FlyerIntel Research
What Causes Delay at Big and Small Airports
Late aircraft is 39.5% of delay minutes at the largest third of airports and 42.2% at the smallest.
Published October 18, 2026 · Source period July 2023 – July 2026
Summary
Late aircraft is 39.5% of reported delay minutes at the largest third of covered airports and 42.2% at the smallest. Weather is 5.8% and 4.6%.
Key findings
- Largest third: late aircraft 39.5%, weather 5.8%, air traffic system 20.0%, carrier 34.5%.
- Smallest third: late aircraft 42.2%, weather 4.6%, air traffic system 21.2%, carrier 31.9%.
- The widest gap between the largest third and the smallest third is late aircraft, 2.7 points.
- Per completed flight, the largest third carries 15.9 reported delay minutes and the smallest 14.1.
- No cause lines up clearly with airport size.
Where the delay minutes come from, by airport size
| Group | Airports | Carrier | Weather | Air traffic system | Security | Late aircraft | Carrier and late aircraft |
|---|---|---|---|---|---|---|---|
| Largest third | 21 | 34.5% | 5.8% | 20.0% | 0.1% | 39.5% | 74.0% |
| Middle third | 21 | 31.1% | 4.6% | 20.7% | 0.2% | 43.5% | 74.5% |
| Smallest third | 22 | 31.9% | 4.6% | 21.2% | 0.1% | 42.2% | 74.1% |
Each figure is that cause’s share of the delay minutes the DOT assigned to the five causes together, with the minutes of the airports of a group added up before dividing, so a large airport weighs more than a small one inside its group.
Delay minutes per completed flight, by airport size
| Group | All five causes | Carrier | Weather | Air traffic system | Security | Late aircraft |
|---|---|---|---|---|---|---|
| Largest third | 15.9 | 5.5 | 0.9 | 3.2 | 0.0 | 6.3 |
| Middle third | 14.2 | 4.4 | 0.6 | 2.9 | 0.0 | 6.2 |
| Smallest third | 14.1 | 4.5 | 0.6 | 3.0 | 0.0 | 5.9 |
Cause minutes of the airports of a group added up, over the completed flights of the same airports. Flights that arrived on time or under 15 minutes late carry no cause minutes.
Size against each cause, airport by airport
| Cause | Rank correlation with size | Reading |
|---|---|---|
| Carrier | 0.12 | weak, no direction |
| Weather | -0.03 | weak, no direction |
| Air traffic system | 0.00 | weak, no direction |
| Security | 0.20 | modest, higher at larger airports |
| Late aircraft | -0.04 | weak, no direction |
Spearman rank correlation between an airport’s scheduled departures and that cause’s share of its own delay minutes, across the airports in the groups. Zero is no relation and a value of one, positive or negative, is a perfect one.
Does size settle it
No cause lines up clearly with airport size. Weather is weak against size (-0.03) and late aircraft weak (-0.04), so the group figures above describe where the minutes fall, and an airport’s size says little about which cause dominates its delay.
What this does not show
Cause minutes belong to a flight’s arrival delay and are filed here under the airport it left from, so weather counted at an airport can have been met on the way or at the other end. The DOT takes the cause from the airline’s report, and late aircraft is a delay inherited from an earlier flight that may itself have started in weather. Groups are cut by rank of scheduled departures, not by a published airport class, and airports differ in airlines and routes as well as size. The report on airports where weather hurts most ranks each airport on its own.
Methodology
Calculated by FlyerIntel from 21,708,321 individual flight records in the US Department of Transportation Bureau of Transportation Statistics Reporting Carrier On-Time Performance dataset, covering July 2023 through July 2026. Following BTS methodology, a flight counts as delayed when it arrives 15 or more minutes after its scheduled arrival time. Cancelled and diverted flights have no arrival time and are excluded from on-time rates rather than counted as late; cancellation rates are reported separately. Full definitions are published at /methodology/. Delay minutes are the DOT’s cause minutes, which exist only for flights that arrived 15 or more minutes late, read from the departure rows of each covered airport with every year pooled. Airports need 5,000 scheduled departures to be included, are ordered by scheduled departures and cut into three groups of near equal count. Shares have the sum of the five cause columns of the same rows as their denominator.
Limitations
The source dataset covers scheduled domestic flights operated by carriers above the DOT reporting threshold; smaller carriers and international flights are not included. Flights sold under a mainline brand but flown by a regional carrier are attributed to the operating carrier, which is how the DOT records them. Past performance describes what has happened and is not a prediction about any individual flight. Cause attribution is reported by the airlines themselves.
Sources
- FlyerIntel analysis — FlyerIntel · source
- Reporting Carrier On-Time Performance — US Department of Transportation, Bureau of Transportation Statistics · source
Full FlyerIntel methodology · Report a problem with this analysis