BTS Home > Frequently Asked Questions

Airline On-Time Performance and Causes of Flight Delays

• How do we explain the causes of flight delays and cancellations?
• Which airlines report on on-time performance and, since June 2003, on the causes of flight delays?
• What types of flight delays are reported to BTS by the airlines?
• How were the reporting categories determined?
• What flights does the reporting cover?
• What airports does the reporting cover?
• How are flight delays calculated?
• For how long have airlines reported on-time performance?
• What types of data are published?

Which airlines report on on-time performance and, since June 2003, on the causes of flight delays?
On-time numbers are reported each month to the Department of Transportation's Bureau of Transportation Statistics (BTS) by the 20 U.S. air carriers that have at least 1 percent of total domestic scheduled-service passenger revenues. The reports cover nonstop scheduled-service flights between points within the United States (including territories) as described in 14 CFR Part 234 of DOT's regulations.

The airlines required to report are:

Also, Aloha Airlines (AQ) and Pinnacle Airlines (9E) will report voluntarily.

What types of flight delays are reported to BTS by the airlines?
Airlines that report monthly numbers of flight delays to the BTS began reporting information on causes of delays in June 2003. The airlines report the causes of delays in five broad categories:

• 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.).
• 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.
• 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.
• Late-arriving aircraft: A previous flight with same aircraft arrived late, causing the present flight to depart late.
• 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.

How were the reporting categories determined?
The U.S. Department of Transportation issued a final rule on reporting the causes of flight delays on November 25, 2002. The final rule followed two years of consideration.

DOT formed an Air Carrier On-Time Reporting Advisory Committee in August 2000 to consider changes to the current on-time reporting system so that the public would have clear information about the nature and sources of airline delays and cancellations. This task force recommended the creation of a reporting framework for collecting information about the causes of airline delays and cancellations.

In 2001, BTS conducted a pilot program with four airlines to test the monthly reporting of causation. BTS based the final rule on the recommendations of the task force, the results of its pilot project, its outreach efforts to the aviation community and comments received after a proposed rule was published in December 2001.

To view a copy of the rule, go to the Docket Management System website, http://dms.dot.gov/, and follow the instructions for viewing the documents in Docket No. OST 2000-8164.

What flights does the reporting cover?
The rule requires carriers to report on operations to and from the 32 U.S. airports that account for at least 1 percent of the nation's total domestic scheduled-service passenger enplanements. However, all reporting airlines have voluntarily provided data for their entire domestic systems.

What airports does the reporting cover?
The 32 reportable airports are:

How are flight delays calculated?
A flight is counted as "on time" if it operated less than 15 minutes later the scheduled time shown in the carriers' Computerized Reservations Systems (CRS). Arrival performance is based on arrival at the gate. Departure performance is based on departure from the gate.

For how long have airlines reported on-time performance?
Airlines have reported on-time performance to the U.S. Department of Transportation since 1987. Reporting was modified in 1995 to include reporting of mechanical delays, which had not been included in the original rule. Monthly reports are released in the Air Travel Consumer Report.

What types of data are published?
The U.S. Department of Transportation publishes a monthly summary of airline on-time performance, including causes of delay, in the Air Travel Consumer Report (http://airconsumer.ost.dot.gov/reports/index.htm )

The Bureau of Transportation Statistics publishes a variety of on-time and flight delay information.