Empire, on the other hand, has a very tight and exact structure that is dictated by the lyrics. It's very programmatic, the music is there to tell a story. There's an interview with Bruce where he talks about writing it and how he'd write one section and then ask himself "what happens next in the story". That totally comes through in the music. The S.O.S part is awesome because it's musical foreshadowing. The crash hasn't happened yet, but we all know it's coming. This is a nuance that Maiden hasn't really used before. Usually the music is tonally appropriate to the lyrics, but it never goes as far as to actually provide imagery to the lyrics like in Empire. As for the repetition of that part, it creates dramatic tension. Bruce is slapping us in the face with what's yet to come. He's emphasizing an important part through music.