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Abstract
This paper analyzes recent trends related to delays, airborne holding and diversions in the National
Airspace System (NAS) during the summer convective weather season. A weather variable is
introduced to help analyze these performance metrics in a way that factors out differences in the
location and intensity of thunderstorms. Regression analysis indicates a nearly 50% increase in
flights delayed more than an hour from summer 2003 to 2005. The increase in delay is associated
with a growing concentration of flights at busy hub airports over the past five years.