Trends in aircraft safety buffer encroachments levels and its evolution during Covid-19 pandemic

What is it about?

Separation assurance between aircraft is an important facet of the safety guarantee in the the National Airspace System (NAS). Separation requirement for aircraft are defined by horizontal and vertical separation buffers depending on the type of aircraft and type of airspace. The violation of these standards or encroachment into the separation buffers are indicative of reduced safety margins in the airspace. We analyze the buffer encroachment trends in the terminal airspace of 24 major airports in the U.S. over a period of 21 months from April 2019 to December 2020. The analysis measures the duration of encroachments within the terminal airspace for 15-minute epochs and the trends across the airports and their temporal evolution. The period at the beginning of the Covid-19 pandemic in mid-March 2020 and the slow recovery over the remainder of the year is of special interest as it provides a natural experiment for evaluating the impact of unusually low traffic density on aviation operations. Our analysis indicates that the airports show significant variability in the encroachment levels. Some airports like Dallas/Fort Worth International Airport (DFW) and Charlotte Douglas International Airport (CLT) show encroachment levels higher than expected during the reduced traffic period. Furthermore, the trends reveal spikes in encroachment levels during the pre-pandemic period at other airports like Atlanta International Airport (ATL) and Denver International Airport (DEN). The observed trends suggest the utility for real-time measurement of buffer encroachments across airports as a proxy for monitoring safety margin levels and aid the decision-making of different stakeholders.

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Photo by Beckett P on Unsplash

Photo by Beckett P on Unsplash

Why is it important?

The trust in commercial aviation relies on the high-levels of safety demonstrated by the aircraft and air traffic management systems. Identifying safety degradation in advance can help avoid catastrophic incidents. At the system-level (aircraft systems, communication systems, airport infrastructure, etc.), routine preventive maintenance schedules are standard practice to avoid any degradation. Similarly, standard operational procedures and predefined structures have been defined to ensure the human errors in air traffic management is minimized. However, deviations from these procedures are possible due to human errors or due to some environmental constraints. System-level safety metrics are an important way to track the overall compliance levels to predefined procedures and structures. The violation of safety buffers is an example of a system-level metric which can be used as a proxy for monitoring safety degradation. Currently, no system-level safety metrics are employed to continuously monitor the safety margin levels in the airspace. The analysis of buffer encroachment trends proposed here indicates that a near real-time measurement (e.g., for every last 5 minutes) of the same can give a continuous status monitoring tool for the decision-makers in the air traffic management system. We envisage buffer encroachments as one piece of a suite of safety/operational metrics that can help alert decision-makers to aspects of the airspace operations that warrant special attention.

Perspectives