The National Transportation Safety Board, during hearings on Thursday, grilled officials from the Army, air traffic controllers and members from the Federal Aviation Administration over protocols following the January deadly air collision between a Black Hawk helicopter and a passenger jet approaching Ronald Reagan Washington National Airport (DCA.

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

The National Transportation Safety Board questioned witnesses Friday on collision avoidance technology and organizational systems to manage risk. It is the third and final day of investigative hearings probing January’s midair collision between a US Army Black Hawk helicopter and an American Airlines regional jet,