| National aviation system: Delays 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. |
| Late arriving aircraft: A previous flight using the same aircraft arrived late, causing the subsequent flight to depart late. |
| Airline: Delays that were within the control of the airlines, such as aircraft cleaning, baggage loading, crew issues, or maintenance. |
| Extreme weather: Delays caused by serious weather conditions that prevent the operation of a flight, such as tornadoes, snow storms, and hurricanes. |
| Security: Delays caused by the evacuation of an airport, reboarding due to security breach, inoperable screening equipment, and/or long lines at the passenger screening areas. |
