U.S. authorities restricted helicopter flights near Reagan Washington National Airport on Friday, after a midair collision between an American Airlines passenger jet and a military helicopter killed 67 people this week.

Investigators confirmed they have recovered a cockpit voice recorder and a flight-data recorder from American Eagle Flight 5342, which will undergo analysis.

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.