Which Airlines Hold Up Late in the Day

Summary

Southwest Airlines loses 25.8 points of on-time performance between its 5–9 AM and 6–9 PM departures; Hawaiian Airlines loses 5.8. All 15 airlines in the data are more punctual on flights scheduled 5–9 AM than on flights scheduled 6–9 PM. Among the 12 carriers that reported every month, Southwest Airlines has the best morning record (92.3%) and SkyWest Airlines the best evening record (75.7%). The hours a carrier flies do not explain why some run better than others: scoring each carrier's flights at the rate the other carriers achieved in the same hour moves no carrier's all-day rate by more than 0.5 points, while the 12 differ by 10.5.

Each figure is the share of a carrier’s flights that arrived fewer than 15 minutes late, grouped by the hour the flight was scheduled to leave its origin airport, in that airport’s local time. A carrier that flies Boston to Los Angeles and back contributes to two different clocks. The six windows are the ones used across the site: 5–9 AM, 9 AM–12 PM, 12–3 PM, 3–6 PM, 6–9 PM and 9 PM–5 AM. The grid covers every airport in the DOT data, not only the airports FlyerIntel profiles, and it counts the carrier that operated the flight, so a flight sold by a mainline airline and flown by a regional one is credited to the regional.

Ranked by the fall from the 5–9 AM window to the 6–9 PM window. Every rate is a window with at least 120 flights, built from grid cells that each cleared the same floor. Each carrier’s fall compares it with itself over its own months, so it is shown for every carrier; the rankings and comparisons between carriers below use only the carriers that reported every month of the source period.

Only 12 of the 15 carriers reported every month of the source period, so the order below is among those 12. Endeavor Air (18 months), Hawaiian Airlines (30 months) and Spirit Airlines (35 months) reported fewer, and a carrier measured over fewer months, missing a different mix of seasons, is not like for like. Among them, first place changes hands through the day: Southwest Airlines at 5–9 AM, Republic Airways at 9 AM–12 PM, Delta Air Lines at 3–6 PM and SkyWest Airlines at 6–9 PM and 9 PM–5 AM. 12–3 PM has no clear leader: the top two are too close to call. Moving up: SkyWest Airlines from ninth to first and Alaska Airlines from tenth to fourth. Moving down: Southwest Airlines from first to seventh, Allegiant Air from fourth to ninth and JetBlue from seventh to twelfth. A carrier is named as leading a window only when its gap to the runner-up is larger than the flight counts would produce by chance. Flights on one day share weather and aircraft, so even that test is generous, and carriers within a point of each other should be read as level.

An hour is named only when it had at least 500 flights, and only when the best and worst are more than 5 standard errors apart, the rule the airport and airline heatmaps use. Hours are local time at the origin airport.

One explanation for the gaps between airlines is timing. A carrier that schedules more of its flying in the evening would look worse for it, whatever else it did. To check, each carrier’s flights at each hour were scored at the rate the other full-period carriers together achieved at that hour, and the result was weighted by how many flights the carrier had at each hour. Set against the rate those other carriers get over a whole day, the expectation is -0.5 to +0.2 points across the 12 carriers, which is what a schedule shape is worth. Their actual all-day rates run from 71.7% (Frontier Airlines) to 82.3% (Republic Airways), 10.5 points.

The full-period carriers only. The prediction applies the pooled rate of the other carriers at each hour to this carrier’s own flight counts by hour. Differences are taken from unrounded rates.

Share of scheduled flights that were cancelled, by the window the flight was scheduled to leave in. Cancelled flights are not in the on-time rates.

It cannot say whether the airline or its airports is responsible. A carrier’s evening flights leave from particular airports, and if those airports run slowly in the evening for every airline, the carrier’s evening figure is partly theirs. The grid has no airport dimension, so it cannot separate the two. What it does describe is what flying that airline at that hour has been like on the network it actually flies. The comparison of carriers at one airport is in “The Same Airport, Different Airlines.” The grid also mixes time zones, because each flight is placed by the clock at its own origin, and it includes holidays and weather events, which fall unevenly across hours and weekdays. It says nothing about why a carrier’s curve is steep or flat.