Do more U.S. airports need control towers? That's one of the questions that has arisen following a midair collision at an airport in southern Arizona last week.

Without an air traffic control tower, it's a calculated dance that requires communication by pilots. Two small planes collided in midair over one of the runways on the outskirts of Tucson last week.

Without an air traffic control tower, it’s a calculated dance that requires communication by pilots. Two small planes collided in midair over one of the runways on the outskirts of Tucson last week.

Without an air traffic control tower, it’s a calculated dance that requires communication by pilots. Two small planes collided in midair over one of the runways on the outskirts of Tucson last week.

Without an air traffic control tower, it's a calculated dance that requires communication by pilots. Two small planes collided in midair over one of the runways on the outskirts of Tucson last week.