{
  "name": "Airline Accountability Index — US domestic on-time performance by cause",
  "version": "2026-05",
  "methodology_version": "1.0.0",
  "license": "https://creativecommons.org/publicdomain/zero/1.0/",
  "license_note": "This derived aggregation is dedicated to the public domain under CC0 1.0: copy, modify and redistribute it, commercially or not, without permission or attribution. Citation is requested as a courtesy, not required. The dedication covers this data only — not the prose, code or design of travelaidnow.com, and not the Travelaidnow name.",
  "source_license": "https://www.usa.gov/government-works",
  "source_license_note": "The underlying BTS filings are works of the US Government and carry no copyright under 17 U.S.C. §105. That is their status, not a licence we grant.",
  "reporting_period": {
    "month": "2026-05",
    "label": "May 2026"
  },
  "source": {
    "name": "Reporting Carrier On-Time Performance (1987-present)",
    "url": "https://www.transtats.bts.gov/ontime/",
    "retrieved": "2026-07-28",
    "authority": "US DOT Bureau of Transportation Statistics"
  },
  "generated_at": "2026-07-28",
  "row_count": 7,
  "columns": [
    {
      "column": "carrier_iata",
      "type": "string",
      "definition": "IATA carrier code as filed with BTS."
    },
    {
      "column": "carrier_name",
      "type": "string",
      "definition": "Marketing name of the reporting carrier."
    },
    {
      "column": "flights",
      "type": "integer",
      "definition": "Scheduled domestic flights the carrier filed in the reporting period. The denominator for every rate in this file."
    },
    {
      "column": "arrivals_late_over_15_min",
      "type": "integer",
      "definition": "Flights arriving more than 15 minutes after scheduled arrival. Cancelled and diverted flights are not counted as late."
    },
    {
      "column": "late_pct",
      "type": "decimal",
      "definition": "arrivals_late_over_15_min / flights, as a percentage to one decimal place."
    },
    {
      "column": "cancellations",
      "type": "integer",
      "definition": "Flights cancelled, as filed."
    },
    {
      "column": "cancelled_pct",
      "type": "decimal",
      "definition": "cancellations / flights, as a percentage to one decimal place."
    },
    {
      "column": "diversions",
      "type": "integer",
      "definition": "Flights diverted to an airport other than the scheduled destination."
    },
    {
      "column": "total_arrival_delay_minutes",
      "type": "integer",
      "definition": "Sum of arrival delay in minutes across all flights. Early arrivals count as zero rather than as negative minutes, which would flatter the mean."
    },
    {
      "column": "mean_arrival_delay_minutes",
      "type": "decimal",
      "definition": "total_arrival_delay_minutes / flights. Includes on-time flights as zero, so this is not the mean delay of delayed flights."
    },
    {
      "column": "reported_delay_minutes",
      "type": "integer",
      "definition": "Sum of the five filed delay causes. Smaller than total_arrival_delay_minutes, because a cause is only filed for flights delayed 15 minutes or more. This is the denominator for every *_share_pct column."
    },
    {
      "column": "carrier_delay_minutes",
      "type": "integer",
      "definition": "Delay minutes coded to circumstances within the carrier's control — crew, maintenance, fuelling, baggage loading."
    },
    {
      "column": "late_aircraft_delay_minutes",
      "type": "integer",
      "definition": "Delay minutes coded to the inbound aircraft arriving late from a previous leg."
    },
    {
      "column": "nas_delay_minutes",
      "type": "integer",
      "definition": "Delay minutes coded to the National Airspace System: air-traffic volume, airport operations, and non-extreme weather handled through traffic management."
    },
    {
      "column": "weather_delay_minutes",
      "type": "integer",
      "definition": "Delay minutes coded to extreme weather only. Weather that is managed through air-traffic flow control is filed under NAS, so this column understates all weather-driven delay."
    },
    {
      "column": "security_delay_minutes",
      "type": "integer",
      "definition": "Delay minutes coded to security screening, terminal evacuation or a breach."
    },
    {
      "column": "carrier_delay_share_pct",
      "type": "decimal",
      "definition": "carrier_delay_minutes / reported_delay_minutes, as a percentage."
    },
    {
      "column": "late_aircraft_delay_share_pct",
      "type": "decimal",
      "definition": "late_aircraft_delay_minutes / reported_delay_minutes, as a percentage."
    },
    {
      "column": "nas_delay_share_pct",
      "type": "decimal",
      "definition": "nas_delay_minutes / reported_delay_minutes, as a percentage."
    },
    {
      "column": "weather_delay_share_pct",
      "type": "decimal",
      "definition": "weather_delay_minutes / reported_delay_minutes, as a percentage."
    },
    {
      "column": "security_delay_share_pct",
      "type": "decimal",
      "definition": "security_delay_minutes / reported_delay_minutes, as a percentage."
