How come i hear multiple helicopters EVERY night?

I worked at the airstation at Camp Pendletom for many years. Since we werre by the coast the fog would cover the runway a lot. When ever we would get a large aircraft like a C-17 or C-5 trying to land in heavy fog they would do low passes and loops a lot so that they were certain they were landing at the beggining of the runway. They didnt want to land halfway through the runway because it took them a while to stop.