Data Sources & Methodology
Primary Data Source
All flight delay statistics on AirDelay come from the Bureau of Transportation Statistics (BTS), a division of the US Department of Transportation. Specifically, we use the Airline On-Time Performance Data (also known as the "On-Time Reporting Carrier On-Time Performance" dataset).
What the Data Includes
- Time period: 2019 through 2025 (updated monthly)
- Coverage: All domestic flights operated by US carriers that report to the DOT
- Metrics: Scheduled and actual departure/arrival times, delay minutes, cancellations, delay causes, distance
- Volume: Over 42 million individual flight records
How We Process the Data
- Download: Monthly data files are downloaded from the BTS website in CSV format
- Aggregate: Individual flight records are aggregated by airport, airline, route, month, hour, and day of week
- Calculate: On-time percentages, average delays, cancellation rates, and delay cause breakdowns are computed
- Rank: Airports, airlines, and routes are ranked by on-time performance
- Score: Each entity receives a Delay Score (A+ to F) based on its on-time percentage
Delay Score Methodology
| Score | On-Time Rate | Meaning |
|---|---|---|
| A+ | 90%+ | Excellent — rarely delayed |
| A | 85-89% | Very good — occasional delays |
| B | 80-84% | Good — some delays expected |
| C | 75-79% | Average — frequent delays |
| D | 70-74% | Below average — expect delays |
| F | Below 70% | Poor — delays are common |
Definitions
- On-Time: A flight that arrives within 15 minutes of its scheduled arrival time (FAA standard)
- Average Delay: The mean arrival delay in minutes, calculated only for flights that were delayed
- Cancel Rate: Percentage of scheduled flights that were cancelled
- Carrier Delay: Delays within the airline's control (maintenance, crew, aircraft cleaning, baggage loading)
- Weather Delay: Delays caused by significant weather events
- NAS Delay: National Aviation System delays (air traffic control, airport operations, heavy traffic volume)
- Security Delay: Delays caused by security operations (evacuations, re-screening)
- Late Aircraft Delay: Delays caused by the incoming aircraft arriving late from a previous flight
Limitations
- Only includes flights operated by carriers that report to the DOT (covers ~95% of domestic passenger flights)
- Does not include international flights unless operated by a US carrier on a domestic segment
- Historical data quality may vary; some months may have incomplete reporting from certain carriers
- This site shows historical statistics — it is not a real-time flight tracker
Update Schedule
BTS releases data approximately 2-3 months after the reporting month. We update our statistics as soon as new data becomes available.