Safety margins declined last week for the second consecutive week. Mean daily encroachment durations for January were 30 percent below the daily December average. However, the December daily average encroachment duration was by far the highest of any month in 2024. The January numbers only return the metric back to September levels and are 55 percent above the value for May 2024. 

​

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 February 1, 2025.

​

​

​

​

​

​

​

​

​

​

 

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.  

 

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. After last week’s second consecutive increase in buffer encroachment durations, the metrics are back  to the levels of September, before the big increases in November and December. Total encroachment durations for the week increased 6 percent and the number of encroachment events rose 20 percent. The number of weekly encroachment events has jumped 47 percent in just the past two weeks.

​

​

​

 

 

 

 

 

 

 

 

 

 

 

 

​

Figure 1. Weekly Buffer Encroachment Metrics

This week we continue reporting buffer encroachment durations by separation conformance category. This added detail is more informative to readers, as the Category PE and C buffer encroachments 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.  

​

Figure 2 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, primarily reflecting week-to-week variations in meteorological conditions. Last week the PE and C buffer encroachment durations more than doubled, while Category A and B duration totals for the week ending February 1 decreased 22 percent from the previous week. The metric is 53 percent above the low recorded in the first week of May. 

​

​

​

​

​

​

​

 

 

 

 

 

 

 

 

 

 

 

 

 

 

​​

Figure 2. Weekly Trends in Encroachment Durations By Separation Conformance Category

Figure 3 reports the 24-hour moving average encroachment duration of all conformance categories per aircraft for the past three months. Figure  also indicates the historical range of the data by showing the 25th, 75th, and 90th percentile values of the duration per aircraft metric. The percentiles were estimated using data from May 2022 through February 2024.

​

The chart shows a clear improvement in safety margins since the beginning of November although the variance is higher. Average daily encroachment durations fell in January, reversing the December trend, which was 24 percent above the November average. After last week’s decrease in encroachment durations, the Category A and B encroachment duration daily average for January was twenty-two percent below the December average.

 

 

​

​

​

 

 

 

 

 

 

 

 

 

​

​

​

​

Figure 3. 24-Hour Moving Average Encroachment Duration Per Aircraft for the Three Months Ending February 1, 2025

Figure 4 shows the longer trend in the 24-hour moving average since February 2024. This metric returned to its range from September and October and remains similar to February and March of 2024. Seasonal patterns appear to be persistent and we will continue to analyze the historical data to identify recurring patterns.

 

 

​