A long list of things went wrong in January and contributed to the collision between an Army helicopter and an American Airlines jet over Washington, D.C., that killed 67 people.

The deadly mid-air collision at Reagan Airport in January was years in the making, the operations manager of the DCA air traffic control tower on the night of the accident told the National Transportation Safety Board on Friday.

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