Which of the following is NOT a factor in flight delays?

Passenger preference changes are indeed not a typical factor in flight delays. Typically, flight schedules and operations are dictated by the airline's logistical planning and regulations, rather than personal preferences of passengers. While individual preferences can influence decisions, such as seat assignments or boarding procedures, they do not normally lead to systemic delays within the larger framework of air traffic management.

In contrast, weather conditions are a well-known factor that can severely impact flight operations, requiring adjustments to avoid hazardous conditions. Air traffic control restrictions arise from the need to manage the flow of air traffic safely and efficiently, which can lead to delays if congestion occurs or when certain routes are temporarily closed. Ground service delays are also significant, as the timely provision of services such as fueling, maintenance, and boarding can directly affect departure times. Each of these factors plays a critical role in the scheduling and operational efficiency of airlines, making them common causes of flight delays.