Flight delays can occur for a number of reasons ranging from weather conditions to air traffic control. Airports need to manage a large number of planes arriving and departing at different times throughout the day. This can cause flight delays when airplane traffic becomes congested, or if flights have to be redirected due to weather or other factors. Airlines are also subject to maintenance, crew availability and other unforeseen issues that can delay flights. Additionally, security measures and heavy passenger loads can also cause flight delays.