FlyerIntel

Glossary

The terms below appear on the airport, route, airline and flight pages, in the research reports and in the guides. Each is defined as the site uses it, in line with the methodology page, and the DOT’s own terms follow 14 CFR Part 234. After each definition are the pages where the term is used or explained.

Terms, A to Z

90th-percentile delay
The arrival delay that nine in ten flights on a route came in at or under. The worst tenth landed at least this late, so it shows how bad the bad days get without being set by the single worst one. Used in: Connection checker
Air Carrier delay
A delay the airline assigns to circumstances within its own control. It is one of the five delay causes in 14 CFR 234.4 and is the airline’s own filing, not an outside finding. Used in: The five delay causes · Methodology
Arrival delay
The minutes between a flight’s scheduled arrival and the time its aircraft reached the gate. A negative value means the flight arrived early. The on-time rate, the severe delay rate and the connection checker all start from it. Used in: Scheduled against actual time · Connection checker
Block time
The time an airline schedules between leaving the gate and reaching the gate at the other end. It includes taxiing at both airports, which is why a flight can taxi for a long time and still arrive early. Used in: Taxi time, the ground tax · Making up time in the air
Cancellation code
The letter an airline files with each cancelled flight: A for Air Carrier, B for extreme weather, C for the National Aviation System and D for security. The operating airline chooses it, so it records the reason the airline gave and not an independent finding. Used in: The four codes · Why airlines cancel
Cancelled flight
A flight that was not operated but was listed in the airline’s reservation system within seven calendar days of its scheduled departure (14 CFR 234.2). FlyerIntel counts it once, at the airport it was scheduled to leave, and the cancellation rate is cancelled flights divided by scheduled flights. Used in: What counts as cancelled · Methodology
Completed flight
A flight that operated and has a recorded arrival delay. Cancelled and diverted flights are not completed flights, and the on-time rate is calculated over completed flights only. Used in: Methodology · Cancelled and diverted flights
Covered airport
One of the major US passenger airports that FlyerIntel measures and gives a page. Network totals and comparisons in the guides and research add up flights at covered airports only. Used in: All covered airports · Limitations
Departure window
One of the six blocks of the day used to group flights by scheduled local departure time: 5–9 AM, 9 AM–12 PM, 12–3 PM, 3–6 PM, 6–9 PM and 9 PM–5 AM. The same hours are used for scheduled arrival windows on the connection checker. Used in: Methodology · When to fly
Discontinued flight
A flight dropped from the airline’s reservation system more than seven calendar days before its scheduled departure (14 CFR 234.2). Airlines do not report discontinued flights, so they never count as cancellations. Used in: What counts as cancelled
Diverted flight
A flight that was operated to an airport other than its scheduled destination (14 CFR 234.2). It never arrives at the scheduled destination, so it has no arrival delay there and is left out of the on-time rate. Used in: Cancelled or diverted · Where flights do not land
Extreme weather
The DOT cause code for weather the airline judges to prevent a flight from operating, actual or forecast. Ordinary weather that slows traffic is filed under the National Aviation System instead, so this category understates what weather costs. Used in: The five delay causes · What weather costs each airport
Late-arriving aircraft
The delay cause for a flight held up because the aircraft arrived late from its previous flight. It records how the delay reached the flight and not why the earlier flight was late. Used in: What the code means · What a late aircraft costs the next flight
Layover
The time between the scheduled arrival of the flight bringing a traveler in and the scheduled departure of the next one. The connection checker subtracts the time needed from it to find how much delay the first flight can have. Used in: Connections and layovers · Connection checker
Median arrival delay
The middle arrival delay among completed flights: half arrived with less delay and half with more. A negative median means the typical flight landed early, and a few extreme days do not move it as they move an average. Used in: Methodology · How on-time performance is counted
Minimum connection time
The shortest gap that a booking system will sell between two flights at an airport. It is a scheduling setting, not a measure of how long a connection takes, and it does not appear in the DOT data FlyerIntel uses. Used in: Connections and layovers · Best airports for a tight connection
National Aviation System (NAS) delay
A delay the airline assigns to conditions inside the air traffic system: non-extreme weather, airport operations, heavy traffic volume and air traffic control. It is a broad category and does not point to a single party. Used in: The five delay causes · Rankings
On time
Arriving at the gate less than 15 minutes after the scheduled arrival time, or earlier. The on-time rate is on-time arrivals divided by completed flights, so it leaves out cancelled and diverted flights. Used in: The 15-minute rule · Methodology
Reliability score
A 0 to 100 summary of how dependably an airport, route or airline performed, where higher is better. It combines several measures, cancellations among them, using fixed weights listed on the methodology page. Used in: Methodology · Reading an airport profile
Reporting carrier
An airline required to file on-time reports with the DOT. For flights since 2018 the rule sets the line at 0.5 percent of domestic scheduled passenger revenue (14 CFR 234.2). A flight is attributed to the carrier that operated it, so a regional airline flying under a mainline brand is listed under its own name. Used in: Limitations · Airlines
Sample floor
The smallest number of flights that must stand behind a figure before FlyerIntel publishes it. The floors include 5,000 flights for an airport, 750 for a route, 10,000 for an airline and 120 for any hour, weekday or month, and 500 cancellations for a cause split. Below its floor a section is left out. Used in: Sample-size thresholds
Scheduled arrival
The arrival time the airline published for the date of the flight, in the destination airport’s local time. A flight’s delay is measured against it, and the connection checker groups flights by its hour. Used in: Scheduled against actual time · Connection checker
Scheduled departure
The departure time the airline published for the date of the flight, in the origin airport’s local time. FlyerIntel groups flights by it and not by the actual departure, because the scheduled time is what a traveler chooses when booking. Used in: Methodology · Choosing the hour
Security
The DOT cause code for delays and cancellations from malfunctioning screening equipment, a security breach that forces an evacuation, or the need to re-screen passengers. It accounts for a very small share of both. Used in: The five delay causes · The four cancellation codes
Severe delay
An arrival 60 or more minutes late. The severe delay rate is those arrivals divided by completed flights, and it is the size of delay that can end a connection. Used in: Methodology · Best airports for a tight connection
Taxi-in
The time between an aircraft touching down and reaching its gate, as the airline reports it. It is inside the arrival delay already, so the connection checker does not subtract it a second time. Used in: Taxi time, the ground tax · Wheels down, still late
Taxi-out
The time between an aircraft leaving the gate and lifting off, as the airline reports it. It counts toward the scheduled block time and is not itself a delay. Used in: Taxi time, the ground tax · Airport profile sections
Time needed
The minutes a traveler needs after the aircraft reaches the gate to leave it and be ready for the next flight. The connection checker assumes 30 unless told otherwise. It is an assumption, because the data has no gate or terminal information. Used in: Connection checker · Reading the checker
Turnaround
The time an aircraft spends on the ground at an airport between one flight and the next, with overnight stays left out. A short scheduled turnaround leaves little room to recover from a late arrival. Used in: How fast an aircraft turns · What a late aircraft costs the next flight

What this is based on

The DOT terms are taken from 14 CFR Part 234, Airline Service Quality Performance Reports (sections 234.2 and 234.4), and the field names behind the taxi and delay figures from the Bureau of Transportation Statistics field list. The other terms are FlyerIntel’s own and are defined where the figures are calculated, on the methodology page. An error in a definition can be reported on the corrections page.