This study investigates the impact of four subcategories of flight delays on total flight delays over the period from May 2005 through December 2019. Total flight delays are divided into weather, air carrier, security, and non-weather National Aviation System (NAS) delays. Using the flight data provided by the Air Travel Consumer Report of the U.S. Department of Transportation for a consistent set of ten airlines, each time- series is decomposed. Trend and seasonality are determined. Total flight delays, and each of its subcategories, demonstrate strong seasonality and follow a random walk model without drift during the sample period. Total flight delays are composed of approximately one-half air carrier caused, one-third weather related, and one-sixth non-weather NAS delays. In the period prior to 2012, weather, air carrier, non-weather NAS, and security delays follow the same pattern as total flight delays. After 2012, air carrier and non-weather NAS (infrastructure) delays follow a similar pattern as total flight delays, but weather and security delays are far fewer than would be suggested by the pattern of total delays. The latter period was consistent with a period of increased investment in “disruption management,” which may have had the desired effect on weather and security delays. Flight delays under the control of air carriers or from infrastructure issues (non-weather NAS delays) increased from 2012 through 2019.