Objective

To set out the common European risk classification scheme (ERCS) for the determination of the safety risk of an occurrence.

Summary

The ERCS addresses the safety risk of an occurrence and not its actual outcome. The assessment must determine the worst likely accident outcome that the occurrence might have led to, and how close to that outcome it was.

The ERCS is based on a matrix composed of two variables:

• severity - the worst likely outcome that would have resulted if the occurrence had escalated into an accident;
• probability - the likelihood of the occurrence to escalate into that outcome.

The identification of the severity of the potential accident outcome is a two step process:

• determination of the most likely type of accident (the so called "key risk area");
• determination of the potential loss of life category based on aircraft size and proximity to populated or high-risk areas.

The key risk areas are:

• airborne collision
• aircraft upset
• collision on runway
• excursion
• fire, smoke and pressurisation
• ground damage
• obstacle collision in flight
• terrain collision
• other injuries
• security

The potential loss of life is categorised by the number of possible fatalities (both in the air and on the ground):

• More than 100;
• Between 20 and 100;
• Between 2 and 19;
• One;
• Zero.

The severity score combines the risk area and the potential loss of life and is given as a single letter:

• A - no likelihood of an accident;
• E - an accident involving minor and serious injury (not life changing) or minor aircraft damage;
• I - an accident involving a single fatality, life changing injury or substantial damage accident;
• M - a major accident with limited amount of fatalities, life changing injuries or destruction of the aircraft;
• S - a significant accident with potential for fatalities and injuries;
• X - an extreme catastrophic accident with the potential for significant number of fatalities.

The Annex to the Regulation contains a table which combines the key risk areas, the potential loss of life categories and the severity score.

The probability of the worst likely accident outcome is obtained by using the ERCS barrier model. It assesses the effectiveness of the safety barriers which were remaining between the actual occurrence and the worst likely outcome. Ultimately, this model determines how close the occurrence has been to the potential accident.

The model consists of 8 barriers and each of them is assigned a weight:

• Aircraft, equipment and infrastructure design (weight 5);
• Tactical planning (weight 2);
• Regulations, procedures, processes (weight 3);
• Situational awareness and action (weight 2);
• Warning systems operation and action (weight 3);
• Late recovery from a potential accident situation (weight 1);
• Protections (weight 1);
• Low energy occurrence (weight 1).

The effectiveness of each barrier is classified as:

• Stopped if the barrier prevented the accident from occurring;
• Remaining Known if it is known that the barrier remained between the occurrence and the potential accident;
• Remaining Assumed if it is assumed that the barrier remained between the occurrence and the potential accident;
• Failed Known if it is known that the barrier has failed;
• Failed Assumed if it is assumed that the barrier has failed even if this cannot be determined;
• Not Applicable if the barrier is not relevant to the occurrence.

The weights of all barriers scored as stopped, remaining known and remaining assumed are summed. The result (a number between 0 and 18) is converted into a barrier score between 0 and 9 (9 meaning a score of 17-18, 8 - a score of 15-16, etc.).

The safety risk score is a two-digit value where the first digit is the severity score (A to X) and the second one is the barrier score (0 to 9). This code is then put into the ERCS matrix which is a table with barrier score on one axis and severity score on the other. The cells of the table are coloured to facilitate the determination of the urgency of the recommended action to be taken about the occurrence:

• RED colour means high risk (i.e. high number of fatalities combined with few barriers)
• YELLOW colour means elevated risk
• GREEN colour means low risk (i.e. either a lot of applicable barriers or few possible fatalities). Note however, that such occurrences may lead to increased risk scores when combined with other events.

Furthermore, each ERCS score is assigned a corresponding numerical value of risk magnitude to facilitate the aggregation and numerical analysis of multiple occurrences. These range between 0,000001 for an E9 occurrence (a risk of injury mitigated by a lot of barriers) and 1000000 for X0 (a catastrophic event with no barriers). The full spectrum is specified in the Annex to the Regulation.

Entry into Force

The Regulation entered into force in December 2020 and is applicable from 1st January 2021.

Regulation 2020/2034 supplementing Regulation 376/2014 as regards risk classification scheme (OJ, 11.12.2020)

Further Reading

European Commission

• EUR-Lex Portal: Regulation 2020/2034 (available in different languages and file formats)