The black boxes of the American Airlines plane submerged in the Potomac River from Wednesday’s crash with a military helicopter have been recovered, the National Transportation Safety Board said late Thursday.

Investigators have recovered the flight recorders—also known as black boxes—from both the commercial jet and the military helicopter involved in the mid-air collision near Reagan National Airport in Washington,

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. One is the