Accident Severity Levels Explained

Aircraft Cabin

The primary purpose of airline risk management is to reduce the likelihood of being involved in an airline accident. Accidents, incidents, and occurences happen every day around the world, and categorising these events helps us better predict the future. These are industry defintions used by Airline Scope to help with the categorising and ranking of airline incidents.

Accidents & Incidents

The ATSB defines an accident as an occurrence involving an aircraft where:

  • a person dies or suffers serious injury;
  • the aircraft is destroyed, or is seriously damaged;
  • any property is destroyed or seriously damaged.

An incident is an occurrence, other than an accident, associated with the operation of an aircraft which affects or could affect the safety of operation.


Injuries to passengers and crew are also divided into serious and minor. These are defined in ICAO Annex 13.

A serious injury is an injury which is sustained by a person in an accident and which:

  1. requires hospitalization for more than 48 hours, commencing within seven days from the date the injury was received: or
  2. results in a fracture of any bone (except simple fractures of fingers. toes, or nose): or
  3. involves lacerations which cause severe hemorrhage. nerve, muscle or tendon damage: or
  4. involves injury to any internal organ: or
  5. involves second or third degree burns, or any burns affecting more than 5 per cent of the body surface: or
  6. involves verified exposure to infectious substances or injurious radiation.

Minor injuries are any injuries not considered to be serious. These defintions are helpful as they allow us to rank non-fatal accidents into their appropriate severity levels.

Severity Levels

The safety assessment mechanism used by Airline Scope defines five levels of accident severity. Any incidents outside of these definitions are considered minor and are excluded from assessments. Incidents are only included when carrying passengers (no cargo-only flights, no military flights), on fixed wing aircraft, that occurs between the time that boarding commences to the time that all passengers are disembarked.

Level 5
Any accidents/incidents resulting only in minor injuries or no injuries at all to the occupants and only minor damage to the aircraft.

This is the most common occurrence and covers common accidents and incidents that result in light damage to the aircraft or non-serious injuries to occupants. These happen, on average, once per day.

The most common of these occurrences are (but not limited to):

Level 4
Accidents involving serious injuries to passengers or crew and any accident involving major loss to the aircraft.

Slightly less common, this covers the most serious accident possible without a fatality. Level 5 and level 4 categories tend to overlap, though with more severe outcomes. Here are a few examples:

Level 3
An accident involving fatalities of 10 or less of the aircraft’s occupants.

This is entry level of the fatal accidents - ones that involves loss of life but still have a significant number of survivors. Some examples:

Level 2
An accident involving fatalities of more than 10 but less than 21 of the aircraft’s occupants.

Due to the narrow band between levels 3 and 1, this level is incredibly rare and usually involves smaller aircraft. Eg. Airlines PNG 4684.

Level 1
An accident involving fatalities of greater than 20 of the aircraft’s occupants.

The most serious level of accident. Some recent examples include:

Once each accident and incident has a severity rating, we are able to apply weightings which help with the assessment mechanism.