Plane crashes often leave a lot of unanswered questions. This makes investigators turn to the airplane's black boxes for answers. Since its widespread use after the post-World War II era, these recording devices that store flight data and pilots’ conversations have evolved to help investigators shed some light on the accidents in the air and on the land. 

Why a black box?

There are several versions of why flight recorders are called black boxes. The name could relate to the World War II era's first electronic modules that were installed on military aircraft. Because of photographic film used for recording, such boxes should not let light in, as it could damage the tape. So they were painted black to prevent reflection. According to the other version, the name may come from early engineering design philosophies, where boxes that contained electronic components were termed as black boxes. 

The first flight recorder (FDR) was introduced by Professor James J. Ryan, a graduate of the University of Iowa and University of Pittsburgh engineering schools. 

During WWII, the U.S. Army Air Corps and Civil Aeronautics Board started working on the development of survivable flight data recorders. The company’s mechanical division hired James J. Ryan. 

His 16-pound hatbox-sized recorder was divided into two compartments, with the recording equipment (tiny electric motor with a thin sheet of 2-inch-wide aluminum foil) positioned above and measuring devices (the altimeter, the accelerometer, and the airspeed indicator) below. It could operate for 300 hours without servicing and could be easily mounted in any aircraft’s tail section. Ryan's recorder was released in 1953 and later sold to Lockheed Aircraft Company, which kept the device's basic features. By 1957, all planes over 12,500 pounds were required to have FDRs. 

David Warren, a research scientist from the Aeronautical Research Laboratory* (ARL) of Melbourne, introduced his cockpit voice recorder (CVR) in 1958. Warren was a member of the research group, which was involved in the accident investigation related to the mysterious crash of the world’s first jet-powered commercial aircraft, the Comet. Warren’s CVR consisted of wire, used as the recording mechanism, which was placed in a titanium box. After the plane crash at Mackay, Queensland in 1960, it was recommended to install cockpit voice recorders on all airliners. Australia was the first country in the world to make cockpit-voice recording compulsory.

How Black Boxes are made? 

Flight recorders cost between $10,000 and $15,000 each. They are made to withstand loads and remain intact in a wide variety of emergency scenarios. 

Before being approved for use, they are tested. Recorders must withstand impact on a concrete wall at a speed of 750 km/h, a pressure of 2.25 tons for at least five minutes, a temperature of up to 1100 degrees Celsius for at least an hour, and be found at a depth of up to 6000 meters underwater.

Data in modern CVR and FDR recorders is stored on stacked memory boards inside the crash-survivable memory unit (CSMU), a large cylinder that bolts onto the flat portion of the recorder. The memory boards can accommodate two hours of audio data for CVRs and 25 hours of flight data for FDRs. The boxes that store recorders are painted bright orange or red to be easily detectable. 

Types of the black boxes

In addition to conversations between crews and dispatchers, CVR also saves ambient sounds. The records from CVR have an exact timestamp reference. Each of the parameters is recorded several times per second. The recording is carried out in cycles: new data overwrites the oldest. The cycle duration is 17-25 hours to ensure that there is enough storage for any flight.