Aviation Safety Monitor Weekly Report for the Week Ending June 28, 2025

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Safety margins improved last week, remaining within the bounds in which they have fluctuated over the past two months. Total buffer encroachment durations in all separation conformance categories decreased 12.5 percent, primarily due to a 55 percent fall in Category PE and C buffer encroachments. Category A and B encroachment durations fell just 2.4 percent. Encroachment durations remain much higher than one year ago, with the daily mean increasing 72 percent from April through June 2024 to the same period this year. The mean daily number of encroachment events rose 18.5 percent and mean daily duration per event jumped 45 percent.

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Weekly Safety Margin Update. Every Monday Robust Analytics reports on safety margins at 26 United States airports. With this Aviation Safety Monitor Weekly Report, Robust Analytics offers the aviation community timely assessments of changing safety margins and safety-related events. Dates and times are tracked in UTC and the week ends at midnight every Saturday. This week’s report includes data through 2400 UTC on June 28, 2025. 

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For New Readers: Please read our article “Did Safety Degrade in the National Airspace System in the Winter of 2022-2023?” that applies our methods and data to examine whether safety margins decreased during the events of winter 2022-2023.  https://www.linkedin.com/pulse/did-safety-degrade-national-airspace-system-winter-kpq8e/?trackingId=dLIUDpIMzA34g3H4GDwrHw%3D%3D

The Aviation Safety Monitor measures safety margins by estimating the frequency, duration, and severity of buffer encroachments. Our paper “How Do We Measure Safety Margins?” provides a detailed description of the methods and data. That article can be found here https://www.robust-analytics.com/measure  on the Robust Analytics website.

The Weekly Safety Report uses buffer encroachment events and durations to measure changes in safety margins. Safety margins fell last week but within the moderate range of the past couple of months. Total encroachment durations decreased 12.5 percent and the number of encroachments dropped 10.3 percent.

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Figure 1. Weekly Buffer Encroachment Metrics at 26 Airports

The NAS is simply not showing the improvements in safety margins that we expect at this time of the year. The seasonal pattern for the previous two winters saw safety margins decline from September to December but then begin to improve steadily through the summer. That pattern is not holding this year, as safety margins remain stubbornly low into early summer. The mean daily buffer encroachment duration for May was unchanged from April, when we expected significant improvement from better weather and longer days. The mean daily encroachment duration for Category A and B events during the first four weeks in June are seven percent higher than in May. Mean daily buffer encroachment durations are 72 percent higher for April 1 through June 28, 2025 than the same period one year ago.

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Buffer encroachments are classified into four separation conformance categories based on the severity of separation deviation. Category PE and C buffer encroachments identify relatively weak separation conformance deviations and are strongly affected by meteorological conditions. In fact, by definition, during visual meteorological conditions there are no buffer encroachments. The more severe encroachments in Category A and B provide a better indicator of changing safety margins.  

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This conclusion is illustrated by Figure 2 that reports mean daily total encroachments durations by separation conformance category. There are fewer Category PE and C encroachments and they peak in the winter months. In previous years, Category A and B buffer encroachments would peak in the winter months and they gradually decline. In 2025, however, the decline has been modest and Category A and B mean daily encroachment durations for April 1 through June 28 are 74 percent higher than the same period one year ago.

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Figure 2. Mean Daily Buffer Encroachment Durations By Month

Figure 3 reports the weekly total durations for the two conformance category groupings. The Category PE and C weekly durations bounce around with little long-term trend since we started reporting in February 2024, primarily reflecting week-to-week variations in meteorological conditions and some seasonal variation. Last week the PE and C buffer encroachment durations fell 55 percent, while category A and B duration totals decreased 2.4 percent, for a net decrease of 12.5 percent.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 3. Weekly Trends in Encroachment Durations By Separation Conformance Category

Figure 4 reports the 7-day moving average of hourly buffer encroachment durations in all conformance categories since February 2024. The pattern is very clear, as the historical behavior of increasing buffer encroachments from the summer low into winter held, but we are not seeing the improvement expected in the first six months of 2025. Buffer encroachment durations rose in September and October, then bumped up again in November and have remained high ever since. Variance improved over the past two months with fewer disturbingly high encroachment periods but the overall level is high. Visual examination of Figure 4 suggests that buffer encroachments increased in October 2024 and have remained at a new, higher plateau ever since.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 4. Seven-Day Moving Average of Daily Buffer Encroachment Durations From February 18, 2024 Through June 28, 2025