Final answer:
Fog is a major operational concern to pilots because it reduces visibility and can lead to accidents. Pilots have difficulty seeing landmarks, runways, and other aircraft in foggy conditions, which increases the risk of collisions.
Step-by-step explanation:
Fog is a major operational concern to pilots because it reduces visibility and can lead to accidents. When there is fog, pilots have difficulty seeing landmarks, runways, and other aircraft, which increases the risk of collisions. Aircraft also need a certain level of visibility to safely takeoff and land.