What causes most flight delays?

In the 12 months through August 2026, 39.8% of all minutes of delay came from a late-arriving aircraft: a plane that left its last airport late. The airline itself (crew, maintenance, cleaning, fueling) caused 32.9%, the air traffic system 21.1% and severe weather 6%. Weather also hides in the other causes: BTS counts ordinary weather that slows traffic under the air traffic system.

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Key facts

Measure: % of all minutes of delay. Written from the data below.

  • Late-arriving aircraft has the highest figure, 39.8%.
  • Security has the lowest figure, 0.1%.
  • The highest is 398 times the lowest.

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Source and date

Source
U.S. Bureau of Transportation Statistics, Airline On-Time Performance (Reporting Carrier On-Time Performance, 1987–present)
License
Public domain (U.S. government work)
Data as of
Published

Citation

Chartly. “What causes most flight delays?” Chart. Data: U.S. Bureau of Transportation Statistics, Airline On-Time Performance (Reporting Carrier On-Time Performance, 1987–present), https://www.transtats.bts.gov/DL_SelectFields.aspx?gnoyr_VQ=FGJ&QO_fu146_anzr=b0-gvzr (data as of August 31, 2026). https://chart.ly/charts/causes-of-flight-delays (accessed November 4, 2026).

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The data

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The file has the numbers in this table, with the source, license and date. Please credit the source and Chartly. Developers can also get them as JSON (how).

Cause of delay % of all minutes of delay
Late-arriving aircraft 39.8
The airline (crew, maintenance, cleaning, fueling) 32.9
Air traffic system (congestion, airport, ordinary weather) 21.1
Severe weather 6
Security 0.1

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