The cockpit voice recorder from the downed Alaska Airlines Flight 261, held by the robotic arm of the remotely piloted vehicle that retrieved it.

Photo courtesy U.S. Department of Defense

After the crash, they didn't find a single body for five days. Even with military and civilian personnel frantically scouring the seas, it was as if Air France Flight 447 had simply vanished over a remote area of ocean 600 miles from Brazil -- with 228 people onboard. It didn't happen in the early days of the airline industry; it occurred in 2009, on a fancy modern aircraft controlled by a competent company.

Airplane accidents are statistical rarities. But when they happen, they're often fatal, and people want answers as to why their loved ones died.

There are usually many unanswered questions as to what brought the plane down. Investigators turn to the airplane's flight data recorder (FDR) and cockpit voice recorder (CVR), also known as "black boxes," for answers. Following any airplane accident in the U.S., safety investigators from the National Transportation Safety Board (NTSB) immediately begin searching for the aircraft's black boxes.

It took investigators nearly two years to find the FDR from Flight 447. The box had not only survived impact, but also being submerged under nearly 13,000 feet of salty, corrosive seawater. In the end, the data proved that pilot error had contributed to a stall that eventually caused the crash.

These recording devices, which cost between $10,000 and $15,000 each, reveal details of the events immediately preceding the accident. In this article, we will look at the two types of black boxes, how they survive crashes, and how they are retrieved and analyzed.