At their closest points, helicopters and planes routinely flew within 75 feet near the airport, according to the NTSB.

The National Transportation Safety Board (NTSB) on Thursday morning will resume its probe into the deadly collision of an Army helicopter and passenger plane near Reagan Washington National

Incorrect altitude readings on the Army helicopter that collided with a passenger plane over Washington, D.C., in January contributed to the aircraft getting too close, but air traffic controllers warned about the hazards helicopter traffic presented years before the crash.