About the Aviation Safety Monitor

The Aviation Safety Monitor is a service provided by Robust Analytics to deliver timely information on terminal area safety in the National Airspace System (NAS). The safety monitoring and prediction technologies were developed by Robust Analytics over the past several years. Partial funding was provided by the NASA Small Business Innovation Research Program and the NASA System Wide Safety Project.

The Aviation Safety Monitor provides quantitative estimates of safety margins at 26 airports in 17 metropolitan regions in the United States. This information complements data on several safety-related events that are published elsewhere, with the FAA’s Runway Incursion Statistics website a good example. However, the available safety information can be misleading if it only reports the frequency of violations with no insight into how safety buffers may vary minute-to-minute and day-to-day. The Aviation Safety Monitor aims to provide this insight every week.

How Do We Measure Safety Margins?

The Aviation Safety Monitor summarizes output from Risk Tracker, the Robust Analytics in-time terminal airspace hazard and safety metrics monitoring system.

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Aviation Safety Monitor Weekly Report for the Week Ending December 14, 2024

Safety margins continued to degrade last week, continuing the downward trend since late summer. Last week, the decrease in safety margins was driven by large increases in the Category PE and C separation conformance deviations. These buffer encroachment categories tend to be more frequent during instrument meteorological conditions that were more prevalent last week. Category A and B separation conformance deviations also remained near record highs last week. The past month saw the highest average daily encroachment durations since we started reporting in February. Safety margins have now decreased for five consecutive months.

Figure 1. Weekly Buffer Encroachment Metrics

Welcome back to the Weekly Aviation Safety Report. 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 December 14, 2024.

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.

Weekly Safety Margin Update. 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 changes in meteorological conditions. That said, the PE and C durations jumped up last week as low ceilings and visibility were more frequent around the NAS. The Category A and B durations report a very different story, with a strong upward trend since May. The Category A and B duration total for the week ending December 14 fell 14.7 percent from the previous week (which was, however, the highest recorded since February) but remained 2.2 times greater than the low recorded in the first week of May. The daily average encroachment durations for both conformance category groups are the highest for any month since February. Category A and B encroachment durations per event are also at their peak.

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

Figure 3 reports the 7-day moving average encroachment duration of all conformance categories per aircraft for the past three months. Figure 3 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 deterioration in safety margins since the beginning of November. The level has deteriorated and the variance has increased. Average daily encroachment durations in November were 22 percent above the daily October average. The October daily average was 7.5 percent higher than the September average, which was 10.4 percent above the August average. Daily encroachment durations were 10.2 percent higher in August than in July, and the July average was 16.4 percent higher than the June daily average. Average daily durations have now increased for five consecutive months, with the November daily average 79 percent higher than in April. The first two weeks of December are not encouraging.

Figure 3. 24-Hour Moving Average Encroachment Duration Per Aircraft for the Three Months Ending December 14, 2024

The long-term trends are even more obvious in Figure 4, which shows the 24-hour moving average for daily encroachment durations per aircraft across the in the 17 metropolitan areas that we monitor. The upward trend in average encroachment durations since June is readily apparent and the even greater increases since early November are worrisome.