How could DC crash happen?

CONGESTED, COMPLEX AIRSPACE | Some aviation experts point to near misses in the past, say disaster was waiting to happen; black boxes found

- Agencies

The black boxes for a commercial flight that collided with a military helicopter in Washington DC have been located even as questions mount about staffing and other close calls at the airport that one expert described as "the most controlled bit of air-space in the world", where the plane was landing. There was no immediate word on the cause of the collision, but officials said flight conditions were clear as the jet arrived from Wichita, Kansas.

Officials are still investigating the cause of the accident that killed all 67 people aboard the two aircraft. The National Transportation Safety Board (NTSB) said a preliminary report will be issued in 30 days. The flight data recorder and the cockpit voice recorder, known as the black boxes, can help offer clues to investigators about what may have gone wrong on the flight.