Extreme weather: Cancellations caused by serious weather conditions that prevent the operation of a flight, such as tornadoes, snow storms, and hurricanes. |
National aviation system: Cancellations attributable to a broad set of circumstances affecting airport operations, heavy traffic volumes, and air traffic control. This includes any nonextreme weather condition that slows the operation of the system, such as wind or fog, but does not prevent flying. |
Airline: Cancellations that were within the control of the airlines, such as aircraft cleaning, baggage loading, crew issues, or maintenance. |
Security: Cancellations caused by the evacuation of an airport, reboarding due to security breach, inoperable screening equipment, and/or long lines at the passenger screening areas. |