Safety margins continued to degrade last week, continuing the worsening trend since May. The number of buffer encroachment events in the most severe separation conformance categories increased 7.7 percent last week and total encroachment durations increased by 9.9 percent. Both risk metrics are the highest calculated since The Aviation Safety Monitor started the Weekly Report in February 2024. Daily encroachment durations in October are running 35 percent above the September average and are 98 percent above the May 2024 average. Average daily durations have now increased for five consecutive months.

Read the full Weekly Report for more information aviation safety changes.

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 October 26, 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 revise the weekly data chart to report buffer encroachment durations by separation conformance category. This added detail will be more informative to readers, as the Category PE and C buffer encroachments are highly 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 no obvious trend over the past eight months, primarily reflecting changes in meteorological conditions. The Category A and B durations report a very different story, with a strong upward trend since May. The Category A and B durations for the week ending October 26 increased 9.9 percent after increasing 35.6 percent the previous week. The daily duration average for October is 35 percent above that average for September and 2.3 times higher than the low weekly value for May 4. The encroachment duration metric is at the highest recorded value since the Weekly Safety Monitor began reporting in February.

Let’s now take a closer look at safety margins for the seven days ending October 26. Figure 3 displays estimates of encroachment durations per aircraft for each hour over the previous seven days. This offers a detailed look at how safety margins vary over the operating day. Figure 2 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.

Figure 3 displays the typical time of day pattern that we observe in the data, as encroachment events are highly correlated with traffic density. Even after aggregating the data over 17 metroplexes operating in three time zones the time of day pattern remains prominent. While there is only a handful of hourly reports above the 90th percentile, there are several reports each day above the 75th percentile.

Figure 4 reports the 7-day moving average duration per aircraft for the four weeks from September 15 through October 26, 2024. The moving average values are now consistently exceeding the 75th percentile threshold, indicating the negative trend even without many of the high-metric spikes reported in previous weeks.

Figure 5 displays the 7-day moving average encroachment duration per aircraft for the past three months. The chart shows a steady deterioration since the middle of July. Average daily encroachment durations in October are running 9.2 percent higher than the September average, which was 10.4 percent higher than 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 October daily average 50 percent higher than in April. The time series reflects a seasonal pattern in which safety margins are highest during the spring and summer months and slowly degrade starting in late summer. We are seeing that recurring pattern continue as we move into the autumn months.

Figure 6 shows the daily encroachment event rates and durations per aircraft across the 26 airports in the 17 metropolitan areas that we monitor. The blue bars report estimates of total daily encroachment durations divided by the number of aircraft in the terminal airspace (approximately 50 miles of the airport center) for all 17 terminal airspaces. The red line reports the daily number of encroachment events per 100 aircraft. We detect big jumps in both metrics the weeks ending July 27, August 11, and September 14, and October 26, with each peak higher than the previous one.