Glossary
Each term has one meaning on this site. The first text is a plain explanation. The quotation is the text of BTS, with a link to the page.
Last checked against the BTS pages:
- On time
A flight is on time when it arrives less than 15 minutes after its scheduled arrival time. A flight that arrives 15 minutes late or more is late.
The words of BTS:
Arrival delay equals the difference of the actual arrival time minus the scheduled arrival time. A flight is considered on-time when it arrives less than 15 minutes after its published arrival time.
BTS, Airline On-Time Performance Data (data profile), entry "Arrival Delay"The flights that arrived on time, divided by all scheduled flights, in percent. A cancelled flight and a diverted flight are not on time. The site uses this share on route, airline and ranking pages.
BTS has no entry for this term. The explanation is the own text of the site.
- Left on time
A flight left on time when it left the gate less than 15 minutes after its scheduled departure time. Airport pages show the share of departures that left on time.
The words of BTS:
A flight arriving or departing 15 minutes or more after the scheduled time.
BTS, Airline On-Time Performance Data (data profile), entry "Late Flight"- Cancelled
A flight that was in the reservation system of the airline in the seven days before its scheduled departure and did not operate.
The words of BTS:
A flight that was listed in a carrier's computer reservation system during the seven calendar days prior to scheduled departure but was not operated.
BTS, Airline On-Time Performance Data (data profile), entry "Cancelled Flight"- Diverted
A flight that landed at an airport other than the airport on its schedule.
The words of BTS:
A flight that is required to land at a destination other than the original scheduled destination for reasons beyond the control of the pilot/company.
BTS, Airline On-Time Performance Data (data profile), entry "Diverted Flight"- Average arrival delay
The mean of actual arrival time minus scheduled arrival time, in minutes, for flights that arrived. An early flight counts as a negative number. A table that says "late minutes only" counts an early flight as zero.
The words of BTS:
Difference in minutes between scheduled and actual arrival time. Early arrivals set to 0.
BTS, Reporting Carrier On-Time Performance, field ArrDelayMinutes- Reporting carrier
An airline that sends on-time data to BTS for the flights that it operates. An airline with at least 0.5 percent of domestic scheduled passenger revenue reports. Some other airlines report by choice. The rest are not in the files.
The words of BTS:
Reporting carriers are required to (or voluntarily) report on-time data for flights they operate: on-time arrival and departure data for non-stop domestic flights by month and year, by carrier and by origin and destination airport.
BTS, Reporting Carrier On-Time Performance, field Reporting_Airline- Marketing carrier and operating carrier
The marketing carrier sells the ticket. The operating carrier flies the aircraft. A regional airline can operate a flight that a larger airline sells. This site shows the operating carrier.
The words of BTS:
Marketing carriers market flights for themselves and, in some cases, for regional code share partners.
BTS, Airline On-Time Performance Data (data profile), table "Marketing Carrier On-Time Performance"- BTS carrier code
The short code that BTS gives to a carrier, for example DL. The site shows the code beside the name of each airline.
The words of BTS:
Code assigned by IATA and commonly used to identify a carrier. As the same code may have been assigned to different carriers over time, the code is not always unique.
BTS, Airline On-Time Performance Data (data profile), entry "Carrier Code"- Scheduled departure hour
The hour of the scheduled departure time in the reservation system, in local time at the departure airport. The hour row on each page groups flights by this hour.
The words of BTS:
CRS Departure Time Block, Hourly Intervals
BTS, Reporting Carrier On-Time Performance, field DepTimeBlk- City market
A group of airports that serve one city. BTS gives each group one number. The site uses it to link the routes between the same two cities.
The words of BTS:
An identification number assigned by US DOT to identify a city market. Use this field to consolidate airports serving the same city market.
BTS, Airline On-Time Performance Data (data profile), entry "City Market ID"- Air carrier (delay cause)
A BTS category of delay. The cause was in the control of the airline.
The words of BTS:
Air Carrier: The cause of the cancellation or delay was due to circumstances within the airline's control (e.g. maintenance or crew problems, aircraft cleaning, baggage loading, fueling, etc.).
BTS, Understanding the Reporting of Causes of Flight Delays and Cancellations (Read in the Internet Archive copy of 19 September 2026, because bts.gov refuses a script.)- Late-arriving aircraft (delay cause)
A BTS category of delay. The aircraft of the flight came late from its earlier flight. BTS does not record the cause of the earlier delay in this category.
The words of BTS:
Late-arriving aircraft: A previous flight with same aircraft arrived late, causing the present flight to depart late.
BTS, Understanding the Reporting of Causes of Flight Delays and Cancellations (Read in the Internet Archive copy of 19 September 2026, because bts.gov refuses a script.)- National Aviation System, NAS (delay cause)
A BTS category of delay. It covers air traffic control, airport operations, heavy traffic and weather that is not extreme.
The words of BTS:
National Aviation System (NAS): Delays and cancellations attributable to the national aviation system that refer to a broad set of conditions, such as non-extreme weather conditions, airport operations, heavy traffic volume, and air traffic control.
BTS, Understanding the Reporting of Causes of Flight Delays and Cancellations (Read in the Internet Archive copy of 19 September 2026, because bts.gov refuses a script.)- Extreme weather (delay cause)
A BTS category of delay. The airline judged that severe weather delayed or stopped the flight. Other weather is in the NAS category.
The words of BTS:
Extreme Weather: Significant meteorological conditions (actual or forecasted) that, in the judgment of the carrier, delays or prevents the operation of a flight such as tornado, blizzard or hurricane.
BTS, Understanding the Reporting of Causes of Flight Delays and Cancellations (Read in the Internet Archive copy of 19 September 2026, because bts.gov refuses a script.)- Security (delay cause)
A BTS category of delay. It covers a terminal evacuation, a new boarding after a security breach, broken screening equipment and long screening lines.
The words of BTS:
Security: Delays or cancellations caused by evacuation of a terminal or concourse, re-boarding of aircraft because of security breach, inoperative screening equipment and/or long lines in excess of 29 minutes at screening areas.
BTS, Understanding the Reporting of Causes of Flight Delays and Cancellations (Read in the Internet Archive copy of 19 September 2026, because bts.gov refuses a script.)- Delay minutes
For a flight that arrived 15 minutes late or more, the airline splits the late minutes across the five BTS categories. The site shows the share of the minutes for each category. It assigns no cause itself.
The words of BTS:
The airlines report the causes of delay in broad categories that were created by the Air Carrier On-Time Reporting Advisory Committee. The categories are Air Carrier, National Aviation System, Weather, Late-Arriving Aircraft and Security. The causes of cancellation are the same, except there is no late-arriving aircraft category.
BTS, Understanding the Reporting of Causes of Flight Delays and Cancellations (Read in the Internet Archive copy of 19 September 2026, because bts.gov refuses a script.)- Route
One direction between two airports. ORD to LGA and LGA to ORD are two routes. A route page covers the reporting airlines that flew the route.
BTS has no entry for this term. The explanation is the own text of the site.
- Latest 12 months
The 12 months of BTS data that end with the newest month on file. A page gives the first and last month. The previous 12 months are the 12 months before them.
BTS has no entry for this term. The explanation is the own text of the site.
- BTS release
The publication of one new month of on-time data by BTS. The site follows each release and records the figures that changed by 2.0 points or more.
BTS has no entry for this term. The explanation is the own text of the site.
The site copied the texts of BTS on . A quotation keeps the spelling of BTS.