Flight Data Recorders Not Recovered Yet

An American Airlines regional jet went down in the Potomac River near Ronald Reagan Washington National Airport.
What is a black box, what can it tell us, and have the data recorders been found from Flight 5342 and the Army's Blackhawk?
The black boxes are the nickname for the flight data recorder and cockpit voice recorder that record events during a flight.
An American Airlines jet carrying 64 people collided Wednesday with a helicopter near Reagan Washington National Airport, ...
The NTSB says it has recovered data collectors from a jet carrying 64 people after it collided with an Army Black Hawk ...