This 5 × 5 aviation risk assessment matrix combines five probability levels with five severity levels. It helps you assess a possible outcome of a hazard and decide whether the risk needs further action.
The example is based on the International Civil Aviation Organization (ICAO) Safety Management Manual, third edition. This page explains its aviation ratings, including what a code such as 4B means. You can also download the matrix in PowerPoint and PDF.
How to read the aviation risk assessment matrix
Start by describing the outcome you are assessing. For example, “vehicles operating near parked aircraft” describes a hazard. “A vehicle strikes an aircraft and causes major damage” describes a possible outcome you can assess.
- Choose the probability row. The rows run from Frequent (5) to Extremely improbable (1).
- Choose the severity column. The columns run from Catastrophic (A) to Negligible (E).
- Read the cell where they meet. Occasional (4) and Hazardous (B) give the risk index 4B.
- Check the cell’s tolerability category. Use this to identify the action and approval needed under your organisation’s safety process.
What does 4B mean?
4 = Occasional. B = Hazardous. The number and letter form a reference to a cell. You do not multiply them, and the result is not a percentage chance of an accident.
Aviation risk severity definitions: A to E
Severity describes how serious the consequences could be. In this example, A is the most severe category. These plain English summaries explain the ratings used on the matrix.
| Severity | Meaning in this example | Letter |
|---|---|---|
| Catastrophic | Multiple deaths or the destruction of equipment. | A |
| Hazardous | A large loss of safety margins; distress or workload that prevents reliable task performance; serious injury; or major equipment damage. | B |
| Major | A significant loss of safety margins or reduced ability to cope with difficult operating conditions; a serious incident; or injury. | C |
| Minor | Disruption, operating restrictions, use of emergency procedures or a minor incident. | D |
| Negligible | Little consequence. | E |
Notice that major equipment damage belongs to Hazardous (B) in this example. Read the definition, rather than choosing a category because its name sounds right.
Aviation risk probability definitions: 5 to 1
Probability describes how likely the assessed outcome is. The highest rating is 5. Use the same outcome for both probability and severity: the frequency of vehicles passing an aircraft is different from the likelihood of a damaging collision.
| Probability | Meaning in this example | Number |
|---|---|---|
| Frequent | Expected repeatedly, with a history of frequent occurrences. | 5 |
| Occasional | Expected from time to time, with some previous occurrences. | 4 |
| Remote | Possible but unlikely, with only rare previous occurrences. | 3 |
| Improbable | Highly unlikely, with no known previous occurrence. | 2 |
| Extremely improbable | So unlikely that it is difficult to imagine it occurring. | 1 |
These are descriptive categories. They do not set numerical limits per flight, operating hour or year. Record the evidence and assumptions behind your choice, so another assessor can understand it.
What do the red, amber and green zones mean?
The colour groups the risk index into a tolerability category. Tolerability means whether the organisation can accept the risk, and under what conditions.
| Safety risk index range | Safety risk description | Recommended action |
|---|---|---|
| 5A, 5B, 5C, 4A, 4B, 3A | Intolerable | Take immediate action to reduce the risk or stop the activity. Give risk reduction priority. Put additional or stronger preventive controls in place to bring the risk index into the tolerable range. |
| 5D, 5E, 4C, 4D, 4E, 3B, 3C, 3D, 2A, 2B, 2C, 1A | Tolerable | The risk may be tolerated with suitable measures to reduce it. A management decision may be needed to accept the remaining risk. |
| 3E, 2D, 2E, 1B, 1C, 1D, 1E | Acceptable | The risk is acceptable as assessed. This example does not require further measures to reduce it. |
For example, 4B is intolerable, while 2B is tolerable. Moving from 4B to 2B changes the action needed, but does not move the risk into the green, acceptable group.
These groups apply to this example. Apply your organisation’s own criteria and approval rules when using a matrix operationally. An acceptable rating assumes that the controls and conditions used in the assessment remain in place.
For related guidance on risk acceptance, see CAA CAP 1059, paragraphs 3.25 to 3.27, which uses the categories unacceptable, review and acceptable.
Worked example: a ground vehicle collision
Illustrative example: a ground handling team is assessing vehicle movements beside parked aircraft. The scenario and ratings below are invented to explain the method; they are not accident data or an assessment of a particular airport.
From a hazard to a risk index
Hazard: ground vehicles operating close to parked aircraft.
Assessed outcome: a vehicle strikes an aircraft and causes major equipment damage.
Probability: assume the team rates this outcome Occasional (4), taking existing controls into account.
Severity: major equipment damage falls under Hazardous (B).
Risk index: 4B. Find row 4 and column B. This example requires action to reduce the risk.
The team could investigate changes to vehicle routes, separation from aircraft and arrangements for manoeuvring. Each proposed control needs an owner, a completion date and a way to check whether it works.
Suppose later evidence supports changing the probability to Improbable (2). If a collision could still cause the same damage, severity stays at B and the revised index becomes 2B. The team must check that cell and obtain any required acceptance. A lower probability alone does not make the risk acceptable.
Record the original assessment, controls and reassessment in a risk register or hazard log. The CAA describes this record and review process in CAP 1059, paragraph 3.31.
Download the aviation risk assessment matrix
Download the free 5 × 5 matrix for a presentation, workshop or reference sheet.
PowerPoint and PDF files
Need the older format? Download PowerPoint (.ppt).
Using the template: this is an educational example based on the cited ICAO edition. For an operational aviation assessment, use the definitions, thresholds and approvals established in your organisation’s safety management system. Changing a cell’s colour does not reduce the underlying risk.
Other risk assessment matrix examples
For a different scale, see the simple 3 × 3 risk assessment matrix or the 4 × 4 risk assessment matrix. For the wider process, read our risk assessment guide.
Sources and further reading
- ICAO, Safety Management Manual (Doc 9859), third edition, 2013. Original source cited for this matrix: Figure 2-11, probability, and Figure 2-12, severity, printed pages 2-28 and 2-29. The definitions above are plain English adaptations. Safety Management Manual in the ICAO eLibrary.
- UK Civil Aviation Authority: CAP 1059. Chapter 3 explains risk assessment, tolerability, mitigation and hazard logs.
- UK Civil Aviation Authority: safety management systems. Explains how assessment and mitigation fit within an organisation’s wider safety arrangements.
