flight recorder

flight recorder, instrument that records the performance and condition of an aircraft in flight. Governmental regulatory agencies require these devices on commercial aircraft to make possible the analysis of crashes or other unusual occurrences. Flight recorders actually consist of two functional devices, the flight data recorder (FDR) and the cockpit voice recorder (CVR), though sometimes these two devices are packaged together in one combined unit. The FDR records many variables, not only basic aircraft conditions such as airspeed, altitude, heading, vertical acceleration, and pitch but also hundreds of individual instrument readings and internal environmental conditions. The CVR records verbal communication between crew members within the aircraft’s cockpit as well as voice transmissions by radio. Aircraft sounds audible in the cockpit are also caught on the recorder. Flight recorders are commonly carried in the tail of the aircraft, which is usually the structure that is subject to the least impact in the event of a crash. In spite of the popular name black box, flight recorders are painted a highly visible vermilion colour known as “international orange.”

The voice and instrument data processed by the flight recorder are stored in digital format on solid-state memory boards. At least 2 hours of cockpit sound and up to 25 hours of flight data are stored, new data continuously replacing the old. The memory boards are housed within a box or cylinder called the crash-survivable memory unit. This is the only truly survivable component of the flight recorder; the other components, such as the data processor, are not necessary for retrieval of data. Consisting of a heavy stainless steel shell wrapped within layers of insulating material and covered by an aluminum housing, a memory unit is expected to survive impacts of 3,400 g (units of gravitational acceleration), flame temperatures as high as 1,100 °C (2,000 °F), and pressures encountered at 6,000 metres (20,000 feet) underwater. In the event of a crash at sea, flight recorders are equipped with a sonar device that is designed to emit an ultrasonic locator signal for at least 30 days.

In 1939 French engineers François Hussenot and Paul Beaudouin invented a flight recorder, the “type HB” (later called the “hussenograph”), that recorded altitude and speed information on a piece of photographic film. During World War II, analyzing crashes of military aircraft became important. In the United Kingdom, engineers Len Harrison and Vic Husband developed a system that recorded aircraft data on copper foil and could survive a crash. In Finland, engineer Veijo Hietala in 1942 developed a unit nicknamed the “Mata-Hari” that recorded test-flight data on photosensitive paper, which sometimes survived a crash. The U.S. Army Air Forces experimented with recording cockpit voice data on a magnetic wire.

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As civil aviation developed in the years after World War II, “crash-survivable” flight recorders came to be seen as a valuable tool in analyzing aviation disasters and contributing to the design of safer aircraft. However, truly serviceable flight recorders that had any chance of surviving plane crashes were not produced until several years after the war. A series of disastrous crashes of De Havilland Comet jetliners in 1953–54 spurred David Warren, a scientist at Australia’s Aeronautical Research Laboratory (ARL), to design the first combined FDR and CVR. The recording medium for Warren’s ARL Flight Memory Unit was steel wire of the type then being used in magnetic audio recorders. Warren’s invention became the basis for subsequent flight recorders. Although Warren’s recorder, as produced commercially by S. Davall & Son beginning in 1960, was housed in an egg-shaped casing that was painted red, the term black box, which arose during World War II as slang for sensitive aircraft components that were encased in black metal boxes, was applied to the device.

Parallel developments occurred elsewhere in the world. In the United States, James J. Ryan, an engineer employed by General Mills, in 1953 developed the VGA Flight Recorder, which sensed changes in velocity (V), gravitational forces (G), and altitude (A) and inscribed the measurements on a slowly moving strip of aluminum foil. As released in 1953 and sold by General Mills to the Lockheed Aircraft Company, the entire apparatus was enclosed in a yellow-painted spherical shell. Numerous other devices were produced employing various recording media, from metal strips to, eventually, magnetic tape.

During the 1960s, crash-protected FDRs and CVRs became mandatory on airliners around the world. Most flight recorders employed magnetic tape, but during the 1990s a great advancement came with the advent of solid-state memory devices. Memory boards are more survivable than recording tape, and the data stored on them can be retrieved quickly by a computer carrying the proper software. A complete picture can be created of conditions on the aircraft during the recorded period, including a computer-animated diagram of the aircraft’s positions and movements. Verbal exchanges and cockpit sounds retrieved from CVR data are transcribed into documents that are made available to investigators along with the actual recordings. The release of these materials to the public is strictly regulated.