An American Airlines jet and an Army helicopter collided over Washington, D.C., Wednesday night. All 67 people aboard the aircraft are presumed dead.

The so-called “black box” is one of the most important pieces of forensic evidence following a plane crash. There are actually two of these remarkably sturdy devices.

An American Airlines plane with 64 people on board collided with an Army helicopter over Washington, D.C., and crashed into the Potomac River.