The National Transportation Safety Board has opened public hearings on a January midair collision between an Army Black Hawk helicopter and a commercial jet.

Investigators probing the January midair collision of a passenger plane and an Army helicopter over Washington that killed 67 people found the chopper was flying higher than it should have been and its altitude readings were inaccurate.

The board opened the three days of hearings by showing an animation and playing audio and video from the night of the collision, as well as questioning witnesses and investigators about how the Federal Aviation Administration and the Army may have contributed to nation’s deadliest plane crash since November 2001.