How an Army Black Hawk helicopter collided into an American Airlines jetliner in a deadly crash over the Potomac River Wednesday night is still unknown, but questions are emerging, including the altitude of the military helicopter.

The NTSB is investigating "thousands of data points" to find the cause of the fatal D.C. plane-helicopter crash, including whether air traffic control staff was short personnel.

The National Transportation Safety Board is an independent federal agency tasked with examining serious transport-related accidents.

Investigators have already recovered the cockpit voice recorder and flight data recorder of the American Airlines plane that collided with an Army helicopter near Ronald Reagan National Airport.

As investigators look into the cause of Wednesday night's plane crash, pilots share their initial take on the collision.

Investigators plan to push forward on Friday with efforts to retrieve the two aircraft involved in a crash in Washington that killed 67 people and raised questions about air safety in the U.S. capital.

After a military helicopter collided with a passenger plane near Reagan National Airport, here’s what to know about TCAS, a system designed to prevent mid-air collisions.