After an airliner crashes investigators begin searching for the so-called black boxes from the plane. Able to survive devastating crashes, these recording devices may provide the best source of information about what exactly happened on board. Here's how they work.
Until recently, most black boxes worked like tape recorders, using magnetic tape to record voice and electronic data. Current manufacturers use solid state memory boards, like the kind used in personal computers. Without moving parts, these black boxes are more reliable than their magnetic tape predecessors.
All airplanes harbor two black boxes: a flight data recorder and a cockpit voice recorder. Typically located in the tail end of the craft, these machines receive data from microphones and sensors throughout the plane, recording information such as airspeed, fuel flow, and cockpit dialogue.
The most important part of a black box is the crash-survivable memory unit. This device consists of a stack of memory cards that store the collected data in digital form. Surrounding the memory cards are a thin layer of aluminum, high-temperature insulation, and finally a stainless steel or titanium shell encasing the other materials. Together, these layers protect the memory cards from the intense heat and destruction of a crash. Black boxes also include a locator beacon that activates on contact with water, allowing searchers to find the device even when a plane goes down at sea.
Although we call aviation recorders black boxes, they're actually bright orange, allowing searchers to locate them more easily amongst wreckage. Although not all recording devices survive intact, most are able to provide enough data to help investigators piece together what happened in the air.