Developing Safety Indicators for New Zealand Airspace

Abstract

The New Zealand (NZ) government actively sets safety targets for its airspace, and the level of safety traditionally has been measured by accident rates. However, numerous problems have arisen from the use of this indicator. With the Heinrich pyramid of common causation of accidents and incidents, focus has turned to the use of incident data–-particularly loss-of-separation (LoS) incidents between aircraft in airspace–-for safety indicators. This paper uses LoS data from New Zealand, Australia, and the United Kingdom to develop safety indicators specific to a particular airspace. A survey of previous research on factors affecting LoS incidents led to the selection of seven variables: airspace environment, altitude, traffic profile of the pair of aircraft in conflict, presence of one aircraft in altitude transition, geometrical configuration, causal agent (i.e., last human instigator of the incident), and degree of severity or risk of collision (i.e., level of risk reached during the LoS incident). A high-level data analysis is followed by log-linear categorical analysis to determine significant interactions between variables, and, on the basis of these interactions, specific safety indicators are obtained for NZ airspace. Significant interactions include type of airspace and aircraft in altitude transition, type of airspace and conflict geometry, aircraft in altitude transition and conflict geometry, and causal agent and severity. The results can be used to develop refined country-specific safety indicators and allow for targeted methods of improving safety.