The first of the National Transportation Safety Board’s three days of investigative hearings is underway to help determine what caused the deadly midair collision on January 29 between an Army helicopter on a training mission and American Airlines flight 5342 landing at Ronald Reagan Washington National Airport.

The NTSB is holding three days of hearings to uncover insights into what caused the fatal crash between the passenger jet and the army helicopter over Ronald Reagan National Airport in January.

A National Transportation Safety Board hearing revealed that the U.S. Army was aware of altitude discrepancies on Black Hawk helicopters.