Apportioned ATC Safety Criteria Based on Accident Rates

Abstract

Changes to safety critical operations need to be assessed and judged as acceptably safe before operational introduction. In Air Traffic Management (ATM), this good practice has been cast into the EUROCONTROL Safety Regulatory Requirement on Risk Assessment and Mitigation (ESARR 4), and the European Commission Regulation No. 2096/2005 laying down common requirements for the provision of air navigation services. A severe complication in applying these regulations is that, whereas one wishes to limit safety assessments to the parts of the operation that might be affected by the change, no criteria for acceptable safety of such parts are given. In other words, one needs to breakdown overall safety criteria and apportion the associated overall risk budget in order to be able to limit safety assessments. This paper presents such an apportionment. More specifically, an overall frequency per flight is derived for so-called Air Traffic Control-related accidents, which essentially correspond to the collisions Air Traffic Control (ATC) is to prevent and which can be objectively determined from accident data. The resulting overall ATC-related risk is apportioned over so-called ATC sub-products, which are to be interpreted as parts of flights forming a logical element within an ATC service or unit, such as ‘Taxiing’, ‘Line up’ and ‘Take-off’. The distribution of risk over the ATC sub-products is differentiated according to statistical accident and flight data. LVNL is currently in the process of gathering and categorisation of its incident data according to the developed ATC sub-products, to verify the derived apportionment based on accident data.It is obvious that very different circumstances may apply for the flights associated with a particular ATC sub-product: whereas one aircraft taxis a short route in good weather and quiet traffic circumstances, another aircraft taxies a long way, in poor weather and busy circumstances. Generally, the various circumstances are clustered into ‘states’ of the ATM system, which are characterized by weather, traffic condition and runway combination. For each ATC sub-product a risk acceptability interval around the average risk value is applied to allow for the different states in which the ATM system can exist.The ATC safety criteria are presented together with examples giving insight into their application, and it is indicated how expected traffic growth is handled.