    },
    {
      "column": "carrier_plus_late_aircraft_delay_share_pct",
      "type": "decimal",
      "definition": "The two filed categories carrier_delay_minutes and late_aircraft_delay_minutes, summed and divided by reported_delay_minutes. THIS SUM IS OURS, NOT A BTS FIELD. It establishes no cause and no fault: late-arriving aircraft records that the inbound aircraft was late, not what delayed it, so an unknown part of it began as weather or traffic flow earlier in the day. Both components are published separately so the sum can be rejected."
    }
  ],
  "limitations": [
    "Domestic US scheduled service only. 14 CFR part 234 requires reporting from US carriers above 0.5% of domestic scheduled-service passenger revenue, and covers domestic service. No international flight appears in this file.",
    "It therefore says nothing about any US-Mexico route, and nothing at all about Volaris, Viva Aerobus or Aeroméxico. Mexican carrier performance comes from AFAC, a separate source not published here.",
    "One reporting month, carrying that month's seasonality. A snapshot, not a trend.",
    "Only carriers required to report appear. A hub served largely by non-reporting regional carriers will read better here than a traveller experiences.",
    "Delay-cause shares exclude flights delayed under 15 minutes, for which no cause is filed.",
    "'Weather' means extreme weather as BTS defines it. Weather managed through air-traffic flow control is filed under NAS, so weather's true contribution is higher than the weather column alone.",
    "carrier_plus_late_aircraft_delay_share_pct sums two BTS fields; the sum is ours, not a federal statistic, and it establishes no fault."
  ],
  "reproduce": [
    "Download the Reporting Carrier On-Time Performance file for May 2026 from https://www.transtats.bts.gov/ontime/.",
    "Keep rows for the reporting carriers listed in this file; no other filtering is applied.",
    "Group by reporting carrier and sum: flights, arrivals more than 15 minutes late, cancellations, diversions, arrival delay minutes, and the five filed delay-cause minute columns.",
    "Rates divide by flights. Cause shares divide by the sum of the five cause columns, not by total arrival delay minutes.",
    "Round every published figure to one decimal place, half away from zero.",
    "carrier_plus_late_aircraft_delay_share_pct sums the carrier and late-aircraft minutes before dividing, rather than adding the two rounded shares."
  ],
  "totals": {
    "carriers": 7,
    "flights": 442954,
    "arrivals_late_over_15_min": 97189,
    "cancellations": 3579,
    "late_pct": 21.9,
    "cancelled_pct": 0.8,
    "reported_delay_minutes": 6220554,
    "carrier_delay_share_pct": 32.1,
    "late_aircraft_delay_share_pct": 43.1,
    "nas_delay_share_pct": 20.5,
    "weather_delay_share_pct": 4.1,
    "security_delay_share_pct": 0.1,
    "carrier_plus_late_aircraft_delay_share_pct": 75.2
  },
  "carriers": [
    {
      "carrier_iata": "WN",
      "carrier_name": "Southwest Airlines",
      "flights": 120646,
      "arrivals_late_over_15_min": 33126,
      "late_pct": 27.5,
      "cancellations": 474,
      "cancelled_pct": 0.4,
      "diversions": 320,
      "total_arrival_delay_minutes": 1884783,
      "mean_arrival_delay_minutes": 15.6,
      "reported_delay_minutes": 1724859,
      "carrier_delay_minutes": 514486,
      "late_aircraft_delay_minutes": 885363,
      "nas_delay_minutes": 281515,
      "weather_delay_minutes": 39256,
      "security_delay_minutes": 4239,
      "carrier_delay_share_pct": 29.8,
      "late_aircraft_delay_share_pct": 51.3,
      "nas_delay_share_pct": 16.3,
      "weather_delay_share_pct": 2.3,
      "security_delay_share_pct": 0.2,
      "carrier_plus_late_aircraft_delay_share_pct": 81.2
    },
    {
      "carrier_iata": "F9",
      "carrier_name": "Frontier Airlines",
      "flights": 18423,
      "arrivals_late_over_15_min": 4268,
      "late_pct": 23.2,
      "cancellations": 95,
      "cancelled_pct": 0.5,
      "diversions": 39,
      "total_arrival_delay_minutes": 345494,
      "mean_arrival_delay_minutes": 18.8,
      "reported_delay_minutes": 328501,
      "carrier_delay_minutes": 77033,
      "late_aircraft_delay_minutes": 172306,
      "nas_delay_minutes": 71444,
      "weather_delay_minutes": 7718,
      "security_delay_minutes": 0,
