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,

The board focused on air traffic control and heard it was common for pilots to ask to use visual separation — relying on eyesight — just as the Army Black Hawk’s pilot agreed to do the night of the crash.

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.

The Army helicopter that collided with a plane over D.C. in January had incorrect altitude readings, contributing to the aircraft getting too close.