Investigators are still in the early stages of determining why the American Airlines passenger jet and Army helicopter collided as the plane prepared to land Jan. 29. Both plunged into the Potomac River, killing everyone aboard. It will likely take more than a year to complete the final report.

A congressional hearing Thursday reinforced the idea that the January midair collision between an American Airlines passenger jet and an Army helicopter that killed all 67 people aboard both aircraft could have been prevented.

The head of the National Transportation Safety Board that is investigating the crash is appearing along with the leaders of the Federal Aviation Administration and the Army’s aviation