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,

Washington, DC (CNN) — In more than 32 hours of testimony across three days the National Transportation Safety Board probed virtually every detail of what led up to the January 29 midair collision between a US Army Black Hawk helicopter and an American Airlines regional jet, operated by PSA airlines.

A three-day National Transportation Safety Board hearing on the deadliest U.S. aviation accident in decades dug into problems with altimeters, chopper routes and the busy Washington, D.C., airspace.