When an aviation accident occurs, an aircraft’s black box often provides the only available clues as to what went wrong. The information that these devices record allows transportation safety investigators to recreate the circumstances surrounding the incident, helping them analyze the aircraft’s performance, pinpoint the pilot’s reactions, and even create a digital reproduction of the accident.
To assist authorities in locating them, black boxes are actually bright orange, although earlier iterations of the device include Boeing’s yellow sphere and the UK’s “Red Egg” flight recorder. Modern black boxes are most often comprised of two separate recording devices—one for audio and one for data—and are usually located in the tail of the plane. The cockpit voice recorder (CVR) digitally records sounds from microphones, earphones, and area recorders in the cockpit and is battery-powered to guard against potential electrical failures. Using CVR data, crash investigators can analyze the sounds of the aircraft’s engine, emergency pings, and stall warnings to determine its speed and engine RPM and potentially deduce the cause of the accident. Recordings of the crew’s communications with ground-based flight controllers and each other can provide further insight into the circumstances surrounding the crash and can also assist with creating an accurate incident timeline.
In addition to the CVR, the flight data recorder (FDR) uses a device known as a flight data acquisition unit to collect information on approximately 90 flight performance parameters, including speed, direction, altitude, and such sensitive details as individual wing flap movements. The flight data acquisition unit stores new information every few seconds, collecting data more frequently if problems are detected during the flight.
As a tool designed to aid plane crash investigations, a flight recorder must be capable of withstanding extremely harsh conditions. International civil aviation regulations mandate that CVRs and FDRs be able to withstand sustained high-temperature fires, 3,400-G crash impacts, and extreme pressure at depths of 20,000 feet under water. Black boxes continue to emit locator signals for up to 30 days following a crash, and each device is equipped with an Underwater Locator Beacon (ULB), which activates immediately upon contact with water and can transmit from up to 14,000 feet beneath the surface.
Although they are designed to withstand emergency situations, aircraft black boxes provide information that can be used during routine aircraft maintenance. Crews and their airlines can periodically check data from previous flights to monitor the airplane’s performance, and flight data can also offer insight into metrics such as fuel efficiency.
Both international and domestic civil aviation organizations have issued requirements regarding cockpit voice and flight data recorders. The United Nation’s civil aviation agency, the International Civil Aviation Organization (ICAO), requires that all fixed wing aircraft and helicopters carry a CVR with a recording duration of at least 30 minutes, while fixed wing airplanes with a maximum takeoff mass exceeding 5,700 kg and an airworthiness certificate issued after January 1, 2003, must have CVRs capable of recording at least two hours. ICAO has similar requirements for FDRs, while also defining separate classes and types of the device. For example, provision 6.3.6 of Annex 6, Volume 1 states that aircraft with a maximum takeoff mass of more than 5,700 kg that have obtained airworthiness certification after January 1, 2005, must carry a Type 1A FDR, which can record flight path, speed, altitude, engine power, and certain other data. In the United States, the Federal Aviation Administration (FAA) enforces additional regulations concerning black boxes, including rules that mandate the types of FDRs and CVRs that various types of aircraft must have.
The Birth of the Black Box
The world’s first jet-powered commercial airliner, the de Havilland Comet, completed its first prototype flight on July 27, 1949. Tragically, many of the early Comets crashed during the early 1950s, and authorities were never able to uncover the cause of many of these high-profile accidents. Due to the lack of flight records, this inability to explain crashes was standard during the early days of civil aviation. Even when eyewitnesses could provide accounts, their anecdotes were rarely enough to help authorities determine the root cause of an accident.
While investigating an accident involving one of the Comets, David Warren, a researcher at Melbourne, Australia’s Aeronautical Research Laboratories, had an idea that would forever change aviation. Driven by the belief that recordings of the pilots’ voices and instrument readings could help determine the cause of plane crashes and prevent future tragedies, he invented the Flight Memory Unit. Released in 1957, the first design of the device recorded on steel wire to document up to four hours of voice and flight instrument data. Future black box models would record on magnetic tape recorders, and today, flight recorders store information on solid-state memory units comprised of stacked memory boards.
The Australian aviation sector initially rejected David Warren’s invention due to privacy concerns, but the Flight Memory Unit eventually gained acceptance among flight safety authorities in Great Britain. It wasn’t long before Warren began producing the first black boxes in crash- and fire-proof enclosures to sell to airlines. After the 1960 crash of a Trans-Australia Airlines flight in Queensland, Australia, investigators were unable to determine the cause of the accident, which still remains the country’s deadliest civil aviation accident. The tragedy spurred the Australian government to mandate that all commercial aircraft carry a flight data recorder, making the country the first to introduce such requirements.