For the most part, the planes in The Giver are delivering supplies to the Community. We never learn exactly what supplies they provide, but while the Community seems fairly self-sufficient, it is clear that they need some things from the world outside.
When planes do land with supplies, they land on the other side of the river from the Community, so that no one in the Community can have any contact with them. Children watch them from their side of the river because they are curious about anyone or anything from Beyond.
However, the pilots always take off away from the Community, not permitted to fly over it. On one occasion in the past, a pilot had done so, and the response of the Community was as though this was a national disaster. All the people were ordered to go inside and stay there until there was an "All clear" signal. It turned out that this was a pilot who was in training who had made an error in navigation. The pilot was Released as a consequence, a rather severe penalty for a navigational error.
We learn all of this in the first two pages of the book, and it tells us something about the nature of the Community. This is a community that is deliberately isolating itself from the outside world, with a response that seems all out of proportion to a mere accident. This draws us into the story, to wonder why a community would act in this way, and as the story unfolds, we begin to understand why.