According to analysis by usa today, air flight is so safe that a person would have to fly everyday for more than 64,000 years before dying in an accident. how can such a statement be justified?

Hey!
Obviously, it's not possible for a single person to fly for 64,000 years. That'd be insane, impossible, and frankly a complete waste of 640 centuries.
However, it's possible that the total flights around the world could be combined to make a single time, and cutting off every time there does happen to be a casualty.
A method that wouldn't be very accurate but considerable is making a ratio of time in which there's been no casualties and scaling it up to a larger scale like the one we've been provided.
Hopefully this helps!