US flight delay causes explained
The US DOT attributes delays to five causes: air-carrier, extreme weather, National Airspace System (NAS), late-arriving aircraft, and security. Late-arriving aircraft is the largest single cause network-wide, which is why early-morning flights are often the most reliable.
Why it matters
The five delay categories the US DOT tracks — carrier, weather, NAS, late-arriving aircraft and security — and what each means for travelers. Use this alongside the route on-time pages and hub airport delay pages to interpret the numbers in context.
Frequently asked questions
Where does the data behind "US flight delay causes explained" come from?
From the US DOT Bureau of Transportation Statistics Airline On-Time Performance record. RouteOnTime's airport on-time and cancellation figures are real BTS data for full-year 2024; per-route figures are estimates derived from the endpoint airports. See the methodology page for details.
Is this guide specific to one airline?
No — these definitions apply across all US reporting carriers. Per-route and per-airport figures are on the route and airport pages.
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Last updated: 2026-06-13