But even before the National Transportation Safety Board completes its investigation—a neurotically thorough process that will probably take about a year, and thus meshes poorly with the news cycle and the conspiracy-theorist cycle—it is easy to see some of the lines of inquiry that crash detectives will pursue.

In the three years before the deadly collision between an Army helicopter and an American Airlines flight near Reagan National Airport, at least two other pilots reported near-misses with helicopters while landing at the airport,

The Wall Street Journal examined flight route and elevation data to show the moments before American Airlines Flight 5342 fatally collided with ​an Army Black Hawk helicopter.

Upon first approach, Republic Airways Flight 4514 diverts from course, circles around, and lands during a second attempt at Reagan National Airport.