The Risk Analysis Tool (RAT) is a methodology used to classify safety related occurrences in the ATM domain. The methodology analyses two types of occurrences - Operational occurrences and ATM specific (technical) occurrences.
For operational occurrences, the risk exposure is analysed by taking into account the severity of the encounter and the repeatability or probability of such occurrences happening again. Severity of an encounter is defined by the risk of collision (achieved separation and rate of closure) and the amount of controllability which the controller had over the occurrence.
For ATM specific (technical) occurrences, the severity and the overall probability of recurrence is determined based on a combination of criteria (such as service provided and failure modes of systems that support ATS provision). The various combinations have been mapped in a look-up table which is at the heart of the methodology to define the safety risk posed by the combination of the technical failures and types of ATS provided. In order to ensure harmonisation in the determination of the severity of the ATM specific occurrences and the risk posed on the ATM system, the RAT has been designed and developed independently of any particular ATM system design.
The outcome of an occurrence assessment with the RAT methodology provides the risk which that occurrence posed on the ATM system, in particular on its ground part (ATC centre) but also on the overall ATM system (ground part and airborne part, including crew involvement).
The RAT is not a risk mitigation tool. It allows for analysis of a single event in order to understand the factors involved and then place the event in context with other events.