Monthly data, not seasonally adjusted
The share of flights arriving on time is a measure of service quality. Not only is this indicator strongly seasonal, but the data also reflect the effects of weather. For the ten-year period ending 2009, 20.1% of flights were delayed, 1.8% were cancelled, and 0.2% were diverted. These data only cover major airlines, which are required to report delays.
|Flight On-Time Performance||Dec-09||Dec-10|
|Number of scheduled flights||291,026||295,401|
|Percent change from same month previous year||-6.1||1.5|
|Percentage of flights arriving on-time||74.47||73.53|
|Difference from same month previous year*||7.3||-0.9|
* Current month minus same month previous year. This is generally used in the case of bound numbers, such as proportions that cannot exceed 100%.
NOTES: The current value is compared to the value from the same period in the previous year to account for seasonality. Data are available for those carriers that had at least 1% of domestic enplanements in the previous year. The last 25 months of data include only carriers that reported in each of the last 25 months to retain comparability. Earlier data includes all reporting carriers.
A scheduled operation consists of any nonstop segment of a flight. The term "late" is defined as 15 minutes after the scheduled departure or arrival time. A "cancelled" flight is a flight that was not operated but was in the carrier's computer reservation system within 7 days of the scheduled departure. A "diverted" flight is a flight which is operated from the scheduled origin point to a point other than the scheduled destination point in the carrier's published schedule.
SOURCE: U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, Office of Airline Information, Flight Delays at-a-Glance, available at http://www.bts.gov/programs/airline_information/ as of February 2011.