      "carrier_delay_share_pct": 23.4,
      "late_aircraft_delay_share_pct": 52.5,
      "nas_delay_share_pct": 21.7,
      "weather_delay_share_pct": 2.3,
      "security_delay_share_pct": 0,
      "carrier_plus_late_aircraft_delay_share_pct": 75.9
    },
    {
      "carrier_iata": "AA",
      "carrier_name": "American Airlines",
      "flights": 88740,
      "arrivals_late_over_15_min": 20427,
      "late_pct": 23,
      "cancellations": 1324,
      "cancelled_pct": 1.5,
      "diversions": 367,
      "total_arrival_delay_minutes": 1770798,
      "mean_arrival_delay_minutes": 20,
      "reported_delay_minutes": 1689635,
      "carrier_delay_minutes": 556350,
      "late_aircraft_delay_minutes": 779682,
      "nas_delay_minutes": 231956,
      "weather_delay_minutes": 119637,
      "security_delay_minutes": 2010,
      "carrier_delay_share_pct": 32.9,
      "late_aircraft_delay_share_pct": 46.1,
      "nas_delay_share_pct": 13.7,
      "weather_delay_share_pct": 7.1,
      "security_delay_share_pct": 0.1,
      "carrier_plus_late_aircraft_delay_share_pct": 79.1
    },
    {
      "carrier_iata": "UA",
      "carrier_name": "United Airlines",
      "flights": 74200,
      "arrivals_late_over_15_min": 14733,
      "late_pct": 19.9,
      "cancellations": 286,
      "cancelled_pct": 0.4,
      "diversions": 216,
      "total_arrival_delay_minutes": 1045262,
      "mean_arrival_delay_minutes": 14.1,
      "reported_delay_minutes": 974542,
      "carrier_delay_minutes": 237329,
      "late_aircraft_delay_minutes": 367325,
      "nas_delay_minutes": 331868,
      "weather_delay_minutes": 37748,
      "security_delay_minutes": 272,
      "carrier_delay_share_pct": 24.4,
      "late_aircraft_delay_share_pct": 37.7,
      "nas_delay_share_pct": 34.1,
      "weather_delay_share_pct": 3.9,
      "security_delay_share_pct": 0,
      "carrier_plus_late_aircraft_delay_share_pct": 62
    },
    {
      "carrier_iata": "B6",
      "carrier_name": "JetBlue Airways",
      "flights": 19806,
      "arrivals_late_over_15_min": 3671,
      "late_pct": 18.5,
      "cancellations": 42,
      "cancelled_pct": 0.2,
      "diversions": 49,
      "total_arrival_delay_minutes": 251459,
      "mean_arrival_delay_minutes": 12.7,
      "reported_delay_minutes": 232866,
      "carrier_delay_minutes": 61330,
      "late_aircraft_delay_minutes": 99901,
      "nas_delay_minutes": 65360,
      "weather_delay_minutes": 5996,
      "security_delay_minutes": 279,
      "carrier_delay_share_pct": 26.3,
      "late_aircraft_delay_share_pct": 42.9,
      "nas_delay_share_pct": 28.1,
      "weather_delay_share_pct": 2.6,
      "security_delay_share_pct": 0.1,
      "carrier_plus_late_aircraft_delay_share_pct": 69.2
    },
    {
      "carrier_iata": "DL",
      "carrier_name": "Delta Air Lines",
      "flights": 91955,
      "arrivals_late_over_15_min": 16099,
      "late_pct": 17.5,
      "cancellations": 1144,
      "cancelled_pct": 1.2,
      "diversions": 236,
      "total_arrival_delay_minutes": 1121085,
      "mean_arrival_delay_minutes": 12.2,
      "reported_delay_minutes": 1038913,
      "carrier_delay_minutes": 474260,
      "late_aircraft_delay_minutes": 291697,
      "nas_delay_minutes": 238054,
      "weather_delay_minutes": 33675,
      "security_delay_minutes": 1227,
      "carrier_delay_share_pct": 45.6,
      "late_aircraft_delay_share_pct": 28.1,
      "nas_delay_share_pct": 22.9,
      "weather_delay_share_pct": 3.2,
      "security_delay_share_pct": 0.1,
      "carrier_plus_late_aircraft_delay_share_pct": 73.7
    },
    {
      "carrier_iata": "AS",
      "carrier_name": "Alaska Airlines",
      "flights": 29184,
      "arrivals_late_over_15_min": 4865,
      "late_pct": 16.7,
      "cancellations": 214,
      "cancelled_pct": 0.7,
      "diversions": 54,
      "total_arrival_delay_minutes": 265892,
      "mean_arrival_delay_minutes": 9.1,
      "reported_delay_minutes": 231238,
      "carrier_delay_minutes": 77827,
      "late_aircraft_delay_minutes": 85185,
      "nas_delay_minutes": 57722,
      "weather_delay_minutes": 9709,
      "security_delay_minutes": 795,
      "carrier_delay_share_pct": 33.7,
      "late_aircraft_delay_share_pct": 36.8,
      "nas_delay_share_pct": 25,
      "weather_delay_share_pct": 4.2,
      "security_delay_share_pct": 0.3,
      "carrier_plus_late_aircraft_delay_share_pct": 70.5
    }
  ]
}