The number of flights not departing or arriving on time, cancellations, and diversions are measures of service quality. These indicators are strongly seasonal and are affected by weather and heavy demand in winter and summer months, respectively.
|Number of scheduled flights||438,099||527,083|
|Percent change from same month previous year||-13.90||20.31|
|Percent of flights not arriving on time||17.42||13.12|
|Change from same month previous year||-3.38||-4.30|
|Percent of flights not departing on time||13.93||10.80|
|Change from same month previous year||-3.83||-3.14|
|Percent of cancelled flights*||1.03||1.16|
|Change from same month previous year||-1.20||0.13|
|Percent of diverted flights**||0.16||0.13|
|Change from same month previous year||-0.02||-0.04|
NOTE: The counted value is compared to the value from the same period in the previous year to account for seasonality. Data for American Eagle was included starting in January 2000. Percent changes from January 1999 to January 2000 were calculated based on data excluding American Eagle. Aloha Airlines, which reported on-time statistics for October 2000 through November 2001, has been excluded to retain comparability.
The data cover the 10 largest U.S. air 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 one that was not operated but was listed in a carrier's computer reservation system within seven calendar days of the scheduled departure. A diverted flight is one that left from the scheduled departure airport but flew to a destination point other that the scheduled destination point.
A trendline has been provided for flights not arriving on-time. The trend has been calculated through a statistical procedure called Structural Modeling, in which the time series under study is decomposed into seasonal, trend and irregular components. For further information on this statistical procedure, see: S.J. Kiipman, et al., Structural Time Series Analyser, Modeller and Predictor (STAMP), London: Timberlake Consultants Ltd., 2000.
The dramatic changes in the September 2001 data reflect the impact of the terrorist attacks on September 11, 2001, on aviation, including several days in which commercial air operations were suspended.
Certain flights origination at O'Hare airport and operated by American Airlines (181flights in April) and United Airlines (256 flights in April) between April 24, 2002 and May 8, 2002 are not included in the calculations due to the participation of these carriers in a pilot test program for enhanced baggage screening. A list of affected flights is available from BTS.
SOURCE: U.S. Department of Transportation, Bureau of Transportation Statistics, Airline Service Quality Performance data.