Which situation can lead to a deviation in flight schedules due to external conditions?

The situation that can lead to a deviation in flight schedules due to external conditions is related to force majeure. Force majeure encompasses unforeseen events or circumstances that are beyond the control of the airlines or aviation authorities, such as natural disasters, extreme weather conditions, geopolitical events, or widespread health emergencies. These situations can disrupt standard operating procedures, making it necessary for airlines to alter or cancel flight schedules, reroute aircraft, or delay departures.

While a diverted flight can impact scheduling, it is often a response to specific operational needs rather than a broad external condition. "Group" typically refers to arrangements for a set number of passengers and does not inherently influence flight operations as a deviation. "First Rider" does not pertain to external conditions affecting flight schedules and instead refers to a ticketing or passenger policy that does not influence operational logistics. Hence, force majeure is the most encompassing option that highlights the effects of uncontrollable external conditions on flight schedule deviations.