How to read cancellation data
A cancelled flight is the clearest failure in the airline record, and it is easy to misread. The count rests on a definition with a seven-day condition in it, and the cause is the airline’s own filing. This guide covers what the DOT counts, how the four cause codes work, and how rates move by month and weekday.
What counts as a cancelled flight
Under 14 CFR 234.2 a cancelled flight is one that was not operated but was listed in the airline’s reservation system within seven calendar days of its scheduled departure. A flight dropped from the system earlier than that is a discontinued flight, and the rule tells airlines not to report those (234.4). So a cancellation statistic describes late changes to the schedule.
FlyerIntel counts a cancelled flight once, at the airport it was scheduled to leave, and divides by all scheduled flights from that airport to get the cancellation rate. Over July 2023 – July 2026, 265,507 of 17,884,589 scheduled departures were cancelled, 1.48%, or 1 in 67. A cancelled flight has no arrival time, so it is outside the on-time rate (see the guide to how on-time performance is counted). The data does not say whether passengers were rebooked or told in advance.
Cancelled or diverted
A diverted flight was operated to a point other than its scheduled destination. In the rule’s example, a schedule of A to B to C that is flown as A to C makes the A to B segment diverted and the B to C segment cancelled. A diversion is not a delay. The aircraft lands somewhere else, so there is no arrival time at the scheduled destination and the flight is left out of the on-time rate. In this period 47,023 departures were diverted, 0.26% of those scheduled, against 1.48% cancelled. The report on where flights do not land counts diversions at the arrival airport, so its totals differ.
The four cause codes
Airlines file one code with every cancelled flight (14 CFR 234.4). In the rule’s terms:
- A, Air Carrier. Circumstances within the airline’s control. The rule’s examples are a lack of flight crew and maintenance.
- B, Extreme weather. Significant weather, actual or forecast, at departure, en route or at arrival, that prevents the flight under the regulatory standards or in the airline’s judgment.
- C, National Aviation System. Conditions inside the air traffic system: non-extreme weather, airport operations, heavy traffic volume and air traffic control.
- D, Security. Malfunctioning screening equipment, a breach that forces an evacuation, or the need to re-screen passengers.
Weather appears in two of the four, so code B understates what weather does. The code is also the airline’s own filing and not a finding of fault. The report on why airlines cancel found that the airline putting the largest share of its cancellations on itself did not cancel more often than the one putting the smallest share, so it does not rank carriers by their codes. The methodology page states the same limit.
A DOT rule published on September 3, 2026 (91 FR 56588) takes ten kinds of event out of the Air Carrier category and gives them a category of their own, for cancellations as for delays. DOT postponed its effective date to February 1, 2027 (notice of October 15, 2026), so the figures here use the four codes above.
Why flights were cancelled
Every cancelled departure in the period carried one of the four codes. The shares below are of the 265,507 coded cancellations at the covered airports. The report on why airlines cancel counts by airline, so its totals differ.
| Code | Cause | Cancelled flights | Share |
|---|---|---|---|
| A | Air Carrier | 68,590 | 25.8% |
| B | Extreme weather | 158,058 | 59.5% |
| C | National Aviation System | 38,759 | 14.6% |
| D | Security | 100 | <0.1% |
Extreme weather is the largest code and Air Carrier the second largest. The National Aviation System code also takes in weather that is not extreme, so the weather in these shares is understated.
By month
The three months with the highest rates, January, July and August, held 48.6% of the cancellations on 27.4% of the flights. January had the highest rate, 3.78%, and October the lowest, 0.62%.
| Month | Years in the data | Scheduled flights | Cancelled | Rate |
|---|---|---|---|---|
| January | 3 | 1,343,722 | 50,743 | 3.78% |
| February | 3 | 1,266,574 | 17,410 | 1.37% |
| March | 3 | 1,484,847 | 23,459 | 1.58% |
| April | 3 | 1,455,724 | 11,084 | 0.76% |
| May | 3 | 1,508,124 | 16,179 | 1.07% |
| June | 3 | 1,499,598 | 22,277 | 1.49% |
| July | 4 | 2,050,076 | 54,623 | 2.66% |
| August | 3 | 1,502,242 | 23,755 | 1.58% |
| September | 3 | 1,416,475 | 11,117 | 0.78% |
| October | 3 | 1,504,385 | 9,304 | 0.62% |
| November | 3 | 1,414,742 | 13,780 | 0.97% |
| December | 3 | 1,438,080 | 11,776 | 0.82% |
Each row adds up every year of that month in the period, so a month in more years has more flights. July appears in 4 years and the others in fewer, because the period starts and ends in July. The research on which months cancel the most flights shows each year and month on its own.
By weekday
By scheduled weekday, Wednesday had the lowest cancellation rate at 1.11% and Sunday the highest at 2.01%. The report on the weekday that cancels the fewest flights found the same weekday lowest in the largest, middle and smallest thirds of airports by size.
In week order the rates were Monday 1.74%, Tuesday 1.35%, Wednesday 1.11%, Thursday 1.25%, Friday 1.45%, Saturday 1.43%, Sunday 2.01%.
Reading a rate with care
- Cancellations come in clusters. In FlyerIntel’s day-by-day analysis, nobody flies on an average day, the worst tenth of each airport’s days carried most of the cancellations, so an average rate says little about an ordinary day.
- A cancellation is attributed to the airport the flight was to leave. The weather behind it may have been at the other end, on the route, or somewhere the aircraft was meant to come from.
- Airport and airline pages show their own rates and cause splits once enough flights stand behind them, as in the cancellations section of the Atlanta page. The refund checker covers a flight you booked that was cancelled, and the glossary defines each term used here.
What this is based on
The totals are for departures from the 64 covered airports, July 2023 – July 2026, added up from the same airport records that fill the airport pages. A cancellation is counted once, at the airport the flight was scheduled to leave.
- US Department of Transportation, 14 CFR Part 234, Airline Service Quality Performance Reports Sections 234.2 (definitions) and 234.4 (what carriers report, and the cause codes).
- Bureau of Transportation Statistics, Reporting Carrier On-Time Performance, field list The fields of the file FlyerIntel reads, including the 15-minute arrival indicator and the five delay-cause minutes.
- Federal Register, 91 FR 56588, Cause of Airline Delay and Cancellation Categories Under Section 511(b) of the FAA Reauthorization Act of 2024 Published September 3, 2026.
- Federal Register, Cause of Airline Delay and Cancellation Categories Under Section 511(b) of the FAA Reauthorization Act of 2024; Delay of Effective Date Published October 15, 2026; moves the effective date of the September 3 rule to February 1, 2027.
An error in a figure or a definition can be reported on the corrections page. How FlyerIntel decides what to publish is set out in the editorial policy.
More guides
- How on-time performance is counted. The 15-minute rule, scheduled against actual times, and what happens to cancelled and diverted flights.
- Why flights are delayed: the five DOT causes. The five causes airlines report, what a late aircraft is, and where the delay minutes went.
- How to read an airport’s reliability profile. What each section of an airport page means, and how to compare airports without fooling yourself.
- Choosing a flight to avoid delays. Hour, day, airport, route and connection: what the record says to check, in order.
- What to know about connections and layovers. Minimum connection time, how a delay reaches the next flight, and the layovers the arrival record supports.
- Glossary. Plain definitions of the terms the guides and the site use.