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The most important condition of life in the community where The Giver is set is Sameness, meaning that unusual or unexpected events are to be eliminated and avoided by any means necessary.
The sighting of a jet plane flying over the community is highly unusual because "it was against the rules for Pilots to fly over the community." The reasoning for the prohibition against flight over the community is inferred to be for the community's safety.
When the supplies were delivered by cargo planes to the landing field across the river, the children rode their bicycles to the riverbank and watched, intrigued, the unloading and then the takeoff directed to the west, always away from the community.
This is why everyone in the community was instructed to go indoors shortly after the jet was sighted in the air.
For the pilot of the jet that violated this basic rule of the community, there was no acceptable means of apologizing and correcting the mistake. Punishment was necessary for the enormous disturbance and disruption caused by the flight, for the apprehension it caused the residents of the community and for the way in which it destroyed the Sameness of every day's events. The only way of dealing with the pilot was for him to be released - removed from the community so that he would not pose any threat of unacceptable behavior.