How are stadium flyovers coordinated?

Every (American) sporting event I've ever seen include a flyover at the end of the national anthem was coordinated perfectly to where the flyover occurred right at the end of the anthem. This does not seem like an easy feat, and I'd really like to know how it's done.

I've never seen a flyover that wasn't right on time, and it's just exceptionally impressive.

Sorry if this is the wrong place to ask.