• Criteria by which probability is measured
    Description Qualitative Quantitative
    Probable Anticipated to occur one or more times during the entire system/operational life of an item. Probability of occurrence per operational hour is greater that 1x10-5
    Occasional Foreseeable to occur one or more times during the entire system/operational life of an item. Probability of occurrence per operational hour is less than 1x10-5 but greater than 1x10-6
    Remote Unlikely to occur to each item during its total life. May occur several time in the life of an entire system or fleet Probability of occurrence per operational hour is less than 1x10-6 but greater than 1x10-7
    Extremely remote Not anticipated to occur to each item during its total life. May occur a few times in the life of an entire system or fleet. Probability of occurrence per operational hour is less than 1x10-7 but greater than 1x10-9
    Extremely improbable So unlikely that it is not anticipated to occur during the entire operational life of an entire system or fleet. Probability of occurrence per operational hour is less than 1x10-9

    Criteria by which severity is measured
    Hazard classification Hazard severity
    Catastrophic Multiple deaths, usually with loss of aircraft
    Hazardous Large reduction in safety margins
    • Crew extended because of workload or environmental conditions
    • Serious or fatal injury to small number of occupants
    Major Significant reduction in safety margins
    • Difficulty for crew to cope with adverse conditions
    • Passenger injuries
    Minor Operating limitations
    • Emergency procedures
    • Nuisance
    Negligible Any other event not falling within the above categories