Inside the Sphere by M. L. Buchman

New York City is still there, but no one can enter.

No one except the best pilot on the planet, his copilot, and a flight of hopefuls. Those who enter the city become geniuses or idiots... or worse.

For ten years, Trevor Hollman has beaten the odds and flown the hopefuls into the city and the survivors back out. But his world is about to change