Right. When planes at one airport are delayed, it has a trickle-down effect on other airports. Some planes can be held in the air circling for several minutes before being cleared for landing because there isn’t enough runway space for them to land safely. Other planes can sit on the runway for several minutes waiting to be cleared for takeoff. At other airports, planes can be delayed from taking off if they’re scheduled to land at an airport that is experiencing significant air traffic delays. Even if your son’s plane is there and ready to be boarded, sometimes they’ll delay boarding rather than have people sit on the plane for an hour. These are all deemed “air traffic control delays.”