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.

It's one of the most important pieces of forensic evidence following a plane crash: The so-called “black box." There are actually two of these remarkably sturdy devices: the cockpit voice recorder and the flight data recorder.

While authorities focus on the cause of the US's deadliest aviation disaster since 2001, families are mourning their loved ones. Here's the latest.