Why Are Flights Delayed? The 5 Causes Airlines Report
By Sharon Ben-Moshe ·
US airlines report every delay in one of five official categories defined by the US DOT. Across 14.1 million US flights from June 2024 through May 2026, the single largest is late-arriving aircraft — the plane showing up late from its previous flight.
The five causes, by share of delay minutes
- Late-arriving aircraft — about 39%. Your plane was late on its prior leg. See how this ripple works.
- Air-carrier — about 34%. Causes within the airline's control: maintenance, crew, baggage, fueling.
- National Aviation System — about 20%. Air-traffic control, airport congestion, and weather managed by the system.
- Weather — about 6%. Extreme weather reported directly by the carrier.
- Security — under 1%. Evacuations, screening, or security breaches.
Why 'weather' looks smaller than you'd think
The 6% weather figure only covers extreme weather the airline logs itself. A large share of the National Aviation System category is also weather-driven — ground stops and flow control caused by storms. So weather's true contribution to delays is considerably higher than the standalone line suggests.
What you can actually control
You can't change the weather, but you can beat the ripple effect by flying early. See the best time of day to fly and the most delayed airlines to weigh your options before booking.
Frequently asked questions
What is the number one cause of flight delays?
Late-arriving aircraft — about 39% of all delay minutes. One late plane cascades into every later flight it operates.
Are most delays the airline's fault?
Combining the air-carrier and late-aircraft categories, causes tied to airline operations account for the majority of delay minutes.