Unacceptable |
| **C -- Occasional** | 1C -- Acceptable | 2C -- Acceptable | 3C -- Tolerable | 4C -- Tolerable | 5C -- Unacceptable |
| **B -- Remote** | 1B -- Acceptable | 2B -- Acceptable | 3B -- Acceptable | 4B -- Tolerable | 5B -- Tolerable |
| **A -- Improbable** | 1A -- Acceptable | 2A -- Acceptable | 3A -- Acceptable | 4A -- Acceptable | 5A -- Tolerable |
## Risk Zones
| Zone | Color | Risk Indices | Required Action |
| --------------------- | ------ | -------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **Acceptable** | Green | 1A, 1B, 1C, 1D, 2A, 2B, 2C, 3A, 3B, 4A | Accept the risk. Document the rationale. No additional controls required, but monitoring continues under Safety Assurance (14 CFR 5.71). |
| **Tolerable (ALARP)** | Yellow | 1E, 2D, 2E, 3C, 3D, 4B, 4C, 5A, 5B | Reduce risk As Low As Reasonably Practicable. Implement controls to reduce severity, likelihood, or both. Cost-benefit analysis may be applied. Management acceptance required. |
| **Unacceptable** | Red | 3E, 4D, 4E, 5C, 5D, 5E | Do not proceed without risk controls that reduce the risk to at least the Tolerable zone. Operations must be stopped or modified until controls are in place. |
## ALARP Principle
**ALARP** stands for **As Low As Reasonably Practicable**. When a risk falls in the Tolerable zone, the organization must reduce it unless the cost of further reduction is grossly disproportionate to the safety benefit gained.
Demonstrating ALARP requires:
| Component | Description |
| -------------- | ------------------------------------------------------------------------------------------------ |
| Identification | All reasonably practicable risk controls are identified. |
| Evaluation | The cost (financial, operational, practical) of each control is assessed. |
| Implementation | Controls are applied unless the cost is grossly disproportionate to the risk reduction achieved. |
| Documentation | The rationale for the final risk acceptance decision is recorded. |
The burden of proof lies with the organization -- it must be demonstrated that no further practicable reduction is possible, not merely that the current level is adequate.
## Initial vs. Residual Risk
Every risk assessment in PlaneConnection includes two evaluations:
| Assessment | Description |
| ----------------- | --------------------------------------------------------------------------------------------- |
| **Initial risk** | The risk level before any controls are applied. Represents the inherent risk of the hazard. |
| **Residual risk** | The risk level after controls are applied. Represents the risk the organization is accepting. |
If the residual risk remains in the Unacceptable zone after all reasonably practicable controls have been considered, the operation or activity must not proceed.
## Risk Assessment Fields
| Field | Type | Description |
| ------------------------ | ---------------- | -------------------------------------------------------- |
| `hazard` | Reference | The hazard being assessed. |
| `severity` | Integer (1 -- 5) | Severity level of the worst credible outcome. |
| `likelihood` | Enum (A -- E) | Likelihood of the outcome occurring. |
| `risk_index` | Computed | Combination of likelihood and severity (e.g., `3C`). |
| `risk_zone` | Computed | `acceptable`, `tolerable`, or `unacceptable`. |
| `initial_risk` | Object | Severity, likelihood, and risk index before controls. |
| `residual_risk` | Object | Severity, likelihood, and risk index after controls. |
| `controls` | Array | List of risk controls applied or proposed. |
| `effectiveness_criteria` | Text | How the organization will measure control effectiveness. |
| `rationale` | Text | Justification for the risk acceptance decision. |
| `assessed_by` | User reference | The person who performed the assessment. |
| `assessed_at` | Timestamp | When the assessment was performed (UTC). |
| `approved_by` | User reference | The person who approved the risk acceptance. |
| `approved_at` | Timestamp | When the risk acceptance was approved (UTC). |
## Regulatory Alignment
| Regulation | Section | Requirement | Matrix Component |
| ------------- | --------- | --------------------------------------- | --------------------------------------------------------------- |
| 14 CFR Part 5 | 5.55(a) | Process to analyze safety risk | Severity and likelihood assessment |
| 14 CFR Part 5 | 5.55(b) | Acceptable level of safety risk | Risk zones and acceptance criteria |
| 14 CFR Part 5 | 5.55(c) | Risk controls when risk is unacceptable | Controls and residual risk evaluation |
| 14 CFR Part 5 | 5.97 | SMS records | Assessment records retained as long as control remains relevant |
| AC 120-92D | Chapter 5 | SRM guidance | Matrix methodology and ALARP documentation |
| ICAO Doc 9859 | Chapter 5 | Safety Risk Management | 5x5 matrix framework, severity and likelihood definitions |
## Related
Perform a risk assessment.
Explanation of SRM principles and philosophy.
Tutorial walkthrough of the risk assessment process.
How risk assessment integrates with Management of Change.