Almost every US flight statistic you read — the on-time percentages on our route pages and airport pages, the headlines about the worst airline for delays — ultimately traces to one source: the Bureau of Transportation Statistics (BTS), part of the US Department of Transportation. Understanding how BTS collects and defines its data tells you exactly how much to trust it, and where its blind spots are.
Who collects the data, and how?
BTS runs the Airline Service Quality Performance (ASQP) program. Larger US airlines are required to report flight-by-flight data every month for their domestic scheduled service, including:
- The scheduled gate departure and arrival times.
- The actual gate-out, wheels-off, wheels-on and gate-in times.
- Whether the flight was cancelled or diverted.
- The number of minutes attributable to each delay cause, when a flight arrives 15+ minutes late.
BTS aggregates these monthly submissions into the public tables and the searchable On-Time Performance database. Because the federal government produces it, the data is public domain — free to use and verify.
What counts as “on-time”?
BTS uses a single, consistent threshold. A flight is on-time if it arrives at the gate fewer than 15 minutes after its scheduled arrival and is not cancelled or diverted. The same 15-minute rule applies to departures. This is the definition we use site-wide — see what ‘on-time’ really means for why that 15-minute window matters more than it sounds.
| Field BTS publishes | What it means |
|---|---|
| On-time arrival % | Share of operated flights arriving within 15 min of schedule |
| On-time departure % | Same threshold, measured at the origin gate |
| Cancellation % | Share of scheduled flights that did not operate |
| Diversion % | Flights that landed somewhere other than the destination |
| Average delay | Usually reported among delayed flights, in minutes |
| Delay causes | Minutes split across five categories (below) |
The five delay-cause categories
When a flight is 15+ minutes late, the reporting airline assigns the delay minutes to one of five buckets — the framework we unpack in US flight delay causes explained:
- Air-carrier delay — within the airline’s control (maintenance, crew, baggage, fueling).
- Extreme weather — significant weather that prevents operation.
- National Airspace System (NAS) delay — air-traffic control, airport-operations and non-extreme weather that the FAA manages.
- Late-arriving aircraft — the inbound plane arrived late, delaying this flight. The largest single category network-wide.
- Security delay — security-related evacuations or screening issues.
A crucial subtlety: the airline assigns the cause itself. The split between “weather” and “NAS” or “late-arriving aircraft” is a reported judgment, not an independent measurement — worth remembering when you read cause breakdowns.
What BTS data does not capture
The dataset is authoritative, but it has real limits — which is why we label our route figures as estimates in the methodology:
- Only reporting carriers. Historically, airlines above roughly 0.5% of domestic scheduled passenger revenue must report. Smaller carriers and some regional operations may be excluded or folded into a mainline partner. Foreign carriers’ US flights are not in the core domestic dataset.
- Airline-set schedules. On-time is measured against the airline’s own published schedule. A carrier that pads its schedule clears the 15-minute bar more easily without actually flying faster.
- It lags. BTS data is monthly and delayed, usually published a month or two after the fact. It is a historical record, not a live feed — for real-time status you need a flight tracker.
- No per-route consumer table. BTS publishes by carrier and by airport, but specific origin–destination on-time rates are not broken out in the standard consumer tables. That is why our per-route figures are estimates derived from the endpoint airports’ BTS performance, clearly labelled as such.
How RouteOnTime uses BTS data
We take the real, full-year 2024 BTS figures for hub airports — on-time departure and arrival rates, cancellation rates, and average delay among delayed flights — and present them on the airport pages. For routes, where no published per-pair table exists, we derive estimates from the origin and destination airports’ reliability and label them plainly. Every figure carries a “data as of” date and links back to the primary BTS source so you can verify it yourself. The full process and its limitations live on our methodology page.
The bottom line
BTS on-time data is the gold standard public record for US flight reliability: consistent, free, and comprehensive across reporting carriers. But it covers only those carriers, judges punctuality against airline-set schedules, lags by a month or more, and does not publish per-route rates — so read it as a strong historical signal, not a real-time guarantee. With those caveats in mind, dig into the routes and airports you fly.