July 31 (Reuters) - The National Transportation Safety

Board is probing air traffic control staffing, flight volume,

training and other procedures in the investigation into the

collision between an Army helicopter and an American Airlines ( AAL )

regional jet that killed 67 people.

The board is holding a hearing Thursday looking at issues at

Ronald Reagan Washington National Airport before the Jan. 29

collision over the nearby Potomac River that was the deadliest

U.S. air disaster in more than 20 years.