NTSB hearings and documents revealed failures by the Army and FAA in the Jan. 29 crash of an American Airlines jet and an Army Black Hawk that killed 67.

Investigators so far have highlighted several factors that may have contributed to the collision, which left 67 people dead.

The National Transportation Safety Board will question witnesses Thursday about air traffic control training, a key part of the investigation into January’s deadly midair collision at Ronald Reagan Washington National Airport.