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percent of delayed time

^aIncludes weather events that prevent flying. Other weather delays that slow operations are included under other categories. ^bDelay resulting from a previous flight with the same aircraft arriving late.

Key: NAS = Delays attributable to the national aviation system (NAS) that refer to a broad set of conditions, such as non-extreme weather, airport operations, heavy traffic volume, and air traffic control.

Note: Percents do not add to 100 due to rounding.

Source: U.S. Department of Transportation, Bureau of Transportation Statistics, Office of Airline Information, available at www.bts.gov as of September 2014.