Weather: The most common cause of a flight delay is bad weather. The plane is late: If the planet's late, there's obviously delays. Crew members showing up late: Sometimes crew members don't show up on time. Usually it's flight attendants, but it could also be the pilot.

Flight delays are rarely caused by a single factor but are usually the result of a "knock-on" or "domino" effect within a highly complex global network. The most common culprit is "late arrival of incoming aircraft," where a delay in one city cascades through the rest of the plane's schedule for the day. Weather is another primary factor; even if it is sunny at your departure gate, storms at your destination or along the flight path can trigger Air Traffic Control (ATC) restrictions. Furthermore, technical maintenance issues, which must be addressed for safety regardless of the schedule, can cause sudden pauses. Ground operations also play a role, including late refueling, slow baggage loading, or waiting for connecting passengers and their luggage. Finally, congested airspace and limited runway capacity at major hubs often mean planes must wait for a "slot" to depart. Because airlines operate on razor-thin margins of time to maximize efficiency, even a ten-minute hiccup in cleaning the cabin can result in a recorded departure delay.