防空識別圏
A private pilot since 1988, O’Brien also reported extensively on civil aviation issues and crash investigations. O'Brien reported the airliner crashes of US Airways Flight 427, ValuJet 592, TWA 800, EgyptAir 990, American Airlines 587, Comair 5191, John F. Kennedy Jr., Payne Stewart, Paul Wellstone, the C-150 incursion into the Washington DC Air Defense Identification Zone, and the Cory Lidle crash in Manhattan. In the wake of the September 11 attacks, O'Brien provided viewers radar tracks of the hijacked flights while the twin towers were still standing. During the Afghanistan and Iraq invasions, he, along with various retired generals, reported on military aviation techniques and strategy.